Country：Japan

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Some animals have the remarkable capacity for mirror self-recognition (MSR), yet any implications for self-awareness remain uncertain and controversial. This is largely because explicit tests of the two potential mechanisms underlying MSR are still lacking: mental image of the self and kinesthetic visual matching. Here, we test the hypothesis that MSR ability in cleaner fish, Labroides dimidiatus, is associated with a mental image of the self, in particular the self-face, like in humans. Mirror-naive fish initially attacked photograph models of both themselves and unfamiliar strangers. In contrast, after all fish had passed the mirror mark test, fish did not attack their own (motionless) images, but still frequently attacked those of unfamiliar individuals. When fish were exposed to composite photographs, the self-face/unfamiliar body were not attacked, but photographs of unfamiliar face/self-body were attacked, demonstrating that cleaner fish with MSR capacity recognize their own facial characteristics in photographs. Additionally, when presented with self-photographs with a mark placed on the throat, unmarked mirror-experienced cleaner fish demonstrated throat-scraping behaviors. When combined, our results provide clear evidence that cleaner fish recognize themselves in photographs and that the likely mechanism for MSR is associated with a mental image of the self-face, not a kinesthetic visual-matching model. Humans are also capable of having a mental image of the self-face, which is considered an example of private self-awareness. We demonstrate that combining mirror test experiments with photographs has enormous potential to further our understanding of the evolution of cognitive processes and private self-awareness across nonhuman animals.

DOI： 10.1073/pnas.2208420120

Authorship：Last author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Fertilization mode may affect sperm characteristics, such as morphology, velocity, and motility. However, there is little information on how fertilization mode affects sperm evolution because several factors (e.g., sperm competition) are intricately intertwined when phylogenetically distant species are compared. Here, we investigated sperm characteristics by comparing seven externally and four internally fertilizing marine fishes from three different groups containing close relatives, considering sperm competition levels. The sperm head was significantly slenderer in internal fertilizers than in external fertilizers, suggesting that a slender head is advantageous for swimming in viscous ovarian fluid or in narrow spaces of the ovary. In addition, sperm motility differed between external and internal fertilizers; sperm of external fertilizers were only motile in seawater, whereas sperm of internal fertilizers were only motile in an isotonic solution. These results suggest that sperm motility was adapted according to fertilization mode. By contrast, total sperm length and sperm velocity were not associated with fertilization mode, perhaps because of the different levels of sperm competition. Relative testis mass (an index of sperm competition level) was positively correlated with sperm velocity and negatively correlated with the ratio of sperm head length to total sperm length. These findings suggest that species with higher levels of sperm competition have faster sperm with longer flagella relative to the head length. These results contradict the previous assumption that the evolution of internal fertilization increases the total sperm length. In addition, copulatory behavior with internal insemination may involve a large genital morphology, but this is not essential in fish, suggesting the existence of various sperm transfer methods. Although the power of our analyses is not strong because of the limited number of species, we propose a new scenario of sperm evolution in which internal fertilization would increase sperm head length, but not total sperm length, and change sperm motility.

DOI： 10.1002/ece3.9562

PubMed

Other URL： https://onlinelibrary.wiley.com/doi/abs/10.1002/ece3.9562

Authorship：Last author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Cooperative breeding, a social system in which offspring receive care from other group members as well as their parents, occurs in insects, fish, birds and mammals. In this study, we report a new example of cooperative breeding in the cichlid fish (Neolamprologus bifasciatus). This species, endemic to Lake Tanganyika, Africa, inhabits rocky areas at depths below 30 m. Observations of eight nests using underwater video cameras showed that one to six subordinates were present in the nests of breeding pairs. The subordinates shared shelters with juveniles and breeders and engaged in brood/territorial defence and nest maintenance (removing sand from the nest), albeit at a lower frequency than female breeders. The frequency of sand digging by subordinates and female breeders decreased as the number of subordinates in the group increased, suggesting that subordinates reduce the costs of nest maintenance for breeders. The male breeders seldom showed territorial defence and nest maintenance. Subordinates exhibited submissive behaviours towards dominant breeders and larger subordinates within their breeding group, indicating a dominance hierarchy among group members. Gonad examination revealed that the subordinates of both sexes were sexually immature, suggesting that they may not participate in reproduction. An aquarium experiment showed that juveniles become subordinates in their natal nest and participate in territory defence. We conclude that N. bifasciatus is a cooperative breeder, with social systems and subordinate roles similar to those observed in other cooperatively breeding cichlids.

DOI： 10.1111/eff.12658

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

A new species of grunt sculpin, Rhamphocottus nagaakii inhabiting the northwestern Pacific, previously identified as Rhamphocottus richardsonii Gunther 1874, is described based on genetic evidence and morphological differences. The new species can be distinguished based on morphometric characters related to the head, including head length [45.3-54.6% of standard length (SL)], postorbital head length (18.8-25.5% SL) and the length of pectoral-fin base (15.8-20.7% SL), which are smaller than in R. richardsonii (53.6-60.5% SL, 26.2-31.7% SL, and 19.5-25.2% SL, respectively). Genetic differences between two species markedly exceed levels for intra-specific differences. Rhamphocottus nagaakii is considered to have arisen from a common ancestor of the two species, which probably inhabited somewhere the North Pacific Rim around the Aleutian Archipelago. During a period of cooling in the Pliocene or the Miocene, R. nagaakii and R. richardsonii became separated to the southern regions of the northwestern and northeastern Pacific, and subsequently underwent speciation.

DOI： 10.1007/s10228-022-00885-y

Authorship：Last author,　Corresponding author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Cooperative breeding systems, where individuals other than parents assist in raising offspring, have been documented in insects, fish, birds, and mammals. Still, the factors driving the evolution of such complex systems are not fully understood. Here, we report a new example of cooperative breeding in the obligate shell-brooding cichlid fish Neolamprologus meeli from Lake Tanganyika. Field observations revealed that dominant males were either monogamous or polygynous, with each mating with one to four dominant females. Dominant females maintain nests containing one to ten empty gastropod shells used as breeding substrates and shelters. Up to four immature subordinates of either sex lived in these nests. They assisted with territory defense and nest maintenance, the frequency of which was not different from that of the dominants. Parentage analyses showed that most subordinates were the offspring of at least one of the breeders, suggesting that juveniles delay dispersal and help in raising their relatives. The relatedness of subordinates to the breeders declined with increasing body size and was significantly higher to female than to male breeders. These patterns could be caused by extra-pair paternity, between-group dispersal of helpers, or sex differences in breeder turnover. Male helpers were larger than female helpers, and six out of eight dispersed individuals were females, suggesting female-biased dispersal. Because N. meeli is phylogenetically distinct from other cooperatively breeding cichlids, these results contribute to a better understanding of cooperative breeding in fishes and to understanding of the evolution of complex social systems in general.

DOI： 10.1007/s00265-022-03201-w

Repository URL： http://hdl.handle.net/10466/0002000409

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

An animal that tries to remove a mark from its body that is only visible when looking into a mirror displays the capacity for mirror self-recognition (MSR), which has been interpreted as evidence for self-awareness. Conservative interpretations of existing data conclude that convincing evidence for MSR is currently restricted to great apes. Here, we address proposed shortcomings of a previous study on MSR in the cleaner wrasse Labroides dimidiatus, by varying preexposure to mirrors and by marking individuals with different colors. We found that (1) 14/14 new individuals scraped their throat when a brown mark had been provisioned, but only in the presence of a mirror; (2) blue and green color marks did not elicit scraping; (3) intentionally injecting the mark deeper beneath the skin reliably elicited spontaneous scraping in the absence of a mirror; (4) mirror-naive individuals injected with a brown mark scraped their throat with lower probability and/or lower frequency compared to mirror-experienced individuals; (5) in contrast to the mirror images, seeing another fish with the same marking did not induce throat scraping; and (6) moving the mirror to another location did not elicit renewed aggression in mirror-experienced individuals. Taken together, these results increase our confidence that cleaner fish indeed pass the mark test, although only if it is presented in ecologically relevant contexts. Therefore, we reiterate the conclusion of the previous study that either self-awareness in animals or the validity of the mirror test needs to be revised.

DOI： 10.1371/journal.pbio.3001529

PubMed

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

In this study, the authors report the first record of egg masses deposited in solitary tunicates by the snubnose sculpin, Orthonopias triacis, from the Northeastern Pacific. Four egg masses were discovered in the tunicate Ascidia ceratodes that were genetically determined to be O. triacis. Female O. triacis had long ovipositors that allow deposition of their eggs inside the atrium of the tunicates. A comparison of host-tunicate size with ovipositor length of sculpins from the Northwestern Pacific, including the genera Furcina and Pseudoblennius, revealed that O. triacis had shorter ovipositors and spawned in the atrium of smaller species of tunicates. Ancestral state reconstruction of egg deposition in solitary tunicates using 1.86Mbp RNAseq data of 20 sculpin species from Northeastern and Northwestern Pacific revealed that this unusual spawning behaviour may have evolved convergently in different species occurring in the Northeastern vs. the Northwestern Pacific.

