Social network structure in wintering golden‐crowned sparrows is not correlated with kinship

Stable social organization in a wide variety of organisms has been linked to kinship, which can minimize conflict due to the indirect fitness benefits from cooperating with relatives. In birds, kin selection has been mostly studied in the context of reproduction or in species that are social year round. Many birds however are migratory, and the role of kinship in the winter societies of these species is virtually unexplored. In a previous study, we discovered striking social complexity and stability in a wintering population of migratory golden‐crowned sparrows (Zonotrichia atricapilla) – individuals repeatedly form close associations with the same social partners, including across multiple winters. Here, we test the possibility that kinship might be involved in these close and stable social affiliations. We examine the relationship between kinship and social structure for two of the consecutive wintering seasons from the previous study. We found no evidence that social structure was influenced by kinship. Relatedness between most pairs of individuals was at most that of first cousins (and mostly far lower). Genetic networks based on relatedness do not correspond to the social networks, and Mantel tests revealed no relationship between kinship and pairwise interaction frequency. Kinship also failed to predict social structure in more fine‐grained analyses, including analyses of each sex separately (in the event that sex‐biased migration might limit kin selection to one sex), and separate analyses for each social community. The complex winter societies of golden‐crowned sparrows appear to be based on cooperative benefits unrelated to kin selection.     

Consequences of a One-male Harem Reproductive System and Inbreeding in a Captive Group of <Emphasis Type="BoldItalic">Cercopithecus solatus</Emphasis>

In closed captive populations, where dispersal is not possible, kin recognition and behavioral avoidance are the only mechanisms by which closely related individuals can avoid inbreeding. In the absence of avoidance, a loss of genetic diversity is inevitable in successive generations.In the 1980s, the CIRMF in Gabon established a small breeding group of sun-tailed monkeys (Cercopithecus solatus) with 4 individuals, and subsequently 17 births have been registered. We aimed to describe via microsatellite genotyping the reproductive system in the colony of Cercopithecus solatus, to evaluate the loss of genetic diversity with succeeding generations, and to evaluate consequences of inbreeding depression on a measure of the lifespan reproductive success of females giving birth to inbred vs. noninbred offspring. During the 11-yr period for which data are available, only alpha males sired offspring, confirming a one-male social organization. They reproduced only during their period of tenure. Two of the 3 alpha males were responsible for all the infants born. Genetic diversity decreased and inbreeding coefficients increased with successive generations. Interbirth interval was increased following the birth of an inbred infant, indicating possible increased maternal costs of rearing inbred infants. Loss of genetic variability in this captive group of sun-tailed monkeys has led to significant inbreeding depression and demonstrates the importance of male-mediated gene flow in restricted one-male harem breeding groups.     

Cooperative investment in public goods is kin directed in communal nests of social birds

The tragedy of the commons predicts social collapse when public goods are jointly exploited by individuals attempting to maximize their fitness at the expense of other social group members. However, animal societies have evolved many times despite this vulnerability to exploitation by selfish individuals. Kin selection offers a solution to this social dilemma, but in large social groups mean relatedness is often low. Sociable weavers (Philetairus socius) live in large colonies that share the benefits of a massive communal nest, which requires individual investment for construction and maintenance. Here, we show that despite low mean kinship within colonies, relatives are spatially and socially clustered and that nest‐building males have higher local relatedness to other colony members than do non‐building males. Alternative hypotheses received little support, so we conclude that the benefits of the public good are shared with kin and that cooperative investment is, despite the large size and low relatedness of these communities, kin directed.     

Distribution of Affiliative Behavior Across Kin Classes and Their Fitness Consequences in Mandrills

