Ethology最新文献

Behavioral imprinting is a learning phenomenon by which animals acquire preferences for stimuli through perceptual exposure during critical periods, without substantial external reinforcement. Since being acknowledged in 1516 by Sir Thomas More in artificially incubated domestic chickens, imprinting has been reported in diverse species, across various sensory modalities, and during different life-history stages. Due to this diversity, imprinting research uses highly varied methodologies, with distinctive differences between the methods employed for different types of imprinting. We systematically review relevant literature, identifying and describing the range of methodologies used to study imprinting across taxa and modalities. After compiling a representative dataset of 192 behavioral imprinting-focused experiments, we categorize studies by imprinting sensory modality, focal species, ontogenetic stage addressed, and methods applied for both exposure and testing. The majority of studies in the sample focus on filial imprinting in precocial birds but nonfilial types, such as sexual or home range imprinting in altricial and non-avian species, are also present, albeit at far lower proportions. Filial imprinting is studied across different sensory modalities, mostly through applying artificial stimuli, but nonfilial imprinting studies mainly use live animals as stimuli, without isolating the relevant sensory modalities. Most studies of filial imprinting measure preference by spatial proximity, following response, or the suppression of a fear response, whereas most studies of sexual imprinting employ the attempt frequency of sexual behaviors. Finally, we analyze the relative frequencies of methodological approaches in each imprinting category, to highlight potential biases due to uneven research effort rather than intrinsic biology. The patterns and biases in imprinting methodologies that we uncover hamper attempts to establish whether different forms of imprinting share mechanistic foundations, including whether imprinting constitutes a biologically meaningful learning category.

The behavioral plasticity among and within cetacean species can be driven by their prey sources, local adaptations to environmental features, and/or interactions with human activities. One of the tactics displayed by cetaceans is the barrier feeding, in which individuals or groups herd fish schools against natural and non-natural barriers to restrict movements of their prey. Coastal odontocetes, for example, are known for using shorelines and underwater slopes to trap their prey. Here, we documented two distinct populations of Guiana dolphin using the mangrove margins as a natural barrier to herd and capture fish. The observations took place in the Cananéia estuary, São Paulo State, southeastern Brazil, and in the Paranaguá estuary, Paraná State, southern Brazil. A total of 63 dolphins over eight encounters were observed performing six different events using mangroves as a natural barrier, summing both study areas. These findings not only expand our understanding of the behavior plasticity of the species but also call attention to the importance of the mangrove ecosystem directly to Guiana dolphins and indirectly to the components of their food web.

Adolescence is a sensitive phase when cues from the social environment can shape consistent individual differences in behavioral and hormonal profiles, but the effect of the social partner on these phenotypes is not well-understood, especially for females. We therefore aimed to investigate whether the age class and sex of the housing partner affect social behavior and cortisol concentrations in female guinea pigs during adolescence and estimate the repeatability of cortisol concentrations in this life stage. Female guinea pigs were housed upon weaning for 4 weeks with either an adult female, adolescent female, or adolescent male. Social behavior was observed in the home enclosure and a preference test and social interaction test were carried out at the end of the experiment. Cortisol concentrations (baseline and response to a challenge) were measured prior to the start of the experiment and 2 and 4 weeks after pair formation. We hypothesized that the social partner would affect behavior and cortisol concentrations. We found that females housed with an adult female were less aggressive and more consistently displaced by their housing partner than females housed with an adolescent female. Sex of the housing partner did not affect focal female behavior. Regarding hormones, baseline cortisol concentration was neither significantly repeatable nor significantly affected by the housing partner. However, cortisol responsiveness was highly repeatable both 1 h and 2 h after the onset of a challenge. The age class of the housing partner affected cortisol responsiveness, with higher cortisol concentrations measured at 1 h in females housed with an adult female. These results indicate that adolescent female guinea pigs exhibit consistent individual differences in cortisol responsiveness while retaining plasticity to adjust to cues from the social environment. Taken together, we show in a female rodent that the social environment can significantly shape behavioral and endocrine parameters during adolescence.

Competition over resources often leads to intra- and interspecific interactions, which can be detrimental to the individuals involved. Thus, natural selection should favor communication systems that reliably convey information regarding the relative competitive abilities of an individual, reducing the need for physically damaging confrontation. Body size, sex, age, relatedness, and ornamentation are important factors determining dominance across diverse taxa in intraspecific interactions. These traits, when perceptible, may serve as signals across species in guilds that have frequent interspecific interactions. Hummingbirds provide a tractable system to study such community dynamics due to their high frequency of interactions, variable ornamentation, diverse body sizes, fast metabolism, and large overlap in resource utilization. Even in this system, potential interactions between morphology and coloration are rarely accounted for together when analyzing dominance between species. We take a novel approach to understanding interspecific dominance by assessing behavior, morphology, and coloration across different types of behavioral interactions. Across 11 tropical montane hummingbird species, we find that dominance is predicted by wing size and some metrics of plumage coloration. However, the biological significance of these factors varies between the different dominance behaviors performed. These results inform our understanding of interspecific signaling and its role in the evolution of intraguild communication and resource competition.