DOI： 10.1111/jfb.14920

PubMed

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Memorizing dominance relationships can help animals avoid unwinnable subsequent contests. However, when competitive ability changes over time—for example, as a function of condition—it may be adaptive to “forget” these dominance relationships and for subordinates to once again enter contests with previously dominant individuals. Here, we examined the behavior of pairs of male cichlid fish, Julidochromis transcriptus, in repeated contests separated by different time intervals. We found that the time taken to reach resolution of dominance relationships influenced subsequent aggressive behavior of the subordinate toward the dominant, with longer initial contests leading to higher subsequent aggression. Longer time intervals between contests also increased aggression from the subordinate toward the dominant. These results are consistent with increasing uncertainty due to ambiguous contest outcomes and increasing time intervals. Our results also show that a longer time was necessary to resolve contests between larger pairs, suggesting a self-assessment strategy, but not a mutual assessment strategy. Taken together, larger individuals appear to adaptively lose or ignore previously gathered social information because they have a higher fighting ability and better body condition. Therefore, we conclude that losing or ignoring unreliable information may be an adaptive strategy in the context of dominance relationships.

DOI： 10.3389/fevo.2021.685907

Authorship：Last author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Siblings often compete for limited resources, such as food provided by their parents. However, although several functions of nonlethal sibling (nonsiblicidal) aggression have been proposed, there is currently little empirical evidence for these, apart from food monopolization. Here, we investigated the functions of nonlethal sibling aggression in the biparental-caring territorial herbivorous cichlid Varibilichromis moorii. We found that the juveniles of this species are highly aggressive and that larger juveniles are more aggressive toward their smaller siblings. Larger juveniles feed on algae more frequently than smaller siblings, thereby indicating a dominance hierarchy. Sibling aggression decreased when algae in the nest was experimentally removed. Furthermore, the removal of smaller juveniles decreased sibling aggression among the remaining larger juveniles, whereas the removal of larger juveniles increased aggression among smaller juveniles. The algal feeding rate of juveniles only increased when larger individuals were removed from the nest. Moreover, larger juveniles attained higher growth rates and remained in natal nests longer than smaller individuals. Our results indicate that sibling aggression may facilitate the monopolization of resources by larger juveniles and extend the parental care period. Interestingly, a small subset of juveniles was observed to migrate to other nests. These juveniles were larger than those of the host brood, and their growth rate increased within the new nests. We suggest that subordinate juveniles may disperse from natal nests and sneak into new nests to enhance their rank, which may represent a novel example of a “best of a bad job” strategy associated with sibling competition.

DOI： 10.1093/beheco/araa150

Authorship：Last author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Baikal sculpins are a unique group of fishes, including both externally and internally fertilizing species. Sperm traits, such as morphology and motility, are predicted to undergo adaptive changes due to species fertilization modes. However, studies exploring such traits in Baikal sculpins are lacking. Here, we conducted a field study and investigated sperm traits of three sculpins with external fertilization (Cottocomephorus grewingkii, Leocottus kesslerii and Paracottus knerii) and one sculpin with internal fertilization (Comephorus dybowskii). Sperm head morphology was spherical in both types of fertilizing species; however, the head cross-sectional area of the sperm of the internal fertilizer was smaller than that of external fertilizers. This result implies that sperm head morphology might be adapted to swim in a viscous ovarian fluid. The internal fertilizer, C. dybowskii, had longer and faster-swimming sperms with longer motility duration than the external fertilizers, perhaps due to different sperm competition levels. Sperms of the internal fertilizer were only motile in isotonic solutions, whereas sperms of the external fertilizers were motile in lake waters, suggesting that sperm motilities are specialized according to their external/internal environments. To our knowledge, this is the first study to demonstrate sperm traits of Baikal sculpins, which may have evolved adaptively along with changing fertilization modes.

DOI： 10.1111/jzo.12867

Other URL： https://onlinelibrary.wiley.com/doi/full-xml/10.1111/jzo.12867

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Human society is cooperative and characterized by spontaneous prosociality. Comparative studies on endotherm vertebrates suggest that social interdependence causes the evolution of proactive prosociality. To test the generality of this hypothesis, we modify a prosocial choice task for application to the convict cichlid, Amatitlania nigrofasciata, a monogamous fish with biparental care and a strong pair bond. We also affirm that male subjects learn to favor prosocial choices when their mates are the recipients in a neighboring tank. When the neighboring tank is empty, males choose randomly. Furthermore, in the absence of their mates, males behave prosocially toward a stranger female. However, if the mate of the subjects is also visible in the third tank, or if a male is a potential recipient, then subjects make antisocial choices. To conclude, fish may show both spontaneous prosocial and antisocial behaviors according to their social relationships with conspecifics and the overall social context.

DOI： 10.1038/s41467-021-22075-6

PubMed

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Maintaining a certain number of spawning grounds for endangered fish is particularly important in rivers and streams where the environment changes drastically through floods and exploitations. Ryukyu-ayu Plecoglossus altivelis ryukyuensis is an endangered annual fish inhabiting the few streams and rivers flowing through the Amami-Oshima Island, southern Japan, and spawns in the lower reaches at sites with the specific riverbed conditions. In the island, resident volunteers along with researchers modify riverbed manually to provide conditions suitable for the natural spawning of the fish every year. This study investigated the effects of these activities on the riverbed conditions and consequently on the spawning by Ryukyu-ayu in two rivers. Our results showed that riverbed hardness and the amount of silt significantly decreased in the modified areas, but not in the adjacent unmodified areas. In one of the two rivers, the modification suppressed the settlement of net-spinning caddisfly larvae Stenopsyche schmidi that promote consolidation of the riverbed. The riverbed conditions in the modified areas were similar to those in the sites where P. a. ryukyuensis indeed spawned. These results suggest that manual modification is efficient in improving riverbed conditions for the spawning of Ryukyu-ayu. However, the eggs of the fish were not found at the modified areas in both rivers. It will be necessary to develop effective and practical ways of selecting sites for modification without obstructing the natural spawning in this fish.

DOI： 10.1007/s10228-020-00745-7

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Surfperches (Embiotocidae) are a unique family of viviparous fishes that have internal fertilization, gestation to the sub-adult stage, and live-birth; therefore, maternal investment is extremely high. This invokes the expectation that brood size is limited and females should be choosy and select few mates. Yet multiple paternity occurs in all eight species examined to date, with high prevalence ranging from 92–100%. Most surfperches are found along the Eastern Pacific coast, but Ditrema temminckii is distributed in the Western Pacific and we found differences in their mating strategy compared to other surfperches. In D. temminckii, prevalence of multiple paternity was only 60%. Further, the average number of sires was only 1.86 per brood even though brood sizes ranged from 12–45, and paternity was skewed, with the majority of paternity allocated to a single male. We propose that these differences may be associated with strong female selection on males in this species. Finally, we evaluated whether the number of fathers is an accurate estimate for the number of mates by comparing the number of alleles detected from fathers within the brood to the number of alleles from mates via genotyping alleles from spermatozoa within the uterine sac and found no significant difference, suggesting that the number of sires is a reasonable estimate for the number of mates in D. temminckii.

DOI： 10.1643/CE-19-271

Authorship：Last author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Sperm production is costly, and males are expected to strategically allocate this potentially limiting resource to maximize their fitness. Sperm allocation theory predicts that males should adjust their sperm expenditure in relation to female quality. However, the available empirical evidence is limited. In this study, we assessed whether wild male medaka (Oryzias latipes) would allocate their sperm depending on female quality under controlled conditions. Behavioral observations revealed that spawning behavior could be classified into four stages: male quivering, female quivering, sperm release, and stay. Of these behaviors, only the duration of sperm release was positively correlated with the number of sperm ejaculated in the aquarium, suggesting that males may adjust the sperm number expended for each mating by controlling the duration of sperm release. The estimated amount of sperm released per spawning was positively and significantly correlated with the body depth and weight of paired females. This result is consistent with the prediction arising from the sperm allocation hypothesis, and suggests that male medaka may allocate their sperm depending on paired female body depth and weight. However, the number of released sperm did not correlate with the number of spawned eggs, which was positively correlated with body depth and weight of females. These results imply that medaka females may have counter-strategies against sperm allocation by males, and consequently, males might not be able to adjust the number of sperm efficiently. We disscuss our results from the perspective of sexual conflict over sperm as a limited resource.

DOI： 10.2108/zs190132

PubMed

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Although parental care is known to occur in a wide range of teleost fishes, postnatal provisioning of nutrition has been documented rarely. Here, we describe a novel example of bi-parental care in a teleost, i.e. mucus-provisioning behaviour in the scale-eating cichlid Perissodus microlepis endemic to Lake Tanganyika. Field observations revealed that young guarded by their parents frequently glanced towards the body surface of both parents. Furthermore, analyses of stomach contents of the young found the presence of ingested mucus, confirming that the young feed on the mucus secretions of their parents. The frequency of glancing behaviour increased with size of the young up to similar to 13 mm in standard length, but then declined with further growth. Additionally, the frequency of glancing of young towards their parents was higher when the frequency of foraging on plankton was lower. Underwater cage experiments revealed a higher rate of growth in the young kept in direct contact with their parents than in those not allowed direct contact. We conclude that glancing behaviour in young P. microlepis is a form of direct parental nourishment that confers growth benefits to the young when food abundance is low.

