Behavioral Ecology and Sociobiology

Constraints on song type matching in a songbird Abstract In an eastern population of song sparrows (Melospiza melodia), song type matching occurs at above chance levels but does not signal aggressiveness. One explanation for the apparent ineffectiveness of matching as a signal is that the occurrence of matching is constrained by internal rules for ordering the production of song types. This constraint hypothesis is tested here in an experiment in which the singing of territorial male song sparrows is monitored in the field in real time, and subjects are confronted with playback of one of their song types either immediately after switching away from that type (short-delay) or after having cycled through much of their repertoire since last singing that type (long-delay). Matching was not significantly more likely in the long-delay treatment than in the short-delay treatment. The probability of matching did, however, depend significantly on prior bout length: the longer was a singer's last bout of a song type, the less likely the singer was to match it. There was also a suggestive effect of frequency of usage: males were more likely to match a song type the more frequently they normally sang that type, though this result was not significant after correcting for multiple comparisons. Thus, internal rules on how songs are sequenced exert constraints on the occurrence of song type matching, and such constraints can help to explain the apparent ineffectiveness of matching as a signal in this study population. Significance statement Research on song type matching in songbirds has largely focused on the signal function of matching, especially on the hypothesis that matching serves as an aggressive signal directed at the matched individual. In some songbirds, however, such as our study population of eastern song sparrows, predictions of the aggressive signaling hypothesis are not supported. Here, we show that the probability that song sparrows match song playback is strongly influenced by internal rules governing the sequencing of song type production. Specifically, the probability that song sparrows will match a particular song type is inversely related to the length of their prior bout of that song type. This result demonstrates how internal syntactical rules governing song type sequencing can constrain the signal function of song type matching.

Habituation and ecological salience: insights into the foraging ecology of the fringed-lipped bat, Trachops cirrhosus Abstract Animals are often confronted with more sensory stimuli than they can attend to, and so should pay attention to stimuli that are relevant to them and habituate to those that are not. We investigated attention in the fringe-lipped bat, Trachops cirrhosus, by playing repeated prey sounds to bats in a habituation-discrimination paradigm. We measured two behavioral responses: initial response and habituation rate, and also tested whether the bats discriminated between the different sounds. We found that bats habituated more quickly to sounds of unpalatable prey species, but contrary to our expectation, a bat's initial response was unrelated to prey palatability. Furthermore, discrimination was only detectable when bats became strongly habituated and they were less attracted to the habituated sound compared to the subsequently presented sound in the stimulus pair. Our results support the idea that in nature, many sounds can draw an animal's attention initially, but only sounds of ecological significance and perceptual salience maintain an animal's attention over time. Significance statement Habituation is an almost ubiquitous way that animals filter environmental information, but is often overlooked in behavioral experiments. Animals may habituate faster to sounds that are unlikely to affect their lives and more slowly to ones that are associated with food or threats. We studied the predatory bat Trachops cirrhosus that hunts using prey sounds. We presented bats with prey and non-prey sounds and observed their responses over time. We found that although bats responded similarly to all the sounds at their onset, they paid attention longer to sounds from palatable prey and habituated quickly to sounds from inedible animals. This species initially attends to new sounds that it hears, but habituates in a way that helps it selectively attend to important stimuli.

