Behavioral Ecology and Sociobiology最新文献

Variation in aspects of carotenoid-based coloration reflects physiological health in many taxa. Painted turtles (Chrysemys picta) have brightly colored limb stripes produced by carotenoids, but the function of this color and its relation to physiological function are unknown. We tested the hypothesis that variation in painted turtle forelimb stripe coloration is associated with variation in physiological health - including glucocorticoids and both innate and adaptive immune function. We assessed adult painted turtles of both sexes across a range of sizes/ages from a long-studied population. We found that body size - a strong indicator of age in this species - was associated with changes in forelimb stripe color, such that larger turtles have brighter, more colorful stripes with increased contrast from the background forelimb color. We further found that a number of physiological health measures either changed with size, or differed between sexes, yet physiology measures were not associated with stripe color. Thus, forelimb stripe coloration is not a direct honest signal of quality. Secondarily, we provide a suite of protocols for future use to understand physiological variation of reptiles in the wild. We discuss our results in the context of signaling, physiological health, aging, and sex-specific life histories.

Supplementary information: The online version contains supplementary material available at 10.1007/s00265-025-03679-0.

Abstract: Animals are generally expected to monopolize food patches whenever possible. However, cofeeding within a defendable range occurs in many species, particularly at larger food patches, but the mechanism behind that remains underexplored. In theory, it could be due to multiple, mutually non-exclusive processes. First, larger food patches may saturate multiple top-ranking individuals, enabling cofeeding even under pure contest competition. Second, cofeeding may result from social tolerance where dominant individuals provide cofeeding concessions to certain subordinates. Third, cofeeding may result from prevailing scramble competition (i.e., indirect competition through patch exploitation) caused by large numbers of individuals that prevent monopolization ("swamping"). To investigate and differentiate between these mechanisms, we applied feeding tests to free-ranging dogs in Morocco. We provided them with a large food patch plus a varying number of small food patches. Although the small food patches were virtually always monopolized by single individuals, the dogs typically cofed in large and very dense feeding groups at the large food patches. Controlling for alternative explanations using multivariate statistics, we found that access to feeding groups was independently predicted by rank and social relationship strength, suggesting that contest competition and social tolerance play a role. However, aggression rates by top-rankers decreased with increasing feeding group size, suggesting decreasing monopolizability and increasing scramble competition. Our results underscore that social tolerance may not reduce competition but shifts it from contest to scramble competition. This can be due to active levelling, licensing more individuals access to the resource, but also to loss of control caused by swamping.

Significance statement: Although animals are generally expected to fight for resources, they are sometimes observed to cofeed peacefully in large groups. Such peaceful cofeeding is typically ascribed to and taken as a measure of social tolerance, assuming that dominants overcome their impulse to monopolize and make concessions to lower-ranking group members. Alternatively, such large peaceful cofeeding groups may result from swamping where lower-ranking group members overrun dominants as a mob. In this scenario, the dominant individuals simply lose control. Fighting would be pointless and only make them lose feeding time and reduce their share while others are feeding. Studying feedings of free-ranging dogs, we show that aggression by dominants decreases with increasing feeding group size, which supports this alternative explanation and sheds new light on the emergence of cofeeding and social tolerance.

Supplementary information: The online version contains supplementary material available at 10.1007/s00265-025-03590-8.

Abstract: Competition over access to resources, such as food and mates, is one of the major costs associated with group living. Two socioecological factors believed to drive the intensity of competition are group size and sex ratio. However, empirical evidence linking these factors to physical aggression and injuries is scarce. Here, we leveraged 10 years of data from free-ranging female and male rhesus macaques to test whether group size and adult sex ratio predicted the risk of inter and intrasexual aggression, as well as injury risk. We found evidence for an optimal group size at which the risk of intragroup aggression was minimized for both sexes. Despite male-male aggression being lowest in mid-sized groups, males in smaller groups experienced higher injury risk, suggesting within-group aggression might not be the main cause of male injury. Additionally, we found that sex ratio influenced aggression, but not injury risk. Specifically, female aggression toward other females was heightened during the birth season when groups had fewer available males, suggesting either female competition for male friends or exacerbated female-female competition due to the energetic costs of lactation. Male aggression towards females was higher in female-biased groups during the birth season and in male-biased groups during the mating season, which could reflect male competition with females over feeding opportunities and male coercion of females, respectively. Together, these findings provide insights into fitness costs (i.e., injury risk) of inter and intrasexual competition in primates in relation to key aspects of social organization.