Multimale–multifemale primate groups are ideal models to study the impact of kinship on the evolution of sociality. Indeed, the frequent combination of female philopatry and male reproductive skew produces social systems where both maternal and paternal kin are co‐resident. Several primates are known to bias their behavior toward both maternal and paternal kin. Moreover, allocation of affiliation toward paternal kin has been shown to depend on the availability in maternal kin: Female baboons invest more in paternal kin after the loss of preferred maternal kin. Here, we examined how affiliation co‐varies across kin classes in juvenile mandrills (Mandrillus sphinx), an Old World primate living in a multimale–multifemale society. While affiliation levels observed with the mother and with maternal half‐sibs co‐varied positively, especially in young females, we found that levels of affiliation among paternal half‐sibs correlated negatively with levels of affiliation among individuals from the same matriline (distant kin), possibly as a result of kin availability. In addition, in social species, social bonds between individuals have been linked to differentiated fitness consequences: More socially integrated individuals generally enjoy higher fitness. We therefore also tested whether affiliation during early life impacts fitness. We showed that the global amount of affiliation during juvenescence translated into possible reproductive benefits: Females who were more socially integrated gave birth on average a year before females that were less socially integrated. However, age at first reproduction was not predicted by the amount of affiliation exchanged with any particular kin class. These results add to the growing body of evidence demonstrating differential investment in bonding and possible social adjustments among different kin categories and emphasizing once more the adaptive value of sociality.     

Dominance style of female white‐faced capuchins

Dominance style, the level of tolerance displayed by dominant individuals toward subordinate ones, is exhibited along a continuum from despotic to relaxed. It is a useful concept to describe the nature of dominance relationships in macaque species and it bridges among multiple features of dominance hierarchies, aggression, kinship and conflict resolution. Capuchins share many behavioral similarities with Old World monkeys and like macaques, may exhibit a suite of covarying characteristics related to dominance. Here, we provide an assessment of dominance style by examining measures of aggression and kin bias in 22 adult female white‐faced capuchin monkeys (Cebus capucinus) in three social groups at Santa Rosa Sector, Costa Rica. We found that bidirectionality of aggression was low (mean = 6.9% ± SE 1.6). However, there were few significant correlations between kin relatedness and social behavior (approaching, grooming, proximity, and co‐feeding), even though the intensity of kin bias in grooming was moderate and higher in the larger group. We conclude that patterns of aggression and kin‐biased behavior in our study animals are dissimilar to the patterns of covariation observed in macaque species. While unidirectional aggression suggests a despotic dominance style, the moderate expression of kin bias suggests an intermediate to relaxed classification when compared with results from an analysis of 19 macaque species. Additional studies of capuchin species and behaviors associated with dominance style (i.e., conciliatory tendencies) would help to create a comparative framework for the genus Cebus, and allow for more detailed cross‐species comparison of dominance relationships across all primates. Am J Phys Anthropol 150:591–601, 2013. © 2013 Wiley Periodicals, Inc.     

Female Bechstein's Bats Share Foraging Sites with Maternal Kin but do not Forage Together with them – Results from a Long‐Term Study

In many social animals, group members exchange information about where to feed. Thereby, they may gain direct benefits, for example, if social hunting enhances individual foraging success. Alternatively, individuals may receive indirect fitness benefits by preferentially sharing information about suitable feeding sites with kin. Indeed, in some species, a positive correlation between the degree of relatedness among individuals and the overlap among their foraging areas was found. However, sharing foraging sites with kin can also have costs if it increases food competition, which is not compensated by direct benefits. The goal of this study was to investigate whether sharing of individual foraging areas in female Bechstein's bats is best explained by kin selection or by direct benefits through social foraging. To assess their individual foraging behaviour, we analysed radio‐tracking data of 22 members of one maternity colony, including nine mother–daughter pairs, seven pairs of less closely related individuals and six pairs of unrelated bats. We examined the bats' fidelity to specific foraging areas during several years and quantified the influence of kinship on the overlap among individual foraging areas. By measuring how close to each other the bats foraged, we assessed whether individuals with overlapping areas are likely to forage together. Our study confirms previous findings that Bechstein's bats show high fidelity to foraging areas across years. Moreover, we found that relatives share foraging areas significantly more often compared with unrelated colony members. Finally, our data reveal for the first time that most colony members that share foraging areas are unlikely to forage together. This suggests that female Bechstein's bats gain no direct benefits from sharing foraging areas with members of the same maternal lineage. Our findings also have implications for conservation as habitat loss within a colony's home range might expose entire matrilines to high risks.     

