Female chacma baboons form strong, equitable, and enduring social bonds

Analyses of the pattern of associations, social interactions, coalitions, and aggression among chacma baboons (Papio hamadryas ursinus) in the Okavango Delta of Botswana over a 16-year period indicate that adult females form close, equitable, supportive, and enduring social relationships. They show strong and stable preferences for close kin, particularly their own mothers and daughters. Females also form strong attachments to unrelated females who are close to their own age and who are likely to be paternal half-sisters. Although absolute rates of aggression among kin are as high as rates of aggression among nonkin, females are more tolerant of close relatives than they are of others with whom they have comparable amounts of contact. These findings complement previous work which indicates that the strength of social bonds enhances the fitness of females in this population and support findings about the structure and function of social bonds in other primate groups.     

Determinants and evolutionary consequences of dominance among female gelada baboons

Summary Dominance relations among free-living female gelada baboons (Theropithecus gelada) are shown to depend on the individual's aggressiveness, modified by coalitionary support from female relatives. Relatives rank adjacent to each other more of often than expected by chance.Females are more willing both to give coalitionary support and to do so on an asymmetric basis to females with whom they interact socially (usually relatives) than to those with whom they rarely interact.The number of offspring that a female has is shown to be a function of her dominance rank. This phenomenon is probably due to the fact that females harass individuals subordinate to them when the latter are in oestrus. It is suggested that the stress caused by this harassment appears to disrupt the female's reproductive physiology, thereby inducing a high rate of anovulatory cycles and amenorrhea. In consequence, subordinate females take longer to conceive than do dominants.Simulation is used to show that females who form coalitions gain a life-time reproductive advantage over those who do not because coalitions with younger females help to prevent the decline in rank that would otherwise occur in old age.It is argued that females prefer to form coalitions with caughters rather than unrelated females because the mother-daughter relationship is the only bond of sufficient strength to provide the basis for an investment which is asymmetric in the short-term and reciprocal only over the length of a life-time. Any benefits that accrue from kin selection are considered to be secondary.     

Sex differences in fitness following a group take-over among Toque macaques: testing models of social evolution

Summary A group of toque macaques took-over the home range of one of its subordinate neighboring groups and fused with it to form a larger cohesive group. In the 7 years before the take-over, the dominant group had consistently won all contests at common feeding sites, yet the fitnesses of the females of these two groups did not differ significantly (Fig. 2A). After the take-over the females of the subjugated group occupied the lowest ranks in the combined dominance hierarchy of the merged groups (Fig. 1) and thereby lost the advantages of an own home range, such as priority of access to food. Consequently, in the merged group, survivorship and reproductive success among the subjugated females were significantly less than among the females of the dominant subgroup (Table 2, 4). The dominant matrilines grew numerically and replaced all of the subjugated females, and all but one of their offspring, within 8 years after the take-over (Fig. 2B). These data support the hypothesis that cooperation among female kin in defending resources against strange females is important in the evolution of female-bonded groups. Before the merger all 5 natal males of the subordinate group had transferred to the dominant group, where they occupied high and mid-level dominance ranks (Fig. 1). These males survived at a significantly greater rate than their subordinate female kin. Thus, the cost of group transfer seems to be greater for females than for males, and this may be one reason that females generally do not emigrate or that groups do not fuse. The data suggested three hypotheses. First, since large body size and other adaptations for fighting, giving males an advantage in male-male competition for mates, are also of advantage in resource competition with males and females, such male characters may also be favored by non-sexual selection, especially where male reproductive strategy involves group transfer. Second, female bonded groups evolved as female defensive coalitions against not only female but also male resource competitors, there having been a mutual influence in the coevolution of large-sized males and female gregariousness. Third, female defensive coalitions against large-sized aggressive males are also advantageous out-side the context of food competition, or, independent of foraging strategy.     