Significance statement: While theory suggests that group size and sex ratio influence competition, studies linking these factors to aggression and injury rates are limited. Using long-term data on demography, aggression, and injury from a group-living primate, we show that both males and females experience aggression less often at intermediate group sizes. However, males in smaller groups faced higher injury risks. Although sex ratio did not predict injury risk, it did influence intra- and intersexual aggression, with patterns varying by reproductive season. Overall, our findings provide insights into how competition shapes intra and intersexual dynamics in relation to aspects of social organization.

Supplementary information: The online version contains supplementary material available at 10.1007/s00265-025-03587-3.

Abstract: Aggressive territoriality can have significant benefits for resource acquisition yet is a costly behaviour. Selection should therefore favour mechanisms that allow individuals to modify their behaviour to maintain and defend their territory whilst minimising costs. One such mechanism between intraspecific territorial competitors is neighbour-stranger discrimination. The familiarity hypothesis suggests that territory holders will respond less aggressively to neighbours they recognise than to strangers they do not recognise. Conversely, in systems where neighbours pose a greater threat to territory loss than strangers, the threat-level hypothesis predicts that neighbours will elicit a greater aggressive response. We tested these opposing hypotheses in territorial farming damselfishes Stegastes diencaeus using a common bottle presentation experiment design to initiate aggressive responses by territory holders to neighbouring and non-neighbour individuals. Neighbours that were smaller in body size than the territory holder elicited the greatest aggressive response, whereas larger neighbours elicited the weakest. The aggressive response elicited by non-neighbours did not vary greatly with body size difference between the stimulus fish and territory holder. We demonstrate that aggressive response in territorial farming damselfishes is influenced by both familiarity and potential threat determined by body size. These findings add to the growing pool of evidence that an understanding of multiple factors is needed to identify the drivers of neighbour-stranger discrimination.

Significance statement: Both familiarity and body size may mediate aggressive behaviour yet are not often included in the same study. Using manipulative field experiments, we investigated the interplay between familiarity and body size in shaping patterns of aggressive behaviour in farming damselfishes. We found that territory holders were less aggressive towards neighbours than non-neighbours, but only when they were larger than themselves. Our results showing an interaction between the effects of familiarity and body size on aggressive behaviour may hint at nuances in patterns of neighbour-stranger discrimination, such as dominance relationships.

Supplementary information: The online version contains supplementary material available at 10.1007/s00265-025-03636-x.

Despite its potential role in affecting survival, habitat use and migration strategies of juvenile birds, post-fledging parental care is poorly studied, as it requires that families can be followed over large distances. Here we combine visual observations of colour-ringed chicks being fed after fledging with GPS-tracking and accelerometer-based behavioural classification of fledged chicks and their parent(s) to quantify post-fledging parental care in Eurasian spoonbills in relation to age of the chick and sex of the chick or parent. We show that the number of observed feedings and the amount of overall contact between chicks and parents, i.e. when chick and parent were < 10 m apart, strongly decreased with chick age. Chicks were observed being fed until 125 d old, always within 40 km of the natal colony. The amount of contact strongly varied among the 16 GPS-tagged chick-parent pairs, on average decreasing from 8% of contact time at 40 d old to < 2% at 90 d. The last contact occurred at chick ages of 44-136 d (median: 88 d). All contact occurred within 18 km of the natal colony except for the first outbound migratory flight of one chick-parent pair. Both mothers and fathers engaged in post-fledging care, with some evidence that mothers had slightly more contact with chicks than fathers, overall as well as while the chick was begging or foraging. In 10 out of 11 cases that both chick and parent embarked on autumn migration, they did not migrate together: post-fledging care ended on average one week before the adult's departure and four weeks before the chick's departure on autumn migration.

Supplementary information: The online version contains supplementary material available at 10.1007/s00265-025-03649-6.

The interconnecting links between individuals in an animal social network are often defined by discrete, directed behaviours, but where these are difficult to observe, a network link (edge) may instead be defined by individuals sharing a space at the same time, which can then be used to infer a social association. The method by which these associations are defined should be informed by the biological significance of edges, and therefore often vary between studies. Identifying an appropriate measure of association remains a challenge to behavioural ecologists. Here, we use automatically recorded feeder visit data from four bird systems to compare three methods to identify a social association: (1) strict time-window, (2) co-occurrence in a group, and (3) arrival-time. We tested the similarity of the resulting networks by comparing the repeatability and sensitivity of individuals' social traits (network degree, strength, betweenness). We found that networks constructed using different methods but applying similar, ecologically relevant definitions of associations based on individuals' spatio-temporal co-occurrence, showed similar characteristics. Our findings suggest that the different methods to construct animal social networks are comparable, but result in subtle differences driven by species biology and feeder design. We urge researchers to carefully evaluate the ecological context of their study systems when making methodological decisions. Specifically, researchers in ecology and evolution should carefully consider the biological relevance of an edge in animal social networks, and the implications of adopting different definitions.

