Journal of Ethology

Takegaki, Takeshi

doi: 10.1007/s10164-025-00879-zpmid: N/A

Lymbery, Samuel J.; Drago-Rosa, Ana; Royle, Nick J.; Duarte, Ana; Hosken, David J. ; Archer, C. Ruth

doi: 10.1007/s10164-025-00869-1pmid: N/A

Female mate choice is a major mechanism of sexual selection, influencing the evolution of behaviour, morphology and life-history. Despite being so important, much about female mate choice remains unclear. Crucially, we have a limited understanding of how mating decisions are affected by the social environment within which these decisions inevitably occur. Here, we review how the social environment influences female mate choice and discuss the wider evolutionary consequences of these effects. We examine important social environment influences on female choosiness (i.e. how much females invest in assessing potential mates), the direction of female preferences (i.e. which phenotypes females prefer) and preference strength (i.e. how strident females are in their preferences). We also consider potential coevolution between mate choice and the social environment arising because both include genes. Finally, we highlight some outstanding questions that help us more fully understand social environment impacts on female mating decisions and emphasize the need for tests of current theoretical predictions.

Lassauce, Hugo; Gossuin, Hugues; Dudgeon, Christine L.; Chateau, Olivier

doi: 10.1007/s10164-025-00866-4pmid: N/A

Reproductive behaviors in wild sharks remain largely undocumented, yet they are critical for understanding population dynamics and informing conservation strategies. The Indo-Pacific Leopard shark (Stegostoma tigrinum), listed as endangered by the IUCN, has primarily been studied in captivity, with little information on its natural mating behaviors. Here, we present the first documented observations of group copulation in free-living S. tigrinum, recorded at Abore Reef, New Caledonia. Our observations detail a sequential mating event involving two males and a single female over a 90-min period. The mating behavior followed a structured sequence, including prolonged pre-copulation positioning, male grasping of the female’s fins and tail, conspicuous siphon sac, copulatory thrusting, and clasper use consistent with previous reports from captive settings. These findings provide novel insights into the species’ reproductive strategies and highlight the importance of identifying and protecting key mating habitats. Given the conservation concerns surrounding S. tigrinum, understanding these mating mechanisms and recognizing reproductive sites are crucial for effective species management. Our study underscores the need for further field observations to better understand the reproductive ecology of S. tigrinum and support targeted conservation efforts. Digital video images related to the article are available at: http://www.momo-p.com/showdetail-e.php?movieid=momo250903st01a.

Goodmuth, Magdalena M.; Price, J. Jordan; Tobiansky, Daniel J.

doi: 10.1007/s10164-025-00861-9pmid: N/A

Learning and memory are crucial for managing complex tasks and social relationships over time in animals. While cognition in chickens (Gallus gallus domesticus) has been extensively studied, little is known about their memory capacity and its relationship with age and social rank. We tested memory retention in a flock of young (12 months) and mature (22 months) hens using a color conditioning task with delayed retention testing over increasing time intervals up to 28 days. Hens successfully recalled color-food associations even after 28 days, demonstrating a previously unreported capacity for long-term memory in this species. We found a significant interaction between age and social rank in their effects on learning speed, with higher ranking hens showing faster acquisition of the task in the older group, but no difference in learning in younger hens. Initially, younger hens performed worse than older hens, suggesting potential age-related differences in learning or memory consolidation; however, both age groups achieved perfect performance by the third testing interval. In addition, hens demonstrated behavioral flexibility by successfully transferring their learned color associations to a novel context. Our results provide new insights into the learning and memory capabilities of chickens and underscore the importance of considering flock dynamics and individual differences in studies of avian cognition.

Tanabe, Ryohei; Iwata, Yoko; Sato, Noriyosi

doi: 10.1007/s10164-025-00863-7pmid: N/A

Due to the cost of sperm production, males are expected to adjust ejaculate volume to maximize reproductive success. This study investigates how male ejaculate volume in Idiosepius paradoxus is influenced by (1) female quality (reproductive potential and mating status) and (2) the sperm stock of the male. Males are hypothesized to increase ejaculate volume when mating with females of high reproductive potential or non-virgin females with sperm-competition risk. However, no evidence supported these assumptions, suggesting the presence of other factors. We found that males consistently allocated a moderate volume of ejaculate with approximately 12% and 14 % of their sperm stock in the early and late reproductive season, respectively. This may be the most efficient way to use male reproductive resources in conditions where the male-driven mating frequency is high. It was noted that, early in the reproductive season, the ejaculate volume transferred by smaller males was similar to that transferred by larger males. This was achieved by smaller males allocating a higher proportion of their total sperm stock, despite possessing relatively fewer sperm. However, this trend was not observed in the late reproductive season. Possible explanations for the evolution of these unique patterns of ejaculate volume allocation are discussed.

Matyjasiak, Piotr; Książka, Piotr; Chacińska, Patrycja

doi: 10.1007/s10164-025-00864-6pmid: N/A

Studies investigating the effects of ambient noise on animals’ tolerance to predators and risk assessment typically rely solely on sound playbacks, neglecting multimodal perception by omitting visual or other contextual cues. To address this limitation, we tested whether the faster escape responses from an approaching potential predator observed in isolated noise playback studies—commonly attributed to heightened vigilance—actually result from the absence of typical contextual cues, such as the visible noise source (the “cross-modal sensory dissonance” hypothesis). If true, pairing noise with its typical cues should reduce or eliminate the difference in flight initiation distances (FIDs) between noise-exposed and non-noise-exposed individuals. We simultaneously exposed male barn swallows Hirundo rustica to both acoustic noise and its visual source—an agricultural tractor. Subsequently, we compared these results with those from our previous research, which utilized only tractor noise playbacks. Birds initiated flight at significantly greater distances when the noisy tractor was nearby. This effect was significantly greater than in the experiment that used only isolated noise playback. We conclude that the longer FIDs observed in barn swallows during noise-playback experiments reflect increased vigilance, rather than merely a response to the “dissonance” of hearing noise without seeing its source.