Kinship and social tolerance among female and juvenile wild house mice: kin bias but not kin discrimination

Kin-biased social tolerance among house mice has been interpreted in terms of kin discrimination. However, several lines of evidence suggest it may instead be an incidental artifact of group member discrimination. This leads to very different predictions about the social consequences of relatedness within and between social groups. Social interactions between wild-stock adult female and juvenile house mice (Mus domesticus) established in neighbouring territorial groups within enclosures reveal relatedness to dominant males within groups as the major factor determining social tolerance of juveniles by females. Relatedness to the female herself had no significant independent effect on responses indicating tolerance. Females were generally more aggressive toward neighbouring-group juveniles (all unrelated to females) compared with those from their own group (all related to females), but were most aggressive toward neighbouring juveniles sired by the neighbouring dominant male. They were also more aggressive toward their own-group juveniles that had been sired by the neighbouring dominant but only when encountered in the neighbouring territory and with a greater bias against female juveniles. Females were least aggressive toward own-group juveniles sired by their own-group dominant male. The sire-bias in tolerance among females is similar to that reported among the dominant males themselves in an earlier study. As a result of the combined sire-bias in tolerance by adult males and females, juveniles sired by their own-group dominant males become less likely to intrude into a neighbouring territory with time. Overall, the results suggest that differences in social tolerance reflect discrimination on the basis of social group membership rather than relatedness between interactants and thus provide strong experimental evidence in support of incidental kin bias rather than kin discrimination.     

Components of lifetime reproductive success in communally and solitarily nursing house mice — a laboratory study

Under laboratory conditions, communal nursing among familiar and closely related female house mice (Mus domesticus) improved lifetime reproductive success compared to females rearing litters alone or females living with a previously unfamiliar, unrelated partner (reproductive success was measured within an experimental lifespan of 6 months, standardized as 120 days after mating at the age of about 2 months). An analysis of the contribution of three multiplicatively combined components to variation in reproductive success among breeding females revealed that, in all three social groups, survival of young until weaning contributed most to differences in lifetime reproduction (46–64% of the total variance). Females living with a sister had a significantly higher probability of reproducing successfully than females in the other groups, and also reared significantly more litters communally than females sharing nests with an unrelated partner. Weaning probabilities of young were highest in litters cared for by sisters and lowest in nests of unrelated females. Young were found dead either directly after birth (within the first 2 days of lactation) or after they had been cared for and nursed for at least 1 day. The loss of an entire litter typically occurred directly after birth. In monogamous females rearing litters alone the death of almost all young coincided with such early entire-litter mortality. In polygynous groups, however, offspring died at an older age and more litters suffered the loss of some young. Still, rearing young with a sister improved survival directly after birth and fewer litters were lost entirely in comparison with females in the other groups. In polygynous groups, pregnant females were observed to kill some of their partner's dependent young shortly before they gave birth themselves. As a consequence, individual young had reduced survival when they were firstborn in a communal nest (another litter was born within 16 days). Analyzed over a lifetime, communal care among familiar and closely related female house mice seems to be an adaptation to maximize the survival of offspring until weaning.     

Long‐Term Impacts of Poaching on Relatedness,Stress Physiology,and Reproductive Output of Adult Female African Elephants

Abstract: Widespread poaching prior to the 1989 ivory ban greatly altered the demographic structure of matrilineal African elephant (Loxodonta africana) family groups in many populations by decreasing the number of old, adult females. We assessed the long‐term impacts of poaching by investigating genetic, physiological, and reproductive correlates of a disturbed social structure resulting from heavy poaching of an African elephant population in Mikumi National Park, Tanzania, prior to 1989. We examined fecal glucocorticoid levels and reproductive output among 218 adult female elephants from 109 groups differing in size, age structure, and average genetic relatedness over 25 months from 2003 to 2005. The distribution in group size has changed little since 1989, but the number of families with tusked old matriarchs has increased by 14.2%. Females from groups that lacked an old matriarch, first‐order adult relatives, and strong social bonds had significantly higher fecal glucocorticoid values than those from groups with these features (all females R²= 0.31; females in multiadult groups R²= 0.46). Females that frequented isolated areas with historically high poaching risk had higher fecal glucocorticoid values than those in low poaching risk areas. Females with weak bonds and low group relatedness had significantly lower reproductive output (R²[U]=0.21). Females from disrupted groups, defined as having observed average group relatedness 1 SD below the expected mean for a simulated unpoached family, had significantly lower reproductive output than females from intact groups, despite many being in their reproductive prime. These results suggest that long‐term negative impacts from poaching of old, related matriarchs have persisted among adult female elephants 1.5 decades after the 1989 ivory ban was implemented.     