Supplementary information: The online version contains supplementary material available at 10.1007/s00265-025-03559-7.

Abstract: Cooperative behaviour is widespread in animals and is likely to be the result of multiple selective pressures. A contentious hypothesis is that helping enhances the probability of obtaining a sexual partner (i.e., confers direct benefits through sexual selection). Under this hypothesis, cooperative behaviours may have evolved into a signal. Consequently, we would expect individuals to enhance cooperation when a potential mate is present, to signal their status and quality. We evaluated this possibility in the cooperatively breeding sociable weaver (Philetairus socius). We simulated the presence of different types of individuals using a playback to test whether the simulated presence of an unknown individual, possibly a potential mate, increases provisioning rate in two classes of cooperating birds : breeders and helpers. If the signal is the provisioning rate in itself we expected increased feeding rates of male helpers during the simulated presence of an unknown female. Contrary to our predictions, the simulated presence in the audience of an unknown individual did not influence the nestling provisioning rate of birds of any sex and class. From these results, we conclude that in this species the variation in provisioning rate is unlikely to be used as a signal in a sexual selection context. However, we also highlight the limitations of our methods and suggest improvements that future studies should incorporate when testing audience effects on cooperation.

Significance statement: Animals may cooperate to gain direct benefits, like attracting mates. This happens for example in humans. In species where cooperation leads to direct sexual benefits, when the appropriate audience is present, (i.e., a potential mate), helpers should enhance their cooperation. To determine whether helping to raise others' young varies according to who is watching, we used playbacks to simulate the presence of unknown individuals of opposite sex (potential mates) while helpers were feeding young. Helping, quantified here as number of times food was brought to the chicks over an hour, was not affected by the simulated audience. We concluded that in sociable weavers variation in provisioning rate is unlikely to be a signal to obtain direct sexual benefits.

Supplementary information: The online version contains supplementary material available at 10.1007/s00265-024-03548-2.

Comparing populations across replicate environments or habitat types can help us understand the role of ecology in evolutionary processes. If similar phenotypes are favored in similar environments, parallel evolution may occur. Collective behavior, including collective movement and social networks, can play a key role in the adaptation by animals to different environments. However, studies exploring the parallelism of collective behavior are limited, with research traditionally focusing on morphological traits. Here, we asked if collective behavior varies consistently across replicate populations of benthic and limnetic three-spined stickleback (Gasterosteus aculeatus). There were repeatable, population-level differences in collective behavior in a common garden experiment, with some populations forming groups that were more cohesive and with higher strength and clustering coefficients. However, these differences were not predicted by ecotype (benthic vs. limnetic). Latency to emerge and morphology did consistently differ between ecotypes, and there were no correlations between these traits and collective behavior. Together, these results suggest that collective behavior diverges, but not in a way that is associated with variation along the benthic-limnetic axis. By examining multiple traits, we show how phenotypic evolution can be occurring in parallel and non-parallel ways at the same time. This study further highlights that the classification of habitat types may only be relevant for certain traits, with collective behavior potentially changing in a more nuanced manner.

Supplementary information: The online version contains supplementary material available at 10.1007/s00265-025-03599-z.

Evolution of signal structure should be influenced by the social environment in which signals are sent and received. The "social complexity hypothesis" for communicative complexity postulates that individuals living in complex social groups require complex signals to communicate effectively. This hypothesis has been supported in many vocalizing animals. In other systems and modalities, however, relationships between sociality and signal complexity are less clear. Weakly electric knifefishes represent a novel model for investigating the relationship between signal structure and social structure. South American apteronotid knifefish continuously produce quasi-sinusoidal electric organ discharges (EODs) from their tail to communicate species, sex, and status. Fish also rapidly modulate EOD frequency to produce chirps, which coordinate agonistic and courtship interactions. Sociality and chirp structure vary extensively across apteronotids. Here, we quantified chirp complexity and variation in chirp structure across six species that vary in group size: three territorial species (Apteronotus albifrons, Parapteronotus hasemani, and 'Apteronotus' bonapartii), two gregarious species (Adontosternarchus devenanzii and Adontosternarchus balaenops), and a semi-social species (Apteronotus leptorhynchus). Chirp complexity and variation in chirp structure differed substantially across species but were unrelated to sociality. Within the Apteronotus and Adontosternarchus species pairs, one species produced complex chirps, whereas the other produced relatively simple chirps. Thus, neither phylogenetic relatedness nor social structure explained variation in chirp structure or complexity in the species we examined.

Supplementary information: The online version contains supplementary material available at 10.1007/s00265-025-03619-y.