The redder the better? Information content of red skin coloration in female Japanese macaques Abstract Primates appear unusual among mammals in the expression of female colorful ornaments in the absence of sex role reversal. Most studies of female ornamentation in primates have focused on the sexual signaling function of female exaggerated ano-genital swellings in female-female competition and male attraction, but other female colorful ornaments, such as red skin coloration, may also contain information about reproductive status and individual characteristics. We analyzed variation in facial and hindquarter coloration (redness and luminance) according to the timing of the fertile phase (intra-cycle variation), the cycle number, whether the cycle was conceptive or non-conceptive (inter-cycle variation), and in relation to individual characteristics (social rank, parity, and body mass) in 12 captive female Japanese macaques (Macaca fuscata). While facial and hindquarter coloration did not accurately indicate the timing of the fertile phase, variation in hindquarter luminance signaled perceptible differences between pre- and post-ovulation stages. Hindquarters became less red, and faces were lighter as the number of consecutive cycles increased. Hindquarters were redder during non-conceptive cycles compared with conceptive ones. Individual variation in skin redness and luminance appeared perceptible under good light conditions. Higher-ranking females had darker hindquarters. We also found that variation in female skin coloration may contain information about differences in body mass but not in parity. Female skin coloration in Japanese macaques may thus be more indicative of inter-cycle variation and various specific female characteristics than the timing of the fertile phase. Our study provides insight into the potential information content of this signal and demonstrates the characteristics that males might be selecting for should males prefer redder females. Significance statement Primates are the most colorful group of mammals. Females of some primate species display red skin color that is suggested to play a role in mate attraction by reflecting reproductive status or individual characteristics. In Japanese macaques, a species lacking accurate behavioral and auditory indices of the probability of ovulation, female red skin coloration (face and hindquarters) may influence mating activity. Our study shows that this colorful trait does not contain information about the timing of the fertile phase and parity but may indicate inter-cycle differences and some female characteristics. Our findings add to a growing body of research on the possible roles and functions of female colorful ornaments in animal sexual communication.

Genetic consequences of social dynamics in the Andean condor: the role of sex and age Abstract Social living can be facilitated by cooperative advantages, yet also incurs in important competitive interactions, leading to complex patterns of spatial genetic structure. Vultures provide a valuable example of complex social animals, with potential conflicts between cooperative and competitive behaviors. Yet, little is known about the socio-genetic structure of this guild because of the inherent difficulties of sampling highly mobile species with large geographical ranges. Herein, we genotyped 300 non-invasive samples from Andean condor (Vultur gryphus) with microsatellite markers to investigate the social dynamics in this highly vagile vulture that possess a despotic social system and communal roosting behavior. We explored the role of age and sex in the dispersion and relatedness patterns of the Andean condor across the central region of Argentina. We provided evidence of age-biased dispersal, supporting the idea that immature condors are largely nomadic using temporary roosting sites during exploratory flights. Our results also insinuated that sex-biased dispersal is age-dependent, with male-biased dispersal during the early life stage, suggesting habitat exclusion by adult male despotic competition. Finally, our kinship analysis showed that regional clusters are composed of highly related adults, indicating the retention of intergenerational family members. Collectively, these results demonstrate that kin associations are driven by adult philopatry, and possibly maintained by fitness benefits of social cooperation for this species. Significance statement An important question in behavioral ecology is how and when does group living affect population structure and space use. We show that adult Andean condors exhibit philopatric behavior, resulting in kin structuring patterns. Family coalitions may facilitate cooperative strategies to locate and secure costly resources, resulting in indirect fitness benefits. However, immature individuals seem to be excluded from adult territories due to despotic competition or because of an innate exploratory behavior, resulting in a scattered distribution pattern. Understanding the genetic consequences of social dynamics not only increase our knowledge of the behavioral ecology of elusive wide-ranging species, but is also essential in wildlife monitoring to design effective genetic sampling.

Insect harem polygyny—the case of Cardiocondyla ants: a comment on Griffin et al. (2019)