DOI： 10.1093/biolinnean/blz124

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

DOI： 10.1111/eth.12929

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Interspecific interactions between parasites and hosts can influence the evolution of behavioural and morphological adaptations of both parasites and their hosts. There is, however, little empirical evidence available regarding the evolution of reproductive traits driven by these interactions. In this paper, we investigated host selection and ovipositor length in nine sympatric marine sculpins that oviposit into tunicates or sponges. Field and genetic studies have revealed host use for eight out of nine species of sculpins investigated here: five species of Pseudoblennius, two species of Furcina and one species of Vellitor. For one species studied (V. minutus), no egg masses could be found. Ovipositor length reflects morphology of host species utilised: six sculpin species had extremely long ovipositors allowing females to attach eggs to the deep atrium of solitary tunicates, whereas the two species that attached their eggs to the small space of atrial siphon of colonial tunicates and the spongocoel of sponges had short ovipositors. Ovipositor length varied between solitary-tunicate spawners and species with longer ovipositors selected larger tunicates. Since the ancestral form is non-parasitic, the ovipositor evolved as an adaptation to utilise sponges and tunicates as hosts. Sculpins found sympatrically may show host specificity to avoid interspecific competition for spawning niches and ovipositors may have evolved depending on the species and size of host invertebrates.

DOI： 10.1007/s00227-019-3506-4

Other URL： http://orcid.org/0000-0003-3254-7943

Authorship：Last author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Sperm fixation in better conditions is a requisite for the examination of sperm morphology using optical microscopes. Here, we investigated the effects of different fixatives on sperm morphological characteristics in four marine fishes: copulatory sculpins Pseudoblennius marmoratus and Radulinopsis taranetzi, and non-copulatory sculpin Icelus mororanis and dragonet Repomucenus beniteguri. We found that a 2.5% glutaraldehyde solution is optimal for observing sperm morphology in these fishes. Furthermore, the low concentrations (2.5%) of formalin could be useful, but the solvent for diluting formalin should be changed depending on the species: seawater in copulatory and non-copulatory sculpins and isotonic solution in the non-copulatory dragonet.

DOI： 10.1007/s10228-018-0672-1

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Siblings often compete for limited resources, particularly food provided by their parents. Such competition is usually nonviolent, but direct aggression has evolved in some species. However, there is little knowledge about sibling aggression in species without parental provisioning. Here, we investigated sibling aggression in the cichlid Neolamprologus furcifer in Lake Tanganyika, Zambia. In this species, females guard their broods in the nest but do not provide any food. Early-stage fry did not show any sibling aggression while foraging on plankton, but began to show nonlethal aggression once they started to forage on small benthic shrimp at 2weeks of age. The frequency of sibling aggression decreased at week 7, when the density of fry decreased remarkably. Sibling aggression also decreased following a short-term increase in food through supplemental feeding. The aggression was higher in the morning than in the afternoon despite higher abundance of shrimp at that time, and decreased when the number of shrimp in the nest was experimentally reduced. These results indicate that food availability affects sibling aggression of animals that do not exhibit parental provisioning.

DOI： 10.1007/s10750-018-3768-8

Other URL： http://link.springer.com/content/pdf/10.1007/s10750-018-3768-8.pdf

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Many cichlid species in the shallow-shore of Lake Tanganyika suffer damage from attacks by the scale-eater Perissodus microlepis. Many prey fish engage in warning behaviors to this predator. It has been hypothesized that, if prey fish have difficulty employing such behavioral tactics, morphological defenses against scale-eating, such as hard scales, will evolve. The shrimp-eating cichlids, Altolamprologus compressiceps (Ac) and Neolamprologus fasciatus (Nf), exhibit hunting behaviors in which they remain motionless for up to 10 seconds while aiming at prey, when they are vulnerable to scale-eating predators; thus, these fish have likely evolved morphological defenses against "scale-attacks". We tested this hypothesis in Ac and Nf, as well as three other predatory fish, Lamprologus callipterus, Lepidiolamprologus elongatus and Lep. attenuatus, that are not motionless for such a long time. Under natural conditions, Ac and Nf were rarely attacked, while the other three species were attacked frequently. When freshly killed specimens of these five species were displayed underwater in the presence of P. microlepis, Ac was rarely attacked, while Nf and the three other species were attacked frequently. Among the five fish species, the force required to tear off scales was highest for Ac, and this force was negatively correlated with the frequency of attacks on the displayed fish. These results support the hypothesis that the hard scales of Ac function as an anti-scale-attack measure, although it remains unclear why free-swimming Nf were rarely attacked while aiming at prey, despite the fact that the force required to tear off its scales was not large.

DOI： 10.2108/zs180130

PubMed

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

The ability to perceive and recognise a reflected mirror image as self (mirror self-recognition, MSR) is considered a hallmark of cognition across species. Although MSR has been reported in mammals and birds, it is not known to occur in any other major taxon. Potentially limiting our ability to test for MSR in other taxa is that the established assay, the mark test, requires that animals display contingency testing and self-directed behaviour. These behaviours may be difficult for humans to interpret in taxonomically divergent animals, especially those that lack the dexterity (or limbs) required to touch a mark. Here, we show that a fish, the cleaner wrasse Labroides dimidiatus, shows behaviour that may reasonably be interpreted as passing through all phases of the mark test: (i) social reactions towards the reflection, (ii) repeated idiosyncratic behaviours towards the mirror, and (iii) frequent observation of their reflection. When subsequently provided with a coloured tag in a modified mark test, fish attempt to remove the mark by scraping their body in the presence of a mirror but show no response towards transparent marks or to coloured marks in the absence of a mirror. This remarkable finding presents a challenge to our interpretation of the mark test-do we accept that these behavioural responses, which are taken as evidence of self-recognition in other species during the mark test, lead to the conclusion that fish are self-aware? Or do we rather decide that these behavioural patterns have a basis in a cognitive process other than self-recognition and that fish do not pass the mark test? If the former, what does this mean for our understanding of animal intelligence? If the latter, what does this mean for our application and interpretation of the mark test as a metric for animal cognitive abilities?

DOI： 10.1371/journal.pbio.3000021

PubMed

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Scale-eating cichlid fishes, Perissodus spp., in Lake Tanganyika have laterally asymmetrical bodies, and each population is composed of righty and lefty morphs. Righty morphs attack the right side of prey and lefty morphs do the opposite. This anti-symmetric dimorphism has a genetic basis. Temporal changes in the frequencies of morphs in two cohabiting scale-eating species (Perissodus microlepis and P. straeleni) were investigated over a 31-year period on a rocky shore at the southern end of the lake. Dimorphism was maintained dynamically during the period in both species, and the frequencies oscillated with a period of about four years in a semi-synchronized manner. Recent studies have indicated that this type of anti-symmetric dimorphism is shared widely among fishes, and is maintained by frequency-dependent selection between predator and prey species. The combinations of laterality in each scale-eater and its victim were surveyed. The results showed that “cross-predation”, in which righty predators catch lefty prey and lefty predators catch righty prey, occurred more frequently than the reverse combination (“parallel-predation”). The cause of the predominance of cross-predation is discussed from the viewpoint of the physical and sensory abilities of fishes.

DOI： 10.3390/sym11010119

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Unravelling the evolution of complex social organization in animals is an important aim, not least because it helps to understand the evolutionary roots of human sociality. Recent advances in comparative methods allow to approach this question in a phylogenetic context. The validity of such comparative approaches depends strongly on the quality of information regarding the behaviour, sociality, and reproduction of animals in natural systems, and on the quality of the phylogenetic reconstruction. Applying a novel comparative approach, a recent study of Dey et al. (, Nature Ecology & Evolution, 1, 137) concluded that evolutionary transitions to cooperative breeding in cichlid fishes were not associated with the social mating pattern. Here we argue that this result was adversely affected by equivocal classifications of mating patterns, and inadequate phylogenetic data. In order to illustrate the impact of the mating system misclassifications, we scored mating patterns as reported in the original literature and re-analysed the dataset based on Dey et al.'s tree topology. The result suggests that the mating system does in fact significantly explain the evolutionary transition to cooperative breeding in lamprologine cichlids, but we submit that a reliable conclusion cannot be reached before improving the behavioural information and the underlying phylogenetic reconstruction. The problems identified in this case study are not unique and we urge caution in the interpretation of results from comparative phylogenetic studies in general. We do agree with Dey et al. () though that the lamprologine cichlids of Lake Tanganyika may constitute a fundamental test case for the theory of social evolution, but better information on their behaviour and phylogenetic relationships is needed to allow meaningful analyses.