The Genetic Relatedness in Groups of Joint-Nesting Taiwan Yuhinas: Low Genetic Relatedness with Preferences for Male Kin

The relative importance of direct and indirect fitness and, thus, the role of kinship in the evolution of social behavior is much debated. Studying the genetic relatedness of interacting individuals is crucial to improving our understanding of these issues. Here, we used a seven-year data set to study the genetic structure of the Taiwan yuhina (Yuhina brunneciceps), a joint-nesting passerine. Ten microsatellite loci were used to investigate the pair-wised relatedness among yuhina breeding group members. We found that the average genetic relatedness between same-sex group members was very low (0.069 for male dyads and 0.016 for female dyads). There was also a low ratio of closely-related kin (r>0.25) in the cooperative breeding groups of yuhinas (21.59% and 9.68% for male and female dyads, respectively). However, the relatedness of male dyads within breeding groups was significantly higher than female dyads. Our results suggest that yuhina cooperation is maintained primarily by direct fitness benefits to individuals; however, kin selection might play a role in partner choice for male yuhinas. Our study also highlights an important, but often neglected, question: Why do animals form non-kin groups, if kin are available? We use biological market theory to propose an explanation for group formation of unrelated Taiwan yuhinas.     

Influence of kinship and spatial density on reconciliation and grooming in rhesus monkeys

Some cercopithecine primates direct disproportionate amounts of grooming, huddling, and agonistic support toward maternal kin. Disproportionate amounts of aggression are also directed toward maternal kin, however, suggesting that mechanisms that restore relationships damaged by aggression, such as reconciliation, might be biased toward these preferred social partners. Studies investigating kinship effects and reconciliation are inconsistent, however, perhaps because of differences in the environmental conditions under which behavior was observed. In order to test the effects of kinship and spatial density on affiliative and reconciliation behavior, we conducted focal and scan sampling on a group of rhesus monkeys (Macaca mulatta) living in an outdoor corral under low spatial density conditions. We then compared this data to previously published data on a group of the same species living under higher spatial density conditions. Neither overall grooming nor reconciliation were affected by spatial density once correction procedures were applied. Grooming was kin biased at both study sites, whereas reconciliation was kin biased only in the low-density group. Although data failed to support a Coping Model according to which grooming and reconciliation should go up under higher densities, we suggest that coping may be reflected not so much in overall rates of behavior but in strategic partner choices, such as the increased importance monkeys under crowded conditions appear to attach to nonkin partners. © 1996 Wiley-Liss, Inc.     

Fine‐scale genetic structure and helping decisions in a cooperatively breeding bird

In animal societies, characteristic demographic and dispersal patterns may lead to genetic structuring of populations, generating the potential for kin selection to operate. However, even in genetically structured populations, social interactions may still require kin discrimination for cooperative behaviour to be directed towards relatives. Here, we use molecular genetics and long‐term field data to investigate genetic structure in an adult population of long‐tailed tits Aegithalos caudatus, a cooperative breeder in which helping occurs within extended kin networks, and relate this to patterns of helping with respect to kinship. Spatial autocorrelation analyses reveal fine‐scale genetic structure within our population, such that related adults of either sex are spatially clustered following natal dispersal, with relatedness among nearby males higher than that among nearby females, as predicted by observations of male‐biased philopatry. This kin structure creates opportunities for failed breeders to gain indirect fitness benefits via redirected helping, but crucially, most close neighbours of failed breeders are unrelated and help is directed towards relatives more often than expected by indiscriminate helping. These findings are consistent with the effective kin discrimination mechanism known to exist in long‐tailed tits and support models identifying kin selection as the driver of cooperation.     

Relatedness,parentage, and philopatry within a Natterer’s bat (<Emphasis Type="Italic">Myotis nattereri</Emphasis>) maternity colony

Given their cryptic behaviour, it is often difficult to establish kinship within microchiropteran maternity colonies. This limits understanding of group formation within this highly social group. Following a concerted effort to comprehensively sample a Natterer’s bat (Myotis nattereri) maternity colony over two consecutive summers, we employed microsatellite DNA profiling to examine genetic relatedness among individuals. Resulting data were used to ascertain female kinship, parentage, mating strategies, and philopatry. Overall, despite evidence of female philopatry, relatedness was low both for adult females and juveniles of both sexes. The majority of individuals within the colony were found to be unrelated or distantly related. However, parentage analysis indicates the existence of a number of maternal lineages (e.g., grandmother, mother, or daughter). There was no evidence suggesting that males born within the colony are mating with females of the same colony. Thus, in this species, males appear to be the dispersive sex. In the Natterer’s bat, colony formation is likely to be based on the benefits of group living, rather than kin selection.     