The relative importance of body size and UV coloration in influencing male-male competition in a lacertid lizard Abstract Communication via color signals is common in natural systems. Ultraviolet (UV)-blue patches located on the outer-ventral scales of some lacertid lizards are thought to be involved in male-male competition. However, the mechanisms that maintain their honesty remain unknown. Here, we use the common wall lizard Podarcis muralis to test whether the lateral UV-blue spots are conventional signals, the honesty of which is guaranteed by receiver-dependent costs, and discuss their potential role as an amplifier of body size. We first described the morphology and reflectance properties of lateral UV-blue spots in common wall lizards and investigated how they influence male-male competition. Spot size and number, UV chroma, and conspicuousness (calculated using vision models) were significantly greater in adult males relative to adult females and adult males relative to juveniles. Total spot area (and not spot number) of adult males was positively correlated with body size. We conducted staged competition encounters between focal males and smaller or larger rivals with control or manipulated spots. Spots were enlarged in small rivals and reduced in large rivals to disrupt the phenotypic correlation between spot area and body size. Aggressiveness and dominance were positively influenced by body size in control encounters. Spot manipulations resulted in greater submission and less aggressiveness in focal males. These results contradict the predictions associated with conventional signals and amplifiers, but suggest that spots contributed to opponent evaluation during short-distance encounters between competing males. Significance statement Many animals use color to communicate. During intraspecific resource competition, some species use color signals as an assessment tool to determine if they should engage in or avoid conflicts. Studies have found that in non-mammalian vertebrates, UV coloration can be a good indicator of fighting ability or aggressiveness. We tested whether and how the UV-blue spots of common wall lizards play a role in male-male competition by studying the properties of their spots, and then used that information to design and conduct competition experiments between males involving spot manipulation. Both body size and spot manipulation influenced aggression and submission during encounters. In particular, results suggest that spot manipulation disrupted mutual assessment and thus that spots play a role in competition signaling in male common wall lizards.

Effect of sand texture on nest quality and mating success in a fish with parental care Abstract Nest quality is an important aspect of courtship and mate choice, offering females direct benefits through offspring survival and, if it reflects male genetic quality, also indirect ones. Nest characteristics may thus affect both male mating success and reproductive success. Using the sand goby, where males build nests by covering mussel shells or stones in sand, we tested the role of nest material in male nest site choice, nest construction, and female mate choice. We examined the effect of sand texture (coarse or fine, depending on grain size) in two different settings: (A) when the male was free to choose between nest sites in different sand textures and other males were absent, and (B) when the male was denied a choice of sand texture and another male was present behind a partition. In (B), we also examined the effects of sand texture on female preference. In (A), males took up nest sites equally often in coarse and fine sand, but nests built in fine sand had greater sand cover. In (B), there was no difference in nest sand cover, but a greater number of males, and in particular males that weighed less and had been assigned coarse sand, refrained from building a nest at all. This suggests that sand texture does affect nest building in sand gobies, manifesting itself directly through nest sand cover, or indirectly through failure to build a nest. Moreover, we found that females preferred to spawn in well-covered nests regardless of sand texture. Significance statement Nests offer eggs and offspring protection from predators and inclement weather, but building material may affect both the properties of the nest and the quality of the construction. Here, we presented male sand gobies with nest sites in either fine-grained or coarse-grained sand, assessed the sand cover of the nest, and allowed females to spawn. We found that grain size influenced the amount of sand cover on the nest and affected the fraction of males that refrained from building a nest. Female spawning decision depended on the amount of sand cover, but neither males nor females expressed a preference for sand texture. Our results show that nest material is an important but indirect aspect of mating success, which may influence habitat utilization in the wild.

Resting networks and personality predict attack speed in social spiders Abstract Groups of social predators capture large prey items collectively, and their social interaction patterns may impact how quickly they can respond to time-sensitive predation opportunities. We investigated whether various organizational levels of resting interactions (individual, sub-group, group), observed at different intervals leading up to a collective prey attack, impacted the predation speed of colonies of the social spider Stegodyphus dumicola. We found that in adult spiders, overall group connectivity (average degree) increased group attack speed. However, this effect was detected only immediately before the predation event; connectivity between 2 and 4 days before prey capture had little impact on the collective dynamics. Significantly, lower social proximity of the group's boldest individual to other group members (closeness centrality) immediately prior and 2 days before prey capture was associated with faster attack speeds. These results suggest that for adult spiders, the long-lasting effects of the boldest individual on the group's attack dynamics are mediated by its role in the social network, and not only by its boldness. This suggests that behavioural traits and social network relationships should be considered together when defining keystone individuals in some contexts. By contrast, for subadult spiders, while the group maximum boldness was negatively correlated with latency to attack, no significant resting network predictors of latency to attack were found. Thus, separate behavioural mechanisms might play distinctive roles in determining collective outcomes at different developmental stages, timescales, and levels of social organization. Significance statement Certain animals in a group, such as leaders, may have a more important role than other group members in determining their collective behaviour. Often, these individuals are defined by their behavioural attributes, for example, being bolder than others. We show that in social spiders both the behavioural traits of the influential individual, and its interactions with other group members, shape its role in affecting how quickly the group collectively attacks prey.