DOI： 10.1111/eth.12813

Authorship：Last author   Publishing type：Research paper (bulletin of university, research institution)   Kind of work：Joint Work   International / domestic magazine：Domestic journal  

J-GLOBAL

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Animals in a population consistently differ from one another in behavioural types over time and this difference can affect intra- and interspecific relationships. However, empirical studies about roles of behavioural individual variation in interspecific interactions are scarce. Here, we provide evidence that inter-individual variation of a cichlid in aggression affects access to its territory by a heterospecific cichlid. In Lake Tanganyika, a zoobenthivorous cichlid Neolamprologus mustax (Nm) is admitted into territories of an algivorous Variabilichromis moorii (Vm) to prey on benthic invertebrates, while other zoobenthivorous fishes are chased from the territories. We conducted an experiment in which caged Nm fish were exposed twice to each Vm fish in natural habitats. Results indicated repeatable individual variations in Vm aggression towards Nm. Moreover, diving observations indicated that Nm fish frequently used some of Vm territories inside their own territories, but rarely or never used others. This uneven use of Vm territories by the Nm fish was negatively correlated with individual variations in Vm aggression. We conclude that the preferential access of Nm to Vm territory is gained by Nm's recognising more tolerant Vm fish or discriminating among sites for their territories.

DOI： 10.1007/s10750-016-2822-7

Publishing type：Research paper (bulletin of university, research institution)  

J-GLOBAL

Publishing type：Research paper (bulletin of university, research institution)  

J-GLOBAL

Publishing type：Research paper (bulletin of university, research institution)  

J-GLOBAL

Publishing type：Research paper (scientific journal)   Kind of work：Single Work  

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

CiNii Article

J-GLOBAL

Authorship：Last author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Two chaenopsid fishes, Neoclinus chihiroe and Neoclinus lacunicola, were collected from Sadogashima Island, the Sea of Japan. The collected specimens represent the northernmost records of the two species and the first voucher specimens from the Sea of Japan. Morphological information and colour photographs, including underwater photos, of these specimens were provided. Additional photographic evidence from Tobi-shima Island, ~100 km north-north-east of Sadogashima Island, further extended the northernmost record of Neoclinus lacunicola.

DOI： 10.1017/S1755267215001037

Publishing type：Research paper (scientific journal)  

CiNii Article

J-GLOBAL

Publishing type：Research paper (scientific journal)  

Cooperative breeding has been studied intensively in many species of birds and mammals but remain less well studied in fish. We report a remarkable new example of a cooperatively breeding cichlid from Lake Tanganyika, Neolamprologus obscurus. Using field observations and microsatellite DNA analyses, we studied group structure, helping behavior, relatedness, and dispersal of this species. We present four major observations. First, large territorial breeding males mated with one to eight breeding females, each of which was territorial and unrelated to another. Second, one to ten smaller fish ("subordinates") of both sexes were allowed to stay inside the breeding females' territories. Subordinates were often highly related to both the respective breeding male and female and performed territory defense and shelter maintenance, which is regarded as helping behaviors. Third, one to three subordinate males, similar in size to breeding females, were allowed to stay inside a breeding male's territory but were not tolerated in the breeding females' territories. Pairwise relatedness suggests these individuals are usually sons of the respective breeding male. Fourth, pairwise relatedness estimates suggest that juveniles delay dispersal and assist their mothers in raising offspring. As female subordinates grow up, they leave the father's territory and disperse into other groups. In contrast, male subordinates leave their mother's territory but remain within the territory of their father. The described social system makes N. obscurus a promising new model species to study the evolution of cooperative breeding.

DOI： 10.1007/s00265-014-1830-8

Publishing type：Research paper (scientific journal)   Kind of work：Single Work  

DOI： 10.2331/suisan.81.871

CiNii Article

Publishing type：Research paper (scientific journal)  

DOI： 10.3389/fevo.2015.00085

Publishing type：Research paper (scientific journal)  

We investigated the evolutionary relationship between spawning behaviour and sperm motility traits among Tanganyikan mouth-brooding cichlid species that have developed diverse mating behaviours and male sexual traits. Mouth-brooding behaviour is common among these fish, but different species demonstrate a range of spawning behaviours, bower construction, male sexual traits and timing of gamete release. We observed spawning behaviours and compared sperm motility traits of 28 Tanganyikan mouth-brooding cichlids to elucidate the evolutionary correlations between these traits. Sperm longevity was considerably longer in bower-building species that construct crater-shaped spawning sites compared with species that do not build bowers. Male bower builders released sperm in the pit of the bower prior to spawning, and the time from ejaculation to fertilization was longer. Conversely, most mouth-brooding cichlids deposited semen directly into the female buccal cavity, and spawned eggs were immediately picked up to be placed inside the cavity
thus, the time from ejaculation to fertilization was short. These observations suggest that increased sperm longevity is favoured in bower builders. Comparative phylogenetic analyses suggested that bower-building behaviour and greater time from ejaculation to fertilization are associated with the extension of sperm longevity, whereas sperm competition rank does not play a major role. In addition, bower-building behaviour preceded the emergence of increased sperm longevity. These results indicate that the extension of sperm longevity as a result of the emergence of bower builders may have acted as an evolutionary attractor for sperm longevity.

DOI： 10.1111/jeb.12522

PubMed

Publishing type：Research paper (scientific journal)  

Changes in mRNA levels of prolactin (PRL) during the upstream migration were examined in fry of the amphidromous fish, ayu Plecoglossus altivelis. Quantification of mRNA has been done with real-time PCR and expressed as whole body or pituitary contents depending the body size of fry. PRL mRNA levels of ayu caught in seawater of the coastal area remained low during early spring. Prior to the start of the upstream migration, the fish caught in the coastal area in mid spring showed increased levels of PRL mRNA. There were further increases in PRL levels in the fish caught in the river. Analysis of proportions revealed that there were significant differences among PRL mRNA in the fish caught in different environmental salinities. Body weight showed a positive relation with PRL mRNA in ayu caught in seawater. A landlocked population of ayu, which migrates from lake to river, showed no significant change in PRL mRNA levels before and after upstream migration. Results in this study indicate the importance of up-regulation of PRL gene expression of ayu during the upstream migration from seawater to fresh water. There is a possible relationship between body size and PRL in the early developmental stage of ayu in seawater, but not in the fish in fresh water. © 2014 Zoological Society of Japan.

DOI： 10.2108/zs130181

PubMed

Publishing type：Research paper (scientific journal)  

DOI： 10.1111/jzo.12125

Publishing type：Research paper (scientific journal)  

To examine how territorial males counter reproductive parasites, we examined the paternity of broods guarded by territorial males using 5 microsatellite loci and factors that determine siring success in a wild population of the Lake Tanganyika cichlid Lamprologus lemairii. Females enter rock holes (nests) and spawn inside, and territorial males release milt over the nest openings. Sneakers attempt to dart into the nests, but territorial males often interrupt the attempt. The body size of territorial males (territorial defense ability) and the size of nest opening (the ability to prevent sneakers from nest intrusions) are predicted to be factors that affect paternity at the premating stage, whereas milt quality traits are factors that affect paternity at the postmating stage. Parentage analyses of 477 offspring revealed that most clutches have few or no cuckolders, and territorial males sired > 80% of eggs in 7 of the 10 analyzed clutches. Larger territorial males that spawned in nests with narrower openings had greater siring success. In contrast, none of the milt traits affected the siring success. These suggest that territorial male L. lemairii adopt premating strategies whereby they effectively prevent reproductive parasitism.

DOI： 10.1093/jhered/esu009

PubMed

Publishing type：Research paper (scientific journal)  

Stream fish with low mobility are often restricted to a narrow range of a stream course, and their morphological characters tend to be affected substantially by the environmental conditions of their habitat. We examined the relationships between environmental conditions and morphological characters of Japanese fluvial sculpin (Cottus pollux), a small, benthic fish with low mobility, at seven tributaries of the same river system in eastern Japan. Discriminant function analysis (DFA) indicated significant morphological differences in sculpins amongst the seven tributaries, and over 80% of individuals were classified correctly in each tributary.The strong positive correlation/loadings on the first discriminant function (DF1: 49.9% of total variation) were anterior caudal peduncle depth (0.436) and caudal peduncle truss (0.387), both of which could be regarded as an attribute of caudal peduncle depth. The second discriminant function (DF2: 16.5% of total variation) had a high negative loading for distance between the posterior first dorsal fin and anterior anal fin (-0.454), which could be regarded as an attribute of body depth. Correlation analysis indicated that sculpin tended to have a lower caudal peduncle depth under faster bottom current velocities at the tributary scale. Individuals deviating substantially from the centroid of DF2 in each tributary had a poorer body condition. Our results suggest the possibility of changes in the morphological characters of Japanese fluvial sculpin in relation to environmental conditions even at the tributary scale within the same river system.