Yasuda, Chiaki I.

doi: 10.1007/s10164-025-00865-5pmid: N/A

Individual recognition can help subordinates avoid contests with lower success against familiar dominant opponents. This holds true in crustaceans, but if the dominants autotomize their weapon (chela/cheliped) before a second encounter, there is a decrease of potential fighting ability in the prior dominant and an increased chance of success in the prior subordinates than before. I examined whether familiar recognition is still effective even when subordinates encounter a familiar, but temporarily weaponless, dominant through two consecutive trials of male–male contests in the hermit crab Pagurus middendorffii. Subordinate P. middendorffii intruders avoid fights with a familiar dominant guarder. After establishing hierarchy and familiarity between subordinates and dominants possessing a weapon (major cheliped), the subordinates encountered the same dominants after experimentally induced autotomy of the weapon. Subordinate intruders actively fought with the familiar but weaponless guarders. This result might be explained by the subordinate’s updating information; that is, opponents were recognized the same but weaker than before. Information updating should be included as a new understanding of cognitive ability in invertebrates.

Kobayashi, Yuya; Hosoda, Chisaki; Kohda, Masanori; Awata, Satoshi

doi: 10.1007/s10164-025-00868-2pmid: N/A

Parental care has a direct and beneficial effect on parental fitness. An important question regarding the evolution of parental care is why parental roles and the amount of care invested are characterized by sexual bias. In species that undertake biparental care, in addition to sex-dependent factors, dominant relationships within pairs are predicted to influence parental roles, although this has rarely been assessed. In the anemonefish, Amphiprion clarkii, females are generally larger than their mates. We discovered a population in which the body-size differences within pairs varied, with males sometimes exceeding females. Using this anemonefish population, we sought to determine whether parental roles and the amount of care invested by males and females were determined by sex or body size in the breeding pairs. We found that males spent more time caring for the clutch and attacking egg predators than females, even when the size of the sexes was reversed. Furthermore, we observed that aggressive behavior was more frequently directed by females toward males, regardless of body size, and egg survival was not influenced by differences in body size. These findings provide evidence that parental roles and the amount of care provided are strongly sex-dependent in A. clarkii. Ecological factors, such as short care periods (10 d) and protandrous sex change, are considered unlikely to enhance the investment of female anemonefish in parental care.

Louca, Vasilis; Savorelli, Smilla; Vuorio, Nea; Fisher, David N.

doi: 10.1007/s10164-025-00870-8pmid: N/A

In group-living organisms, we might expect relationships between social position and other behavioural traits such as exploration, such as if certain patterns of social associations encourage exploration or if certain behavioural types both link different groups and are more likely to explore. However, directly testing these ideas is challenging as exploration can be hard to track in the field and is a difficult trait to measure in the laboratory. Furthermore, invertebrate exploration is less commonly quantified as their small size makes them hard to track. Here we quantified social networks in multiple groups of the gregarious cockroach Blaptica dubia in the laboratory and related three measures of social network position (representing overall sociability, connectedness in local cliques, and connectedness to the wider network) to measures of exploration either assayed alone or as part of an aggregation. We found none of the social network measures related to either of the measures of exploration, which were themselves not correlated. We also found that sociability and connectedness to the wider network were positively correlated, suggesting a single axis of variation in centrality within an aggregation. We found no effects of mass or sex, but there were differences between the two blocks our experiments were performed in, suggesting some effect of observer variability. Overall, our results suggest that exploration is not linked to social behaviour in this species, that cockroaches differ in the social behaviour along a syndrome integrating sociability and the tendency to move between aggregations, and that study replication should be encouraged so we can be confident identified trends are robust.

Futamura, Ryo; Morita, Kentaro; Uchida, Jiro; Okuda, Atsushi; Kanno, Yoichiro; Kishida, Osamu

doi: 10.1007/s10164-025-00871-7pmid: N/A

Since the mortality during migration is typically greater among smaller individuals, migrants should adopt growth tactics to attain a large size before their migration trip. Size-dependent growth patterns represent such a case, where smaller pre-migrants exhibit rapid growth and delay the start of migration to attain a large body size. To understand factors that shape size-dependent growth patterns, revealing the costs associated with rapid growth and delayed migration is crucial, as size-dependent growth patterns cannot be solely explained by ecological demands of growth. We focused on the trade-off between growth and survival and investigated whether faster growth rates and longer pre-migration periods incurred higher predation risk in pre-migrants of masu salmon (Oncorhynchus masou). A capture-mark-recapture survey was conducted and predation-caused wounds as a proxy for predation risk were checked. Migrants that exhibited higher growth rate did not have higher probability of predation-caused wounds, but migrants that stayed longer in the river had higher probabilities of having predation-caused wounds, especially inflicted by piscivorous birds. This implies that smaller pre-migrants extend their stay in the river to attain larger size for surviving oceanic migration, although the extended stay in the river is costly in terms of increased predation risk.