Relatedness does not predict vigilance in a population of the social rodent Octodon degus

The possibility that social foragers adjust and coordinate their scanning activity when in the presence of close relatives to attain inclusive fitness benefits remains controversial and scarcely examined. To this aim, we first tested the null hypothesis of no association between foraging individuals of the diurnal rodent, Octodon degus and their pairwise relatedness (six microsatellite loci), under natural conditions. Secondly, we examined the influence of relatedness on scan effort (percent overlapping) and temporal distribution of scanning using linear regression. Finally, we evaluated whether temporal distributions of scanning were significantly lower (coordination) or higher (synchrony) than random expectations using bootstrapping. We found that pairwise relatedness between focal degus and their foraging partner did not influence the scan effort or the temporal distribution of scanning. These original, field-based findings imply that vigilance behavior in socially foraging degus is unlikely to be kin-selected and adds to results from previous lab studies in that kinship remains a poor predictor of social behavior in these animals. Overall, our study adds to others revealing that kin selection may not have had an impact on aspects of social behavior such as vigilance during social foraging.     

Does cooperation mean kinship between spatially discrete ant nests?

Eusociality is one of the most complex forms of social organization, characterized by cooperative and reproductive units termed colonies. Altruistic behavior of workers within colonies is explained by inclusive fitness, with indirect fitness benefits accrued by helping kin. Members of a social insect colony are expected to be more closely related to one another than they are to other conspecifics. In many social insects, the colony can extend to multiple socially connected but spatially separate nests (polydomy). Social connections, such as trails between nests, promote cooperation and resource exchange, and we predict that workers from socially connected nests will have higher internest relatedness than those from socially unconnected, and noncooperating, nests. We measure social connections, resource exchange, and internest genetic relatedness in the polydomous wood ant Formica lugubris to test whether (1) socially connected but spatially separate nests cooperate, and (2) high internest relatedness is the underlying driver of this cooperation. Our results show that socially connected nests exhibit movement of workers and resources, which suggests they do cooperate, whereas unconnected nests do not. However, we find no difference in internest genetic relatedness between socially connected and unconnected nest pairs, both show high kinship. Our results suggest that neighboring pairs of connected nests show a social and cooperative distinction, but no genetic distinction. We hypothesize that the loss of a social connection may initiate ecological divergence within colonies. Genetic divergence between neighboring nests may build up only later, as a consequence rather than a cause of colony separation.     

Kin recognition in social bees

Kin recognition in social insects has become a central issue in sociobiology because studies of the recognition abilities of social insects provide a test of kin selection theory. W.D. Hamilton(1) formalized kin selection theory by showing how individuals can gain fitness by increasing the reproductive output of relatives (kin). The social interactions of individuals, or groups, should be influenced by the genetic structure of the population. The ability to recognize kin can increase the adaptive value of social behavior by modulating it according to genetic relationship. From this, the specific prediction emerges: if individuals can distinguish among others with which they interact on the basis of the degree to which they are related, then behavior should be biased preferentially toward more closely related reproductive individuals.     

Absence of Within‐Colony Kin Discrimination in a Multiple‐Queen Ant,Leptothorax acervorum

Inclusive fitness theory predicts that, other things equal, individuals within social groups should direct altruistic behaviour towards their most highly related group‐mates to maximise indirect fitness benefits. In the social insects, most previous studies have shown that within‐colony kin discrimination (nepotism) is absent or weak. However, the number of studies that have investigated within‐colony kin discrimination at the level of individual behaviour remains relatively small. We tested for within‐colony kin discrimination in the facultatively multiple‐queen (polygynous) ant, Leptothorax acervorum. Specifically, we tested whether workers within polygynous colonies treated queens differently as a function of their relatedness to them. Colonies containing two egg‐laying queens were filmed to measure the rate at which individually marked workers antennated and groomed or fed each queen. Relatedness between individual queens and workers was calculated from their genotypes at four microsatellite loci. The results showed there were no differences in the rates at which workers antennated or groomed/fed their more related queen and their less related queen. Workers interacted preferentially with their potential mother queen with respect to grooming/feeding but not with respect to antennation. However, because of high queen turnover, the frequency of adult workers with their potential mother queen still present within the colony was relatively low. Overall, therefore, we found no evidence for within‐colony kin discrimination in the context of the average worker's treatment of queens in polygynous L. acervorum colonies.     

