Behavioral Ecology and Sociobiology最新文献

Abstract

Across animal systems, abiotic environmental features, including timing of seasonal events and weather patterns, affect fitness. An individual’s degree of social integration also has fitness consequences, but we lack an understanding of how abiotic features relate to patterns of individual sociality. A deeper understanding of this relationship could be developed from studying systems where these two links with fitness have already been identified. We explored the relationship between individual social behavior and seasonal timing, seasonal length, and weather patterns. We used social network analysis on a sixteen-year dataset of a wild population of hibernating yellow-bellied marmots (Marmota flaviventer). We fit a series of generalized linear mixed models and found that longer growing seasons before winter hibernation and longer winters were associated with increased individual sociality in the following spring. However, later snowmelt was associated with decreased sociality that spring. We found no relationship between individual sociality and various measures of precipitation and temperature. This suggests that seasonal timing and length may be a more important driver of sociality than weather patterns in this system, both as a lag and contemporary effect. Seasonal timing and length may mediate the opportunity or intensity of social interactions. The entwined relationships between the seasonal schedule and weather, and the seemingly contradictory role of winter length and snowmelt, suggests the timing of seasons and its relationship with sociality is complex and further exploration of environment-sociality relationships is required across taxa.

Significance statement

While the adaptive benefits of social behavior are well studied, less is known about how features of the abiotic environment drive variation in individual social behavior. Given increasing stochasticity in the timing of seasonal events and weather patterns, mapping the environment-sociality relationship will provide important insights to the drivers of sociality in the wild. This is particularly salient for species most vulnerable to climate and environmental change, such as seasonal hibernators, like yellow-bellied marmots (Marmota flaviventer). We found that features of seasonal duration were positively associated with increased sociality, whereas the timing of seasonal onset was negatively associated. This work provides empirical evidence towards an important gap in the behavioral ecology literature.

We evaluated whether the availability of male mates affected mating strategies in a predominantly socially monogamous passerine, the grass wren Cistothorus platensis. We used the natural variation in adult sex ratio (ASR) and a male removal manipulation to assess if social polygyny was more frequent when male mates were less abundant. We evaluated the potential costs that females paid when breeding with a polygynous male by assessing how males distributed parental care between nests and analysing four correlates of breeding success (clutch size, nestling body condition, number of fledglings, and nest fate). Social monogamy was predominant when males were abundant while social polygyny was more frequent when the ASR was female-biased. The removal of males was associated with a high rate of social polygyny. Social polygyny occurred when males annexed the territory of a neighbouring female or when an unpaired female settled within the territory of a mated male. We identified several potential costs of social polygyny to females. Secondary females (females that laid eggs after the primary female) produced nestlings of lower body condition during the first half of the breeding season, received less help in feeding the brood, and increased their parental contribution. We suggest that while intrasexual competition may constrain social polygyny when males are abundant, reduced female life expectancy combined with moderate costs of male desertion may facilitate social polygyny when potential male mates are not available.

Abstract

In group-living animals, males are assumed to be dominant over females when they are larger than females. Despite this, females have sometimes been proven to be dominant over some males via the winner-loser effect, which becomes stronger when the intensity of aggression in the group is higher. To test whether the winner-loser effect leads to (partial) female dominance in a species with a pronounced sexual dimorphism, we studied the hierarchy in 12 rat colonies (Rattus norvegicus) in which the rats could freely interact with their group members within a spacious area. To investigate the underlying mechanisms, we compared the empirical data to hypotheses generated by the agent-based model ‘DomWorld’. We show that females dominated on average 55% of the males, and occupied the alpha position in four colonies, in three of them they shared it with one or several males. Moreover, in line with the predictions of the computational model, females dominated a higher percentage of males when the intensity of aggression of the colony was higher. This shows that although females are only half as heavy as males, they dominate part of the males probably through the winner-loser effect. We suggest that this effect may be widespread in many other species and can be tested experimentally.

Significance statement

It is often assumed that males automatically dominate females because males are bigger and stronger than females in many species. However, the present study shows that females can dominate males due to the winner-loser effect. We used an agent-based computational model to generate specific hypotheses that we empirically tested in a large sample of rat colonies. Despite this species having a pronounced male-biased sex dimorphism, some females dominated males – with one female even occupying an unshared alpha position. Such partial female dominance was stronger in colonies with higher intensity of aggression. Here, defeated males may suffer a drastic decrease in their fighting capability and consequently give females more opportunities to surpass them in the hierarchy.