DOI： 10.1111/eff.12045

Publishing type：Research paper (scientific journal)  

In species with alternative reproductive tactics (ARTs), males employing different tactics usually have different appearance. The clearest difference is body size: bourgeois males that monopolize access to females are larger than sneaker males that steal fertilizations from them. Sneakers are also known to be often dull in colour compared with bourgeois males and rather resemble females. However, this typical colour pattern is unlikely in the Lake Tanganyika cichlid Neolamprologus mondabu: we observed sneaking by two distinctive colour morphs, namely, black (which is apparently conspicuous against the background) and white (which is apparently background-matching). Because breeding females are black, this observation indicates that one type of sneakers contrasts female appearance. In this study, we conducted field studies to determine the expression of body colour in relation to ARTs in this fish. Body colour was dependent on size, but not sex and maturation, with black individuals being larger than white ones. Together with the presence of intermediate grey colour expressed by intermediate-sized individuals, this fish could ontogenetically changes their body colour from white to black. Both sexes of black individuals occupied feeding territories, but white individuals were non-territorial, indicating that the black body signals the possession of a feeding territory. Sexually active females were invariably black, whereas sexually active males were both black and white in colour. Few of the largest black males held harems, which included several female territories, whereas the remaining males were bachelors with no female territories. These bachelor males invested more in testes than harem males, suggesting that bachelors employ sneaking tactics, which is corroborated by our sneaking observations. To our knowledge, this is the first study showing that sneakers are entirely dissimilar to females in appearance. Herein, we discuss why sneakers are dichromatic in relation to their life histories. © 2014 The Zoological Society of London.

DOI： 10.1111/jzo.12125

Publishing type：Research paper (scientific journal)  

In Japanese streams fishermen often give children the opportunity to enjoy natural environments by allowing them to participate in such activities as releasing fish stock and creating spawning sites, as well as by conducting habitat preservation activities, fishing schools and nature observation tours. This study assessed the educational significance of fishermens activities involving schoolchildren using a questionnaire survey of men and women at least 20 years old who were attending an exhibition at the Nikko Laboratory of the National Research Institute of Fisheries Science in August 2010. More than 70% of the respondents acknowledged the educational significance in the people–nature relationship and mental/psychological aspects of such activities; women evaluated the significance of such activities more positively compared with men. In the social life aspect, less than 50% of the respondents acknowledged being motivated to engage in freshwater fisheries activities and to settle in the local community. Meanwhile over 70% thought the activities would improve the appreciation of freshwater fisheries and the local community and inform the value of labor and cooperation. The results suggest most people appreciate the contribution of these fishermens activities in the education of children.

DOI： 10.3739/rikusui.74.165

CiNii Article

Publishing type：Research paper (scientific journal)  

It is important to select the most appropriate method for fish sampling in streams and rivers
the sampling efficiency as well as any negative effect of the method of fish sampling on fishes such as stress, injury, and mortality must be considered. This study aimed to investigate stress hormone responses in ayu Plecoglossus altivelis in reaction to direct current (DC) electrofishing, alternating current (AC) electrofishing, and cast netting in artificial streams. The mortality, injury rate, and catch efficiency of these catching methods were also compared. It was found that immediately after capture, fish caught using a cast net exhibited significantly higher cortisol levels than did control fish that were caught rapidly by a hand net. Cortisol levels did not differ between electroshocked fish and the controls. Time required to catch 12 fish was shorter when DC was used (20 s) than when AC was used (45 s). The time required to catch fish greatly increased when a cast net was used (840 s). Cortisol levels in DC electroshocked and control treatment groups were at resting levels 24 and 48 h after capture. However, higher cortisol levels were found in fish captured using a cast net at both these time points. Cortisol levels in AC electroshocked fish returned to lower levels at 24 h, but increased again at 48 h. Furthermore, 48 h following capture, the fish caught by AC electrofishing exhibited higher mortality (7. 5 %) than those captured by other methods (0 %). Spinal injury was also detected in one of the fish in this group. Considering these findings, DC electrofishing is the most effective and least damaging method for collecting P. altivelis in streams with respect to stress, physical damage, and efficiency. © 2013 The Japanese Society of Fisheries Science.

DOI： 10.1007/s12562-012-0592-3

Publishing type：Research paper (scientific journal)  

Social and foraging modes in fish often vary between individuals with different body sizes and between populations under different ecological conditions. We studied social and foraging behaviour of algae-grazing fish Plecoglossus altivelis ryukyuensis (Ryukyu-ayu) inhabiting Japanese subtropical island streams. Ryukyu-ayu exhibited four behavioural modes: territorial, schooling, solitary and floating. Their body sizes differed among these modes. Territorial fish predominantly foraged on benthic algae, whereas schooling and solitary individuals frequently consumed drifting materials as well. Schooling fish were smaller than territorial fish, but, unlike some other algae-grazing fish species, did not use schooling to gain access to food within territories. Territorial fish attacked smaller conspecifics but exhibited lateral display towards larger fish and schooling fish while occasionally attacking grazing gobies. Larger fish maintained larger feeding territories and occupied territories for longer periods than smaller fish did. This suggests that, in Ryukyu-ayu, intra- and interspecific food competitions and relative body size can influence diverse behavioural modes and duration of territory occupation. We also found that Ryukyu-ayu foraged more often and had larger feeding territories than ayu P. a. altivelis inhabiting temperate streams. We conclude that foraging strategies of Ryukyu-ayu may have adapted to subtropical island streams, where algal productivity is much lower than that in temperate regions. © 2011 John Wiley &amp
Sons A/S.

DOI： 10.1111/j.1600-0633.2011.00517.x

Publishing type：Research paper (scientific journal)   International / domestic magazine：Domestic journal  

The asymmetry of mouth morphology, in which the mouth opens either leftward or rightward, is a unique example of antisymmetry that is widely found in fishes, such as Tanganyikan scale-eating cichlids, herbivorous cichlids, and the Japanese freshwater goby. This dimorphism is thought to be heritable in a Mendelian manner similar to that of the dominance of the lefty allele over righty, with homozygotes of lefty alleles being absent. This study aims to reveal whether this trait is inherited in the same Mendelian manner in fishes other than those examined to date, and whether the absence of the dominant homozygote is due to a lethal effect. We conducted F(1) and F(2) breeding experiments using the Tanganyikan cichlid Julidochromis transcriptus and Japanese medaka Oryzias latipes. For both J. transcriptus and O. latipes, the F(1) generations produced by incrossing lefty parents showed a lefty:righty ratio of 2:1, whereas incrosses of righties produced only righty offspring. Test crosses between lefty and righty produced a 1:1 ratio of lefty and righty offspring. These results are consistent with the inheritance model in which righty is homozygous for a recessive righty allele and lefty is heterozygous for dominant lefty and recessive righty alleles, in agreement with previous observations. The F(2) test cross also confirmed this pattern. Furthermore, no lethal effects on hatchability of O. latipes were detected, refuting the suggestion that the dominant homozygote is embryonic lethal. We conclude that mouth laterality is inherited in the same Mendelian manner in these two species, similar to that other fish species studied previously. However, the reason for absence of the dominant homozygote remains unclear.

DOI： 10.2108/zsj.29.49

PubMed

Publishing type：Research paper (scientific journal)  

An algivorous cichlid, Variabilichromis moorii (Vm), defends permanent territories in Lake Tanganyika, Africa. A zoobenthivorous cichlid, Neolamprologus mustax (Nm), spends 60% of daylight hours foraging in Vm territories, from which other zoobenthivorous fishes are chased out and consequently which are much richer in prey animals than areas outside of Vm territories. We conducted a field experiment to examine whether Nm residents and non-residents received different degrees of attacks from Vm. Nm fish were caught in their territories, released at a point distant from these territories, and followed to observe interactions with Vm fish. The frequency of attacks received by the displaced Not fish was greater than attacks received by Nm residents, indicating that Nm residents had easier access to Vat territories than non-residents did. A possible mechanism for this is reduced aggression of Vm towards Nm residents, as a result of the 'dear enemy' effect that has been reported in territorial contests between rivals. An alternative mechanism is that tolerance towards Nm differs among Vm fish and Nm residents selectively visit more tolerant Vat fish due to previous experience while non-residents randomly approach both tolerant and hostile Vat fish. The ability of Vat to discriminate between Nm residents and non-residents is essential to the former mechanism but not to the latter. To more specifically examine which mechanism works in the Vm Nm commensal system, we will need to follow individually identified Vat fish interacting with Nm residents and non-residents.

DOI： 10.1163/156853912X629139

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

Alternative reproductive tactics (ARTs) are found in several Lake Tanganyika shell-brooding cichlids. Field studies were conducted in the Wonzye population to examine reproductive ecology and ARTs in the Lake Tanganyika shell-brooding cichlid Neolamprologus brevis. We discovered that this fish occurred in both rocky- and sandy-bottom habitats, but in rocky habitats, brood-caring females exclusively occurred in shell-patches that another cichlid species created. All N. brevis of both sexes in the patches were sexually mature, whereas immature males and females with unripe eggs were found frequently in sandy-bottom habitats. Males in sandy-bottom habitats were smaller, but fed more frequently and were in better somatic condition than males in the patches. Similar tendency was found in females. This indicates that N. brevis uses different habitats depending on the stage of its life history, with migration from sandy-bottom habitats to the shell-patches for reproduction. Males in the patches exhibited different behavior patterns: floating above the patches and lying in the patches. The former was larger, more aggressive, and invested less in gonads (relative to body size) than the latter. These results accord with those of other shell-brooding Lake Tanganyika cichlids with ARTs, and they therefore suggest the presence of ARTs in N. brevis.