Balancing food, activity and the dangers of sunlit nights Abstract Living in northern latitudes poses challenges to the animals that live in those habitats. The harsh environment provides a short breeding season where the sunlit summer nights provide little reprieve from visibility to predators and increased risk. In this paper, we tested the activity and food choice patterns of bank voles Myodes glareolus in early spring season, categorized by 18 h of daylight and 6 h of dusk in every day cycle. We found that territorial females showed a less predictable pattern of activity than males that were most active during the hours of dusk. The voles also showed preference to forage on high carbohydrate foods at sunset, while switching over to a more protein and fat-based diet towards sunrise. This shift is suggestive of a diet that is a direct adaptation to day-long fasts. Our results suggest a sensitive mechanism between food choice and predator avoidance in a system where light summer nights increase the predation risk considerably. Significance statement Bank voles, Myodes glareolus, are considered a model organism in ecological studies and have been used for studies of population cycles, predator-prey interactions and studies of territoriality with over a century of published records. In this study, we challenge two major preconceptions about these animals using behavioral bio-assays in a controlled environment. (1) We challenge the diurnal activity patterns of these rodents currently accepted to have a bi-modal distribution in summer months and show a unimodular activity pattern. And (2) we show that these animals are not opportunistic foragers but vary their diet to compensate for the stress of an extended daytime fast further supporting a nocturnal pattern of activity even in extreme sunlit nights where night lasts under an hour.

Social flexibility and environmental unpredictability in African striped mice Abstract The resilience of an individual to environmental change depends on its ability to respond adaptively. Phenotypic flexibility, i.e., reversible phenotypic plasticity, is such an adaptive response, which has been predicted to evolve in unpredictable environments. We present data on the environmental predictability for 17 generations of socially flexible African striped mice Rhabdomys pumilio, which can switch from group living to solitary living and back to group living. Population density during the breeding season is the main predictor of social organization in striped mice, which become solitary breeding when population density is low and plural breeding when population density is high. Using time series analysis, we could not reject randomness for the variation in population density and found a 6-year cycle for food availability. However, food availability when individual females grew up did not predict the environmental conditions during which they bred in the next year, their only breeding season. Group size was predictable and most females bred plurally in communal groups. However, single breeding is the preferred tactic to avoid infanticide but for single breeding females, it was not predictable from the environment in which they grew up whether they would become single breeders in the next breeding season. Our study indicates unpredictability in the factors most important for determining the optimal breeding tactics for 322 female striped mice. In sum, striped mice exhibit social flexibility in an unpredictable environment, making it an adaptive trait. Significance statement It has long been assumed that the evolution of different forms of sociality depends on the environment. Social flexibility, i.e., the ability of individuals to switch from group living to solitary living and back to group living, has been predicted to be an adaptation to unpredictable environments. However, the extent to which unpredictability influences sociality has never been studied previously. For female African striped mice, population density is the main factor determining whether they live alone or in groups. Here, we show that females cannot predict from the population density under which they grew up the population density under which they will reproduce, making social flexibility adaptive.

Alexandros Sfakianakis
Anapafseos 5 . Agios Nikolaos
Crete.Greece.72100
2841026182

6948891480

alsfakia@gmail.com