Ethology最新文献

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.

The subject of brood parasitism has become the focus of widespread attention for the numerous finely tuned adaptations that have been discovered in coevolving specialist brood parasite–host systems (Davies, 2000; Krüger, 2007; Soler, 2017a). A recent study by Antonson et al. (2022) claims to have found one of these fascinating adaptations, posing the exciting conclusion that brown-headed cowbird (Molothrus ater) chicks use a niche construction strategy (alteration of its own environment for its own fitness benefit) in prothonotary warbler (Protonotaria citrea) host nests. In this experimental study, the authors have found that the selective brood reduction strategy driven by cowbird nestlings is reducing, but not eliminating host broods. According to their interpretation, this appears to represent an adaptive niche construction strategy given the brood reduction results and that survival of cowbird nestlings is higher in broods of two warbler nestlings than when alone or in broods of four warbler nestlings. This is an intriguing possibility but does a niche construction strategy allowing the survival of two nestmates really exist in brown-headed cowbirds?

Niche construction is a mechanism whereby individuals actively manipulate their environment to obtain more appropriate conditions in which their possibilities of survival and reproductive success increase (Aaby & Ramsey, 2022; Odling-Smee et al., 2013; Trappes et al., 2022). In birds, nest building is a clear example of niche construction (Trappes et al., 2022). The strategy of the common cuckoo (Cuculus canorus) nestling, which soon after hatching evicts all host nestmates from the nest, allowing it to monopolize the feeding effort of its foster parents, can be considered another clear case of niche construction. Other brood parasites (non-evictors) share the nest with host nestlings, but usually, the parasitic nestling(s) outcompetes host nestlings. This also implies an active manipulation of their environment (the nest), and therefore, this strategy could also be considered niche construction. However, Antonson et al. (2022) suggest that in the brown-headed cowbird—protonotary warbler system, the brood parasite selectively manipulates brood reduction favouring the presence of two warbler nestlings in the nest. This suggestion is based on comparisons of data on nestling warbler mortality in four experimental groups, with two parasitized and two unparasitized treatments. However, the crucial prediction of the niche construction hypothesis—that is, that the cowbird nestling causes selective host brood reduction, allowing the survival of just two host nestlings—was not demonstrated.

In addition, this study selectively cites publications and raises several other key questions. Antonson et al. (2022) base their study on the ‘beggin

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.

In long-lived monogamous species, the trigger of costly re-pairing is not always clear. Limited research suggests that within-pair behavioural compatibility may be an important driver of partnership success, as cooperation should be enhanced when pair members' decisions complement one another. Animals' decision-making processes are influenced by personality traits – defined as individual differences in behaviour that are stable in time. Despite the potential for the personality trait ‘boldness’ to (a) directly impact individual willingness to re-pair and (b) indirectly impact re-pairing choices via reproductive success, there is currently little work exploring how re-pairing decisions might be impacted by the pair members' personalities. Using a 13-year dataset, we investigated whether within-pair boldness and its relationship with breeding success explained re-pairing patterns of black-legged kittiwakes (Rissa tridactyla), breeding in two Arctic colonies. We found that pairs with dissimilar boldness levels were more likely to experience breeding failure and that failed pairs were more likely to re-pair the following year. Despite this, only one colony displayed evidence of assortative mating by boldness, and there was no indication that re-pairing impacted reproductive success the following season. Neither individual nor pair boldness directly influenced re-pairing probability; however, in both colonies, re-pairing birds chose partners that were slightly more similar to themselves in boldness than their previous mates. These results imply an indirect pathway by which poorer behavioural compatibility within pairs may lead to breeding failure and ultimately re-pairing. Our findings highlight the importance of behavioural compatibility, and possibly personality, in mitigating sexual conflict and its population-specific drivers.

Wild cheetahs Acinonyx jubatus of all age classes, from newborns to adults, use their long-distance chirps for communication with conspecifics. We investigated the ontogenetic changes of eight acoustic parameters of the chirps produced by wild-living cheetahs across 14 age classes in Kenya. Chirp maximum fundamental frequency (f0max) was found to be best acoustic correlate of cheetah age. The f0max was the highest in neonates (up to 10 kHz), then decreased steadily across age classes and reached a plateau of about 1 kHz in mature adults older than 4 years. Based on a close relationship of f0max with age, we fitted polynomial models for estimating cheetah age by their chirps. We discuss that gradual changes of chirp f0max suggest the gradual development of cheetah vocal apparatus. Model for age estimation by chirps in the cheetah proposed in this study may provide conservationists a non-invasive bioacoustic tool for estimating cheetah age, particularly at ages younger than 4 years. However, introducing more data from cheetahs of precisely known age would be necessary for obtaining more accurate results of age determination by voice for the older individuals.