DOI： 10.1155/2012/193235

PubMed

Publishing type：Research paper (scientific journal)  

富山県庄川に生息するアユを対象に、最近の体サイズの動向を把握し、また、個体の成長に影響を及ぼす条件の解明を試みた。1990年代前期および2000年代後期の9月期の漁獲データを比較したところ、過去3年間は例年を下回る小型個体が優占したため、最近の体サイズにおける小型化傾向が実証された。耳石上の輪紋数をカウントしたところ、2010年級群には遅生まれの個体が多く、さらに、Sr／Caの経時変化から、遅い時期に河川を遡上した個体が多く認められた。個体間の体サイズ変異は、海中生活期間とは無関係に、河川生活期間の長短によって説明された。小型化傾向の引金要因には、早生まれ群を消滅させるような大規模災害の関与する可能性が指摘された。

CiNii Article

Publishing type：Research paper (scientific journal)  

It is well known that excessive suspended sediment (SS) negatively affects the fitness of fish by causing gill damage, lowered feeding efficiency, and physiological stress, all of which may impair growth, survival, and reproduction. Despite numerous researches on the effects of SS on fishes, few studies have examined its impact on stress hormone response. We conducted an experiment to test whether increased levels of SS elevate stress hormone levels in wild and low- and high-inbred hatchery strains of ayu Plecoglossus altivelis (Plecoglossidae) inhabiting clear rivers. We measured serum cortisol concentrations in fish exposed for 3. h to water with 200. mg/l of kaolin (SS treatment), fish exposed for 3. h to clear water (control treatment), and fish in stock tanks (initial control). Fish exposed to SS exhibited greater elevations in cortisol levels than control fish and initial controls. Control fish showed a small increase in cortisol levels compared with initial controls
this was probably because of the stress of handling and transfer to a novel environment. Stress response to SS in high-inbred strains was significantly lower than those in wild and low-inbred strains. These results suggest that SS is a significant environmental stressor that may increase the susceptibility of ayu to disease. Further, highly domesticated ayu may be maladaptive in nature because of lower reactivity of their stress axes as compared with those of wild or low-inbred strains. © 2011 Elsevier B.V.

DOI： 10.1016/j.aquaculture.2011.01.024

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

同時的雌雄同体であるサラサウミウシにおいて8遺伝子座のマイクロサテライトマーカーを開発した。これらのマーカーでは，一遺伝子座あたりの対立遺伝子数は1から30，平均が15と高い多型性が認められた。多型性を示す7遺伝子座のマーカーヘテロ接合度の実測値と予測値は，それぞれ0.409から0.905，0.518から0.960の範囲であった。以上，サラサウミウシの親子判定に使用可能と考えられる多様性の高いマイクロサテライトマーカーを特定した。

CiNii Article

Publishing type：Research paper (scientific journal)  

The effect of group size on reproductive success has long been studied in cooperatively breeding species, as it might provide an adaptive explanation for group-living in social species. Numerous studies have shown positive effects of subordinates on reproductive success ('helper effect'), but these studies have also revealed the importance of controlling statistically, or experimentally, for the effect of other factors that might affect reproductive success. Here, we first examine the relationships between group size, body size of group members and nest size in the cooperatively breeding cichlid Julidochromis ornatus, in which unrelated helpers frequently participate in reproduction and their breeding nests inside rock crevices may be crucial for reproduction and survival of all group members. Then, we subsequently investigate the relationship between group size and reproductive success, while controlling for these factors. The results showed that group size was significantly related to body size of group members rather than nest size
and larger breeders had larger helpers. It was found that group size significantly increased group reproductive output. More importantly, reproductive success of male breeders did not depend on the presence of mature helpers, whereas female reproductive success increased when two males assisted her and tended to decrease when two females bred cooperatively. We conclude that breeding groups of J. ornatus have size hierarchical societies that relate to group size, and group composition of genetically unrelated and co-breeding members affects their reproductive success. © 2010 Blackwell Verlag GmbH.

DOI： 10.1111/j.1439-0310.2009.01735.x

Publishing type：Research paper (scientific journal)  

To investigate seasonal changes in reproductive and physical condition, sexual dimorphism, and mating tactics in the jewelled blenny Salarias fasciatus, monthly collections were conducted on the fringing reef in northern Okinawa, Japan. Monthly variation in the female gonadosomatic index suggested that the breeding season of this species is from April to June. The physical condition and hepatosomatic index of both sexes considerably deteriorated during the course of the breeding season. Such declines may be primarily due to egg production in females and brood care in males. Males' elongated anal spines were longer than females', but no other apparent sexual dimorphisms were detected, indicating that S. fasciatus exhibits a low degree of sexual dimorphism. Examinations of testes size and the testicular gland area during the estimated breeding season revealed that the gonadosomatic index values of smaller males did not differ from those of larger males. This result may differ from other blenny species that exhibit alternative male reproductive tactics. However, patterns of male testicular glands of S. fasciatus were similar to those of other blennies with alternative tactics, i.e., smaller males had poorly developed testicular glands compared with larger males. © 2009 The Ichthyological Society of Japan.

DOI： 10.1007/s10228-009-0142-x

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The cichlid fish, Astatotilapia burtoni, can acclimate and reproduce in both the K(+)-, Na(+)-, and Ca(2+)-rich waters of Lake Tanganyika (pH 8.9-9.2) and the surrounding rivers where K(+), Na(+), and Ca(2+) concentrations are low (pH 6.5). In this study, we compared sperm motility features among A. burtoni inhabiting the lake, those living in the surrounding rivers, and those from rivers that acclimates to lake water. Sperm of all three groups required extracellular Ca(2+) ([Ca(2+)]o) for sperm motility activation. However, involvement of K(+) and Na(+) were different. In sperm motility initiation of lake population, the decrease in Na(+) and increase in K(+) concentrations corresponding to a decrease in [Na(+)]o/[K(+)]o was required. In contrast, sperm motility in both the river population and those acclimated to lake water were activated only by a decrease in [Na(+)]o, suggesting that motility initiation cues regarding Na(+) and K(+) are different among populations within same species. One probable reason why the difference of initiation cues is that the concentration of K(+) in the river water (40 mM) is lower than that in the lake water (110 mM). These results suggest that sperm flagellar activation cascades of river and lake populations within this species differ as a result of adaptations to different ionic environments. J. Exp. Zool. 313A: 169-177, 2010. (C) 2010 Wiley-Liss, Inc.

DOI： 10.1002/jez.587

PubMed

Publishing type：Research paper (scientific journal)  

The reproductive behaviour of the Japanese ornate dragonet (Callionymus ornatipinnis) was studied at the northernmost limit of its distribution at Usujiri in southern Hokkaido, Japan. Field observations confirmed that C. ornatipinnis reproduced at Usujiri, and this is the first detailed description of the reproductive behaviour of C. ornatipinnis. Males were observed to swim continuously in a sandy area where females were abundant, persistently approaching females and performing courtship displays. Courtship behaviour consisted of males spreading their fins in front of females. If a female accepted a male for spawning, the pair would then ascend upward 0.7-1.2 m from the sandy bottom and release their pelagic eggs. Spawning, which occurred daily at dusk for approximately 1 h and ceased when it became dark, was related to water temperature and was only observed when water temperature exceeded 19°C. The breeding season of this species at Usujiri spanned only the month of September, which is considerably shorter than that of other dragonet species inhabiting temperate waters. The short breeding season was probably attributed to the fact that the water temperature at Usujiri only exceeds 19°C in the month of September. © The Ichthyological Society of Japan 2009.

DOI： 10.1007/s10228-009-0116-z

Publishing type：Research paper (scientific journal)  

Stress hormone response to 3 h- or 24 h-exposure to different levels of suspended solids (50-500 mg/<I>l</I> of kaolin) was evaluated in ayu <I>Plecoglossus altivelis</I>. Significant increases in serum cortisol concentrations compared to control fish in clear water were detected in fish exposed for 3 h to water with 200 and 500 mg/<I>l</I> of kaolin but not in fish after 3 h exposure to 100 mg/<I>l</I> of kaolin. Additionally, 24 h-exposure to water with 50 mg/<I>l</I> of kaolin also elevated cortisol levels of ayu. The results suggest that long-time exposure to even low levels of suspended solids can stress ayu.

DOI： 10.11233/aquaculturesci.58.425

CiNii Article

Publishing type：Research paper (international conference proceedings)  

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

Theories suggest that, in cooperatively breeding species, female control over paternity and reproductive output may affect male reproductive skew and group stability. Female paternity control may come about through cryptic female choice or female reproductive behaviour, but experimental studies are scarce. Here, we show a new form of female paternity control in a cooperatively polyandrous cichlid fish (Julidochromis transcriptus), in which females prefer wedge-shaped nesting sites. Wedge-shaped sites allowed females to manipulate the siring success of the group member males by spawning the clutch at the spot where the large males were just able to enter and fertilize the outer part of the clutch. Small males fertilized the inner part of the clutch, protected from the large aggressive males, leading to low male reproductive skew. Small males provided more brood care than large males. Multiple paternity induced both males to provide brood care and reduced female brood care accordingly. This is, to our knowledge, the first documented case in a species with external fertilization showing female mating behaviour leading to multiple male paternity and increased male brood care as a result.