Reciprocity, one of the evolutionary explanations for cooperation, evolves between individuals when helping is conditional upon receiving help in return (“A helps B because B helped A before”). Often tested in controlled laboratory conditions, its robustness to external disturbances has rarely been evaluated. Here, we investigated whether reciprocity is robust when disturbances occur in between the donation by one individual and its return by a partner. As model system, we used a simultaneously hermaphroditic polychaete worm (Ophryotrocha diadema), where partners in isolated dyads engage in iterated exchanges of eggs for sperm (eggs are a costly donation relatively to sperm). If a partner donates eggs and the other fertilizes them, the latter is likely to donate eggs a couple of days later. (Eggs and larvae are then cared by the parents which sit at the nest and only leave it for foraging.) We removed the eggs from the nests daily or weekly and found that reciprocity decisions were not substantially altered; focal worms were more likely to lay if the partner laid before. We also found that, irrespective of treatment, worms exchanged comparable number of eggs, and were stimulated to lay significantly sooner if the partners laid a second clutch before they reciprocated. These results show that reciprocity is robust to disturbances which may happen in the 2 days’ time gap between egg donation and egg reciprocation.

Duets are one of the most complex forms of acoustic displays, involving two individuals vocalising in a coordinated way to defend resources cooperatively. However, motivation to defend resources may be sex specific and variable in time and space, which should be reflected in the changes in duet singing behaviour. We experimentally examined whether the motivation to defend resources is sex specific and seasonally variable in an Afrotropical, sedentary songbird living in pairs or small groups—the Chubb's cisticola. We broadcasted songs of males, females and duets in a random order, both at the beginning and the end of the breeding season. We quantified the birds' responses from the perspective of the entire group as well as its individual members. We found cooperative responses to each type of intruder, with the birds flying and singing. Groups consisting of two to four individuals responded significantly more strongly towards intrusions by females than pairs, and at the beginning than at the end of breeding season. Solo syllables comprised less than 4% of all recorded syllables, and in most cases were sung within a song also containing duet and chorus syllables (only 12 from 1773 songs analysed were solo songs). Males sang solo syllables more often than females (83% vs. 17% of all solo syllables) and did it significantly more often towards intruding females than males or pairs. The number of solo syllables sung by females was independent of treatment and season. Together, our results suggests that Chubb's cisticola uses duets to cooperatively defend resources located within its territory, but the intensity of reaction is sex specific and seasonally variable. We suggest that defended resources could be mates, group stability or reproductive effort. Looking at the function of duets from the perspective of the group and its particular members, various stages of the season and different resources defended by birds allow for a better understanding of cooperative singing.

The cognitive constraint hypothesis maintains reciprocity is rare among animals because it requires cognitive capabilities that are rare, if not absent, in animals. In particular, it suggests that temporal discounting, limited memory, and limited capability of complex calculations make long-term reciprocation essentially impossible for animals. The cognitive constraint hypothesis therefore predicts that, if reciprocity ever occurs in animals, it should always be immediate. In this study, we tested for long-term reciprocation in Himalayan tahr (Hemitragus jemlahicus), a species that is not notable for its advanced cognitive capabilities. We showed that tahr are able to reciprocate grooming over extended time periods, that is, that they groom preferentially those individuals from which they receive more grooming even when all cases of immediate reciprocation are excluded from analysis. These results do not support the cognitive constraint hypothesis. We note the cognitive constraint hypothesis makes two silent assumptions: that all reciprocation is necessarily calculated and that it is based on partner control processes. We suggest these assumptions are unwarranted, and that most group living animals base their ability to reciprocate on emotionally based partner choice.

Reciprocity in the form of contingent exchanges of goods and services is widespread across animals. While there is ample evidence for helping to be contingent upon the help received from a partner, less attention has been paid to partner avoidance based on harm inflicted by a partner. Here, we investigated whether partner choice for agonistic support against powerful targets is guided by loyalty received, i.e., the tendency to refrain from attacking the subject in a coalition with any third partner. We further assessed whether loyalty received by all cooperation partners may generate increased levels of betweenness in the coalition network of a group, a measure of indirect connectedness that has previously been associated with fitness benefits. Based on observational data from male coalitions against male group mates in Barbary macaques (Macaca sylvanus), loyalty received was found to predict the frequency of cooperation in coalitions and the loyalty given to a partner. We propose that loyalty-guided reciprocity will be favored in species with rank-changing coalitions where defection is particularly risky. The more loyal a male's cooperation partners were, the more central he was in the coalition network in terms of higher in betweenness, suggesting a cognitively simple strategy underlying complex network positioning. Analyses of simulated data suggest strong correlations of loyalty and betweenness to be more prevalent in the relatively small groups characteristic of many primate species.

Direct reciprocity is the tendency to repay others' cooperation. This tendency can be crucial to maintain cooperation in evolving populations. Once direct reciprocity evolves, individuals have a long-run interest to cooperate, even if it is costly in the short run. The major theoretical framework to describe reciprocal behavior is the repeated prisoner's dilemma. Over the past decades, this game has been the major workhorse to predict when reciprocal cooperation ought to evolve, and which strategies individuals are supposed to adopt. Herein, we compare these predictions with the empirical evidence from experiments with human subjects. From a theory-driven perspective, humans represent an ideal test case, because they give researchers the most flexibility to tailor the experimental design to the assumptions of a model. Overall, we find that theoretical models describe well in which situations people cooperate. However, in the important case of “indefinitely repeated games,” they have difficulties to predict which strategies people use.