Anthropogenic sources of environmental pollution are ever-increasing as urban areas expand and more chemical compounds are used in daily life. The stimulant caffeine is one of the most consumed chemical compounds worldwide, and as a result, has been detected as an environmental contaminant in all types of major water sources on all continents. Exposure of wildlife to environmental pollutants can disrupt the energy balance of these organisms, as restoration of homeostasis is prioritised. In turn, energy allocated to other key biological processes such as growth or reproduction may be affected, consequently reducing the overall fitness of an individual. Therefore, we aimed to investigate if long-term exposure to environmentally relevant concentrations of caffeine had any energetic consequences on wildlife. Specifically, we exposed wild eastern mosquitofish (Gambusia holbrooki) to one of three nominal concentrations of caffeine (0, 100 and 10,000 ng/L) and assayed individuals for metabolic rate, general activity, antipredator and foraging behaviour and body size as measures of energy expenditure or energy intake. We found no differences in any measured traits between any of the given exposure treatments, indicating that exposure to caffeine at current environmental levels may not adversely affect the energy balance and fitness of vulnerable freshwater fish.

Recognizing form and function of animal defenses is paramount to understanding the ecological and evolutionary forces behind predator and prey dynamics. Color patterns are strongly related to defensive strategies in animals. Some rely on camouflage to avoid detection, while others are brightly colored and conspicuously signal their noxiousness to potential predators. Still others combine cryptic dorsal coloration with colorful patches that are concealed in resting position but are facultatively unveiled by special behavior or simply during activity. Such hidden conspicuous color patches may be an intermediate stage in the evolution from camouflage to aposematism. Many species, especially treefrogs of the family Hylidae, are generally considered to be cryptic, yet show colorful patches on their flanks or thighs and have defensive skin secretions that may have unpalatable properties. We investigated whether the conspicuous black and yellow spotted pattern on the thighs of Eastern Gray Treefrogs (Hyla versicolor) serve as an aposematic signal. We conducted a palatability study to test whether Gray Treefrog skin secretions are unpalatable, and a clay model field study to test whether the conspicuous black and yellow thigh pattern is an aposematic warning coloration that reduces predation. Frog secretions were discriminated against during palatability assays, and clay models painted with a spotted black and yellow pattern suffered lower predation rates. Our findings support the hypothesis that hidden color patches act as aposematic signals in Gray Treefrogs and suggest that more species benefit from aposematic coloration than currently appreciated.

A defining feature of parasitism is the harm parasites cause to their host via a reduction in lifetime reproductive success. Harm, also referred to as “virulence,” may involve host mortality or sublethal effects, such as a decreased body condition or protracted development of immature individuals. We considered a system where colonies of the social spider Anelosimus eximius serve as hosts to confamilial kleptoparasitic spiders that steal food resources. In a laboratory experiment with parasitized and non-parasitized colonies, we tested whether this host–parasite interaction meets the criterium of harm to host individuals and colonies. We assessed survival and measured scaled mass indices (SMI) before and after the experimental period. Linear mixed effects models demonstrated that colonies exposed to kleptoparasites had lower SMI values at the end of the experiment compared to controls, but found no effect of kleptoparasitism on mortality in treatment and control groups. We conclude that kleptoparasites meet the criterium of harm to their host to be considered parasitic and provide the first empirical measure of virulence for this study system.

Animals evolve in complex selective regimes, where a suite of different factors can shape signal use. We might predict that more closely related species will exhibit more similar behavior than those more distantly related; however, sometimes signals are shaped more profoundly by the environment or other forces. Lizards in the genus Sceloporus communicate with conspecifics with multimodal signals that combine species-typical push-up and headbob displays and chemical signals in the form of femoral gland secretions. Here, we examine behavioral activity and signal use across three closely related populations of the Sceloporus undulatus species complex from diverse habitats across the United States, to test the relative roles of habitat and phylogeography in shaping communicative behavior. We filmed undisturbed levels of activity for free-ranging males of S. consobrinus, syn. S. u. erythrocheilus, in Colorado, S. undulatus hyacinthinus in Indiana and S. u. undulatus in Georgia, and scored frequency and rates of behavior important for communication. We found that populations differed in their use of communicative signals in a way that deviates from expectations based solely on phylogeographic proximity or habitat, suggesting that plasticity or adaptation to conditions that vary among populations may be especially important. Specifically, canonical discriminant analyses found the largest differences in movement patterns. Sceloporus u. hyacinthinus was the most behaviorally different out of the three: males in this population had lower movement rates and particularly low levels of chemosensory behavior while male S. consobrinus and S. u. undulatus showed similar rates of chemosensory acts and headbob/push-up displays. Phenotypic and environmental variation among closely related populations, in combination with phylogeographic knowledge can help us untangle the processes responsible for the origin and maintenance of organismal diversity in communicative behavior.

Among various environmental factors, temperature has been considered a main determinant of outcomes of predator–prey interactions involving ectotherms. Although numerous studies have aimed to examine temperature effects on those interactions, few studies have been conducted under fully natural conditions. In this study, we examined the degree to which temperature affects the outcomes of encounters between a Japanese pit viper (Mamushi, Gloydius blomhoffii) and its prey under natural conditions. We continuously recorded ambushing behaviors and body temperatures of these snakes in the field using videography. We found that, over the range of temperatures at which Mamushi hunted, (1) temperature has only limited effects on whether Mamushis initiate a strike at prey and whether strikes successfully hit the prey; (2) prey reactions to strikes, such as whether they dodge the strike or the latency from strike initiation to dodge, are not affected by temperature; and (3) factors such as distance to prey and prey dodging movements are greater determinants than temperature on the outcomes of encounters between free-ranging Mamushi and their prey. Our results suggest that temperature effects on the outcomes of free-ranging snake–prey interactions may be smaller than hitherto considered.