DOI： 10.1098/rspb.2009.1175

PubMed

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

The distribution of aquatic animals is limited by water temperature. However, little is known about migration patterns, overwintering, and reproduction at the extremities of their distribution. To investigate the sexual maturation of Japanese pygmy squid (Idiosepius paradoxus) and their ability to survive during winter at the northern limits of their distribution, we collected samples monthly at Usujiri in northern Japan and carried out experiments on low-temperature tolerance. Squid were collected during 4 months in autumn and early winter. In autumn, all squid were large and sexually mature, and many egg masses were found on the surface of seagrass, whereas in early winter, only small immature squid were collected. A warm north-flowing current reached the Usujiri area during autumn, so the squid were likely transported by the current and some of the small squid were recruits that hatched there. Field data and the results of experiments on tolerance of the species to low temperatures showed that it cannot survive at the low temperatures around Usujiri in winter. The migration pattern of I. paradoxus may differ from the traditional pattern for marine resources, where young fish are transported passively and do not reproduce at the extremities of their distribution.

DOI： 10.1093/icesjms/fsp145

Authorship：Last author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

In two coexisting species with similar body colours, one species may acquire benefits from mimicking the body colour of the other species. In Lake Tanganyika, the zoobenthivorous cichlid Neolamprologus mustax preferentially exploits the territories of the algivorous cichlid Variabilichromis moorii as a feeding ground, even though other zoobenthivorous cichlid species are expelled from these territories. The yellow body colour of the guest species, N. mustax, resembles that of juveniles of the host species, V. moorii, adults of which have entirely black bodies. To estimate the effect of juvenile colour on aggression from conspecific adults, the responses of adult V. moorii to dummy fish of four colours (black, yellow, white, and blue) were observed in this lake system. Our observations clearly demonstrated that adult V. moorii were less aggressive toward yellow, white, and blue dummies compared to black ones, with a slight difference in response to the yellow and white or blue dummies. This study indicates that resembling the colour of host juveniles can facilitate access of the guest species to host territory, but does not provide sufficient evidence for a hypothesis that the guest species mimics the body colour of the host juvenile.

DOI： 10.1163/156853909X446181

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

1. Communities of different species are often structured according to niche differentiation associated with competitive interactions. We show that similar principles may apply on an ecological time-scale when individuals of a species having a wide size variation compete for resources, using the Lake Tanganyika cichlid Lobochilotes labiatus (5–30 cm). This species has a mouth especially adapted to suck up invertebrates from rock crevices.
2. Individualsdefendedfeedingterritoriesagainstsimilar-sizedconspecifics,butnotagainstdifferent- sized ones. Thus, territories of similar-sized fish rarely overlapped, but up to a total of seven individuals (of seven size-ranks) had broadly overlapping territories with dissimilar-sized individuals. Comparison with expectation from the null model demonstrated clearly that observed size ratios between adjacent size rank were determined non-randomly regardless of sexual combinations.
3. Larger individuals took larger prey types of larger average size, but more importantly used wider rock crevices from which to suck food than smaller individuals. We calculated pairwise values of Schoener’s index of diet overlap Cd and the values of Levin’s index of diet breadth Bd (prey type and prey size) and the same for the width of the rock crevices used for foraging (Cr and Br). Cd remained high among all combinations of the seven ranks. In contrast, Cr declined strongly in combinations of adjacent ranks (to 0·27), and was low or zero among further different size ranks. This shows that fish with overlapping territories divided the food resources largely through foraging site partitioning. Accordingly, Bd did not depend on the size difference to the nearest two coinhabiting fish, whereas Br did.
4. We conclude that this L. labiatus community is structured non-randomly: body size-dependent effects on foraging site usage result in competition with, and territorial exclusion of, similar-sized individuals, but not of dissimilar-sized individuals that were accepted as coinhabitants. Accordingly, mean body size ratios (large/small) between two adjacent ranks were consistently approximately 1·28 [standard deviation (SD) = 0·07, n = 104], while approximately 1·34 from the null model (SD = 0·34, n = 10 400 simulations). We discuss our results as an example of Hutchinson’s rule, applied originally to size ratios of different species.

DOI： 10.1111/j.1365-2656.2008.01414.x

PubMed

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Theoretical models predict that in external fertilisers, sperm competition risk selects for larger testes and larger sperm with higher velocity, at the expense of sperm longevity. Although several empirical studies have tested this prediction within a fish species, there has been little evidence that an individual male can adjust his testis size and sperm traits according to the risk of sperm competition. Using the cooperatively breeding cichlid Julidochromis transcriptus, we examined testis size and sperm traits (sperm size, velocity and longevity) of males that were assigned to monogamous pairs (without risk of sperm competition) or cooperatively polyandrous trios composed of two males and one female (with risk); the groups were reared for breeding for 2 or more months. Our experiments showed that the polyandrous males, both siring eggs in a clutch, had larger relative testis mass than the monogamous males. However, sperm traits were unrelated to sperm competition. These results suggest that individual males of J. transcriptus can adjust their testis size but not sperm traits in response to sperm competition risk. We also examined the effect of testis investment on growth rate and the somatic condition of males. Increased investment in testes slowed growth rates, whereas testis investment did not affect somatic condition, indicating a trade-off between investment in testes and growth. We conclude that testis investment, in response to perceived sperm competition risks, occurs at the expense of growth and may be a conditional reproductive strategy that is determined by the social status (monogamous or polyandrous) of each J. transcriptus male.

DOI： 10.1007/s00265-008-0598-0

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Julidochromis species, biparental substrate- brooding cichlids in Lake Tanganyika, exhibit a variety of mating systems, including monogamy, polygyny and polyan- dry. A wide range of body size in both sexes is suggested to be one of the main factors inducing this variation. We stud- ied the effect of body size on the formation of mating sys- tem in J. transcriptus in experimental aquaria with an equal sex ratio (three males, three females). In mating trials of six similar-sized fish, monogamous pairs were predominantly formed. In trials with one large male and five similar-sized fish, the large males monopolized two or three females and polygynous harems were formed. In trials with one large female and five similar-sized fish, two of five large females mated polyandrously with two males. These results suggest that body size is likely to affect the formation of mating system in this fish. We also examined parental roles of the mated fish. In monogamous pairs, both parents shared their parental tasks. In contrast, polygynous males and polyan- drous females showed less parental care. These results indi- cate that harem owners may reduce the amount of care regardless of sex. Although the benefit of polyandrous mat- ing remains unclear, harem males fertilized more eggs than monogamous males, indicating that polygyny may be a bet- ter option for male mating tactics.

DOI： 10.1007/s10164-005-0171-5

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Cooperatively breeding animals, in which helpers may participate in reproduction with dominant breeders, are ideal species for examining intraspecific variation in testis size because they often exhibit both monogamous breeding (low risk of sperm competition) and polyandrous breeding (high risk) within a population. However, little is known about testis investment as a result of sperm competition in these animals. The substrate-brooding cichlid fish Julidochromis ornatus has a cooperatively breeding system, in which some males mate monogamously and other males reproduce as dominant breeders or helpers within cooperatively breeding groups, in which male helpers frequently sire young. We examined the relationship between testis investment and male social status in relation to the risk of sperm competition. As predicted from sperm competition models, in groups with male helpers, both the male breeders and the male helpers invested more in testes mass, compared to breeding males without male helpers. We also found a positive relationship between the testes mass of male breeders and their male helpers, suggesting that males increase their investment in reproductive capability under the risk of sperm competition. Sperm competition models also predict that larger testes are associated with increased siring success. Our paternity analysis supported this prediction; we found a positive relationship between testis investment by male helpers and the number of offspring they sired.

DOI： 10.1093/beheco/arj043

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

It is suggested that some fish of the genus Juli- dochromis, substrate-brooding Tanganyikan cichlids with biparental care, breed cooperatively with helpers. We stud- ied the social system of J. ornatus in the wild and analysed genetic parentage using microsatellites. Within the stud- ied population three patterns of social system were identi- fied: monogamous pairs (61%, 44 of 72 groups), pairs with helpers (29%, 21), and polygamous harems with helpers (controlled by either a large female or large male owner; 10%, 7). In cooperatively breeding groups, the number of helpers at each nest ranged from 1 to 6 (median 1), and male helpers were more numerous than female helpers. In both sexes, the body size was different among individuals of different social status (harem owner > breeder > helper). Helpers and harem owners of both sexes exhibited brood defence although its frequency was low. The molecular analysis revealed that (1) the helpers were mostly unre- lated to dominant breeders, (2) many helpers of both sexes contributed genetically to the next generations, (3) male helpers had high siring success (41% of young in total), and (4) large young unrelated to group members were detected at 30% of observed nests, which may be due to breeder (or helper) replacements and immigration of young. We dis- cuss the implications of these results for understanding the complex social system of this species, especially the low reproductive skew in comparison with other cooperatively breeding cichlids.