Abstract

The size of animal groups has profound effects on individual and collective behavior, particularly in social insect colonies. Larger colonies are predicted to be more complex with more specialization among members. However, the empirical support of this theoretical expectation is limited. Hygienic behavior of honey bees is a complex cooperative behavior of workers detecting, uncapping, and removing unhealthy brood. It is an important defense against brood diseases, including the ectoparasitic mite Varroa destructor. We support the prediction that hygienic behavior increases with group size using a simulation model. To also test this prediction empirically, we performed five experiments, to compare the hygienic performance of small and large honey bee groups at four different scales, roughly representing four orders of magnitude. Hygienic performance qualitatively increased across the different scales, but different methodologies limit quantitative comparisons across experiments. Within experiments, group size was also positively related to hygienic behavior. The strongest effects of group size were measured in groups that were smaller than what honey bees adopt under natural conditions. The group-size effect on hygienic performance decreased with increasing scale and at the full colony scale, group size was unrelated to hygienic assay scores. Therefore, colony size is unlikely to confound the hygienic evaluation of colonies in apicultural practice although we demonstrate clear effects of group size on hygienic behavior. Direct observations of individual behavior that were performed in two small scale experiments did not support our prediction of increased individual specialization in larger groups. Thus, our study supports the notion of performance benefits of larger groups in the context of social immunity, although the mechanisms of how group size enhances hygienic behavior remain to be investigated further.

Significance Statement

Social insects owe their ecological success partly to their efficient division of labor and behavioral specialization of colony members. Empirical support for the theoretical argument that group performance increases with group size is insufficient. Hygienic behavior is an important defense against brood pests and diseases that threaten honey bee health. Yet, it has not been investigated with respect to group size. Here, we analyze a simulation model, demonstrating theoretically that group size is predicted to increase hygienic behavior. We then provide experimental support for this prediction across a range of group sizes, though results of some experiments are equivocal and sample sizes are limited, constraining our empirical conclusions. In small groups, we find support for the theoretical idea that hygienic performance increases with group size, but our study also indicates that this effect is not very import

Many animal species respond less aggressively to calls emitted by neighbors in comparison with strangers, an asymmetry known as the “dear enemy” effect. The adaptive significance of having “dear enemies” would be to minimize defensive costs towards less-threatening individuals (like neighbors). The opposite situation, in which known neighbors become untrustworthy, representing an even greater menace than strangers, is call “nasty neighbor effect”. In addition to these neighbor-stranger discrimination abilities, some species are also capable of recognizing neighbors individually, allowing them to avoid risky encounters based on identity and past experiences, minimizing the probability of losing an encounter. In this study we tested if black-and-gold howler monkey (Alouatta caraya) males can recognize neighbors individually and investigated the nature of long-term relationships under the dear enemy/nasty neighbors hypotheses. We conducted 36 playback experiments on four dominant males in “El Cachapé” reserve, in Argentina. We exposed each male to three different treatments, consisting of roars from: 1- Neighbors from the area of home range overlap, 2- Misplaced neighbors from the opposite side to the area of home range overlap, and 3- Strangers, quantifying eight response variables during each experiment. Our results showed that dominant males recognize neighbors individually (by roaring longer in response to misplaced neighbors), clearly reacting more aggressively to neighbors who violate mutual agreements (like home range boundaries). Also, dominant males displayed a longer roar duration and closer approach to the sound source when hearing roars from strangers, supporting the hypothesis that neighbors are dear enemies in this species. Our results show that neighbor vocal recognition is key to understanding the configuration of areas of collective use and navigation decision in primates and that strangers exert the major threat to group stability in howler monkeys.

Abstract

Phenotypic variation may influence social structure if animals associate nonrandomly based on phenotypic traits. For animals that rely on cognition for survival, variation in cognitive ability may also affect social structure. Individuals with worse cognitive abilities could benefit from preferentially associating with conspecifics with better cognition, from being more gregarious, or both, allowing them access to resources. Climatic conditions influence resource availability, which may also affect the relative benefits of assortment or gregariousness, resulting in spatiotemporal variation of social patterns. Using 5 years of data, we investigated assortment by spatial cognitive ability and associations between sociality and spatial cognition in food-caching mountain chickadees, Poecile gambeli, inhabiting harsher environments at higher elevations and milder environments at lower elevations. Elevation environments differ in overwinter severity and in the harshest winter, high elevation chickadees with better spatial learning and memory abilities were less gregarious and showed lower social differentiation (or choosiness) than those with worse spatial learning and memory abilities but did not assort based on these traits. In two other seasons, including the second harshest winter, high elevation chickadees that were less cognitively flexible showed more social differentiation than those that were more cognitively flexible. In these two seasons alone, chickadees negatively assorted by spatial learning and memory performance. Chickadees from low elevations only demonstrated negative assortment in the second harshest winter. All other results were nonsignificant, suggesting that overall, individual spatial cognitive abilities or those of their associates have little influence on social preferences.

Significance statement

We showed that under certain environmental conditions, social behavior may be related to spatial cognitive abilities in mountain chickadees that rely heavily on spatial cognition for overwinter survival, but that overall, cognition does not appear to influence social behavior. In the few years that patterns were present, they fit three trends: 1) chickadees with worse spatial cognitive abilities were more gregarious; 2) chickadees with worse spatial cognitive abilities were choosier; and/or 3) chickadees had stronger associations with social partners that had spatial cognitive abilities that differed from their own and weaker associations with those of similar cognitive abilities. While it is unclear under which specific circumstances these patterns emerge, they coincided with extreme snowfall, suggesting that individuals with worse spatial cognition alter their social behavior to buffer against their relatively greater risk of starvation under extenuating circumstances.