Kin Selection in Primate Groups

Altruism poses a problem for evolutionary biologists because natural selection is not expected to favor behaviors that are beneficial to recipients, but costly to actors. The theory of kin selection, first articulated by Hamilton (1964), provides a solution to the problem. Hamilton's well-known rule (br > c) provides a simple algorithm for the evolution of altruism via kin selection. Because kin recognition is a crucial requirement of kin selection, it is important to know whether and how primates can recognize their relatives. While conventional wisdom has been that primates can recognize maternal kin, but not paternal kin, this view is being challenged by new findings. The ability to recognize kin implies that kin selection may shape altruistic behavior in primate groups. I focus on two cases in which kin selection is tightly woven into the fabric of social life. For female baboons, macaques, and vervets maternal kinship is an important axis of social networks, coalitionary activity, and dominance relationships. Detailed studies of the patterning of altruistic interactions within these species illustrate the extent and limits of nepotism in their social lives. Carefully integrated analyses of behavior, demography, and genetics among red howlers provide an independent example of how kin selection shapes social organization and behavior. In red howlers, kin bonds shape the life histories and reproductive performance of both males and female. The two cases demonstrate that kin selection can be a powerful source of altruistic activity within primate groups. However, to fully assess the role of kin selection in primate groups, we need more information about the effects of kinship on the patterning of behavior across the Primates and accurate information about paternal kin relationships.     

Promiscuity drives self-referent kin recognition

Kin selection theory has been one of the most significant advances in our understanding of social behavior . However, the discovery of widespread promiscuity has challenged the evolutionary importance of kin selection because it reduces the benefit associated with helping nestmates . This challenge would be resolved if promiscuous species evolved a self-referent kin-recognition mechanism that enables individuals to differentiate kin and nonkin . Here, we take advantage of an asymmetry in the level of promiscuity among males of alternative life histories in the bluegill sunfish (Lepomis macrochirus). We show that, as a consequence of this asymmetry, offspring of "parental" males have a high level of relatedness to nestmates, whereas offspring of "cuckolder" males have a low level of relatedness to nestmates. We find that offspring of parentals do not use a direct recognition mechanism to discriminate among nestmates, whereas offspring of cuckolders use kin recognition by self-referent phenotype matching to differentiate between kin and nonkin. Furthermore, we estimate that the cost of utilizing such self-referent kin recognition is equivalent to a relatedness (R) of at least 0.06. These results provide compelling evidence for adaptive use of kin recognition by self-referent phenotype matching and confirm the importance of kinship in social behavior.     

Fluctuating populations and kin interaction in mammals

Kin selection in animals favors less aggressive interaction among related individuals. If the genetic relatedness among neighbors changes with population structure and density, behavioral interaction may also change according to the population structure. Charnov and Finerty proposed a hypothesis that kin selection in voles causes population cycles if the relatedness among neighbors decreases as density increases. Field experiments have recently tested this hypothesis. Furthermore, field studies of social interaction in voles have increased in number, so that the effects of kinship on reproductive success can be reviewed. These studies indicate that although kin interaction might be an important factor affecting social behavior and reproductive success in voles, the relationships both between kinship and degree of amicable behavior or reproductive rate, and between relatedness among neighbors and population density, are far less simple than had been supposed.     