DOI： 10.1007/s00265-005-0934-6

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Parental roles and the amount of care in bi-parental fish have been assumed to be determined by sex. We studied the parental behaviour in a substrate brooding cichlid Julidochromis ornatus (40-90 mm in total length) in which both parents participate in care of eggs and young. In the study population, ca 80% of paired females were larger than their partners and pairs mated assortatively for size. Males spent more time with their offspring in female-largest pairs, whereas the opposite was found for male-largest pairs. These differences in the amount of care were more conspicuous when differences in body size were greater, whereas similar sized pairs shared parental tasks. These results suggest that the amount of parental care is largely affected by the relative size within pairs independent of sex in J. ornatus. However, the frequencies of defensive behaviours were not different in both female-largest and male-largest pairs. This indicates that parental roles would not completely change as the change of the body size difference within pairs. The larger parents were socially dominant over the partners regardless of sex, and observations of aggressive behaviours within pairs suggest that the larger fish are likely to make the partners perform parental care. Higher frequencies of aggressive encounters were observed in the similar-sized pairs than in the different-sized ones. Higher costs associated with frequent aggressive behaviours in the similar-sized pairs may be related to their small brood size, and may be partly responsible for the size-assortative mating with sexual size difference in this fish.

DOI： 10.1163/1568539042664623

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Like many other gobies, males of the Isaza goby, Gymnogobius isaza endemic to Lake Biwa, Japan, conduct parental care of eggs at nests, and females are likely to choose mates while visiting nests. The reproductive strategy should induce polygyny, but Isaza males never accept additional females in one breeding cycle. Sampling data of broods indicated that the egg mass areas were much smaller than the nest sizes, suggesting that nest size is not the limiting factor in obtaining further eggs from additional females. The brood size greatly decreased as the duration of care progressed. Few individuals including caring males ate eggs, and heterospecific egg predators were rarely observed. Sixty percent of egg masses at the middle stages of egg development were infected with aquatic fungi, some being covered with a fungus mat that drastically reduced survivorship. Infected egg masses contained more eggs than non-infected ones at the same stage, indicating that large egg masses are prone to be frequently destroyed by fungi. It is likely that the activity of parental males is lowered during the long care periods at low water temperature in early spring. Such lowered activity of caring males might be responsible for infections in large broods that would have needed more care. We propose the hypothesis that male rejection of additional females may be related to optimal brood size, which will be less susceptible to fungus infection and produce more hatching young than otherwise. This hypothesis will explain not only male avoidance of additional females but also some unique reproductive behaviors of this fish such as some females' spawning of a portion of of the mature eggs in one nest.

DOI： 10.1007/s10164-004-0116-4

Publishing type：Research paper (bulletin of university, research institution)   Kind of work：Joint Work   International / domestic magazine：Domestic journal  

It was done that isolation and cross-species amplification of mictosatellite loci for parentage analysis of the Tanganyikan cichlids. The sequences of the primers and the results of cross-species amplification were reported.

CiNii Article

Publishing type：Article, review, commentary, editorial, etc. (other)   Kind of work：Single Work  

Publishing type：Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)   Kind of work：Single Work  

Presentation type：Oral presentation (general)  

Venue：長崎大学  

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Venue：長崎大学  

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Venue：長崎大学  

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Venue：長崎大学  

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Venue：長崎大学  

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Venue：Auckland, New Zealand  

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Venue：京都大学吉田キャンパス  

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Venue：京都大学吉田キャンパス  

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Venue：京都大学吉田キャンパス  

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Venue：京都大学吉田キャンパス  

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Venue：京都大学吉田キャンパス  

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Venue：大阪公立大学杉本キャンパス  

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Venue：Jeju, Korea  

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Venue：福岡クローバープラザ  

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Venue：大阪公立大学杉本キャンパス  

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Venue：大阪公立大学杉本キャンパス  

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Venue：大阪公立大学杉本キャンパス  

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Venue：大阪公立大学杉本キャンパス  

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Venue：大阪公立大学杉本キャンパス  

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In Japanese streams fishermen often give children the opportunity to enjoy natural environments by allowing them to participate in such activities as releasing fish stock and creating spawning sites, as well as by conducting habitat preservation activities, fishing schools and nature observation tours. This study assessed the educational significance of fishermen's activities involving schoolchildren using a questionnaire survey of men and women at least 20 years old who were attending an exhibition at the Nikko Laboratory of the National Research Institute of Fisheries Science in August 2010. More than 70% of the respondents acknowledged the educational significance in the people–nature relationship and mental/psychological aspects of such activities; women evaluated the significance of such activities more positively compared with men. In the social life aspect, less than 50% of the respondents acknowledged being motivated to engage in freshwater fisheries activities and to settle in the local community. Meanwhile over 70% thought the activities would improve the appreciation of freshwater fisheries and the local community and inform the value of labor and cooperation. The results suggest most people appreciate the contribution of these fishermen's activities in the education of children.

DOI： 10.3739/rikusui.74.165

CiNii Article

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Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

近年，メスによる子の父性操作が，昆虫や鳥類などの体内受精を行う動物で報告されている．体外受精を行う魚類では，２オスと１メスが共同繁殖を行うカワスズメ科魚類において，メスによる子の父性操作の可能性が示唆されている．しかし，その詳細は全く分かっていない．本研究では，共同繁殖を行う基質産卵型のカワスズメ科魚類<i>Julidochromis transcriptus</i>を用いて，水槽実験により，メスによる子の父性操作を検証することを試みた．野外観察から，この魚はクサビ形の巣で繁殖し，協同的一妻多夫の小オスは巣幅の狭い奥で，大オスは巣幅の広い入り口付近で放精するようである．このことから，メスは産卵する位置，つまり産卵位置の巣幅を変化させることで，メスが父性操作をしている可能性が考えられる．そこで，まずクサビ形の巣を作成し，大オス・小オス・メス（トリオ）で飼育・繁殖させて，産卵位置とそれぞれのオスの受精割合について検討したところ，巣幅の狭い位置で産卵した場合は，小オスの受精させた子どもの数が多かった．これにより，メスは産卵位置を選ぶことで父性操作が可能であると考えられる．さらに，産卵位置の巣幅が狭い場合に，小オスの保護行動の頻度が増加したことから，メスは小オスに受精させることで，小オスから保護の手伝いをより多く受けていることが示唆された．また，ペアでも同様に飼育・繁殖させると，ペア飼育で得られた卵塊はコンパクトに産まれているのに対し，トリオ飼育の卵塊は幅広く産まれていた．このことから，トリオのメスは2オスが受精できるように産卵位置や分布を操作しているようである．以上のことから，<i>J. transcriptus</i>のメスは受精を操作している可能性が高いと考えられる．

Presentation type：Poster presentation  

DOI： 10.14848/esj.ESJ51.0.290.0

CiNii Article

Presentation type：Oral presentation (general)  

Presentation type：Poster presentation  

琵琶湖の固有種であるハゼ科魚類イサザは，多くのハゼ科魚類と同様に，雄が石の下に造巣し，卵がふ化するまでの間保護を行う。本種の雄は１匹の雌と番うと，その雌の卵がふ化するまでの間，他雌が産卵しようとしても攻撃的に排除することが知られている。繁殖期における野外調査の結果から，産卵直後の卵群よりも，ふ化直前の卵群の方が卵数が少ないことがわかった。保護卵を食べていた保護雄はほとんどいなかったことから，保護の進行に伴う卵群サイズの低下は，雄の卵食が原因ではないと思われた。20%の巣において，水生菌に感染した卵群が見つかった。そのうちのいくつかは，マット状の水生菌に覆われていた。水生菌感染は卵発生が進んだ卵群で主に見られた。水生菌に感染した卵群における卵の生存率は著しく低かったことから，保護後期での卵群サイズの減少は，水生菌感染によるものと思われた。健康な卵群に比べて，水生菌に感染された卵群の方が卵数が多かったことは，大きな卵群ほど水生菌に感染する危険性が高いことを示唆する。以上の結果から，イサザの雄が複数雌との産卵を拒否することは，卵群サイズの増加に伴う水生菌感染の危険を避けるためであると思われた。最後に，イサザにおいて繁殖成功を最大にする最適卵群サイズが存在する可能性について考察する。

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Poster presentation  

Presentation type：Poster presentation  

Original item：2018年度日本魚類学会年会優秀発表賞（伊藤岳他、共同発表）
第66回日本生態学会ポスター優秀賞（佐伯泰河他、共同発表）

Special report：新潟大学研究推進機構朱鷺・自然再生学研究センター協力研究員

Original item：2017年度日本魚類学会年会最優秀発表賞（佐藤駿他、共同発表）
第65回日本生態学会ポスター優秀賞（伊藤岳他、共同発表）

Special report：2017年度日本魚類学会年会最優秀発表賞（佐藤他、共同発表）