Kinship reinforces cooperative predator inspection in a cichlid fish

Kin selection theory predicts that cooperation is facilitated between genetic relatives, as by cooperating with kin an individual might increase its inclusive fitness. Although numerous theoretical papers support Hamilton's inclusive fitness theory, experimental evidence is still underrepresented, in particular in noncooperative breeders. Cooperative predator inspection is one of the most intriguing antipredator strategies, as it implies high costs on inspectors. During an inspection event, one or more individuals leave the safety of a group and approach a potential predator to gather information about the current predation risk. We investigated the effect of genetic relatedness on cooperative predator inspection in juveniles of the cichlid fish Pelvicachromis taeniatus, a species in which juveniles live in shoals under natural conditions. We show that relatedness significantly influenced predator inspection behaviour with kin dyads being significantly more cooperative. Thus, our results indicate a higher disposition for cooperative antipredator behaviour among kin as predicted by kin selection theory.     

The Influence of Kinship on Familiar Natal Migrant Rhesus Macaques (Macaca mulatta)

In most primate species, females remain in the natal group with kin while males disperse away from kin around the time of puberty. Philopatric females bias their social behavior toward familiar maternal and paternal kin in several species, but little is known about kin bias in the dispersing sex. Male dispersal is likely to be costly because males encounter an increased risk of predation and death, which might be reduced by dispersing together with kin and/or familiar males (individuals that were born and grew up in same natal group) or into a group containing kin and/or familiar males. Here we studied the influence of kinship on familiar natal migrant rhesus macaques (Macaca mulatta) on Cayo Santiago, Puerto Rico, by combining demographic, behavioral, and genetic data. Our data suggest that kinship influences spatial proximity between recent natal immigrants and males familiar to them. Immigrants were significantly nearer to more closely related familiar males than to more distantly related individuals. Within a familiar subgroup, natal migrants were significantly closer to maternal kin, followed by paternal kin, then non-kin, and finally to males related via both the maternal and paternal line. Spatial proximity between natal immigrants and familiar males did not decrease over time in the new group, suggesting that there is no decline in associations between these individuals within the first months of immigration. Overall, our results might indicate that kinship is important for the dispersing sex, at least during natal dispersal when kin are still available.     

Co‐foundress confinement elicits kinship effects in a naturally sub‐social parasitoid

Kinship among interacting individuals is often associated with sociality and also with sex ratio effects. Parasitoids in the bethylid genus Goniozus are sub‐social, with single foundress females exhibiting post‐ovipositional maternal care via short‐term aggressive host and brood defence against conspecific females. Due to local mate competition (LMC) and broods normally being produced by a single foundress, sex ratios are female‐biased. Contests between adult females are, however, not normally fatal, and aggression is reduced when competing females are kin, raising the possibility of multi‐foundress reproduction on some hosts. Here, we screen for further life‐history effects of kinship by varying the numbers and relatedness of foundresses confined together with a host resource and also by varying the size of host. We confined groups of 1–8 Goniozus nephantidis females together with a host for 5+ days. Multi‐foundress groups were either all siblings or all nonsiblings. Our chief expectations included that competition for resources would be more intense among larger foundress groups but diminished by both larger host size and closer foundress relatedness, affecting both foundress mortality and reproductive output. From classical LMC theory, we expected that offspring group sex ratios would be less female‐biased when there were more foundresses, and from extended LMC theory, we expected that sex ratios would be more female‐biased when foundresses were close kin. We found that confinement led to the death of some females (11% overall) but only when host resources were most limiting. Mortality of foundresses was less common when foundresses were siblings. Developmental mortality among offspring was considerably higher in multi‐foundress clutches but was unaffected by foundress relatedness. Groups of sibling foundresses collectively produced similar numbers of offspring to nonsibling groups. There was little advantage for individual females to reproduce in multi‐foundress groups: single foundresses suppressed even the largest hosts presented and had the highest per capita production of adult offspring. Despite single foundress reproduction being the norm, G. nephantidis females in multi‐foundress groups appear to attune sex allocation according to both foundress number and foundress relatedness: broods produced by sibling foundresses had sex ratios similar to broods produced by single foundresses (ca. 11% males), whereas the sex ratios of broods produced by nonsibling females were approximately 20% higher and broadly increased with foundress number. We conclude that relatedness and host size may combine to reduce selection against communal reproduction on hosts and that, unlike other studied parasitoids, G. nephantidis sex ratios conform to predictions of both classical and extended LMC theories.