The reproductive consequences of male cooperation in the red howler monkey: paternity exclusion in multi-male and single-male troops using genetic markers

Summary Variance in male reproductive success in single and multi-male red howler (Alouatta seniculus) troops was examined through paternity exclusion using genetic markers. Coalitions of relatives were compared to coalitions of non-relatives with regard to duration, stability, and number of offspring expected for each participant based on paternity exclusion results. No evidence of paternity by males living outside of the troop was found. In multi-male troops, only the dominant male was found to father offspring conceived during his tenure. This was the only male observed to mount females. In both troops examined genetically wherein a status change had occurred, paternity changed with status. Coalitions of relatives and potential relatives lasted significantly longer than coalitions of non-relatives, and experienced fewer status changes between males. A direct advantage of forming a coalition for both dominant and subordinate red howler males resulted from the superior competitive ability of coalitions over single males in establishing and maintaining tenure in the limited number of female troops in the population. Although the mating success of a subordinate male in a coalition appears to be extremely low, his chances of achieving membership in a bisexual troop as a single male may be even lower. Since the majority of troops in the population during any given year were multi-male or age-graded male (85%–96%), the number of troops that a single male would be able to invade unaided was very small. A subordinate male may be able to assume dominance, particularly if he is a subadult. In coalitions in which males are related, the subordinate male will further benefit from inclusive fitness. A dominant male that forms a coalition with a relative can expect to have longer reproductive tenure than in a troop with a non-relative, thereby producing more offspring and directly enhancing his fitness. Anecdotal evidence suggests that males choose relatives over non-relatives as coalition partners when possible.     

Paternal kin bias in the agonistic interventions of adult female rhesus macaques (Macaca mulatta)

When agonistic interventions are nepotistic, individuals are expected to side more often with kin but less often against kin in comparison with non-kin. As yet, however, few mammal studies have been in a position to test the validity of this assertion with respect to paternal relatedness. We therefore used molecular genetic kinship testing to assess whether adult female rhesus macaques (Macaca mulatta) from the free-ranging colony of Cayo Santiago (Puerto Rico) bias their interventions in ongoing dyadic aggressive interactions towards maternal and paternal half-sisters compared with unrelated females. It turned out that females supported maternal half-sisters significantly more often than paternal half-sisters or non-kin regardless of the costs associated with such interventions. Similarly, females targeted maternal half-sisters significantly less often than non-kin when this was associated with high costs. Unrelated females provided significantly higher mean rates of both high- and low-cost support to each other than did paternal half-sisters. However, females targeted paternal half-sisters significantly less often than non-kin when targeting was at low cost, suggesting that females refrain from intervening against paternal half-sisters. Our data confirm the general view that coalition formation in female mammals is a function of both the level of maternal relatedness and of the costs of intervention. The patterns of coalition formation among paternal kin were found to be more complex, and may also differ across species, but clear evidence for paternal kin discrimination was observed in female rhesus as predicted by kin selection theory.     

Kin-related spatial structure in brown bears Ursus arctos

Kin-related social structure may influence reproductive success and survival and, hence, the dynamics of populations. It has been documented in many gregarious animal populations, but few solitary species. Using molecular methods and field data we tested: (1) whether kin-related spatial structure exists in the brown bear (Ursus arctos), which is a solitary carnivore, (2) whether home ranges of adult female kin overlap more than those of nonkin, and (3) whether multigenerational matrilinear assemblages, i.e., aggregated related females, are formed. Pairwise genetic relatedness between adult (5 years and older) female dyads declined significantly with geographic distance, whereas this was not the case for male–male dyads or opposite sex dyads. The amount of overlap of multiannual home ranges was positively associated with relatedness among adult females. This structure within matrilines is probably due to kin recognition. Plotting of multiannual home-range centers of adult females revealed formation of two types of matrilines, matrilinear assemblages exclusively using an area and dispersed matrilines spread over larger geographic areas. The variation in matrilinear structure might be due to differences in competitive abilities among females and habitat limitations. The influence of kin-related spatial structure on inclusive fitness needs to be clarified in solitary mammals.     

O brother,where art thou? The varying influence of older siblings in rank acquisition by female baboons

Males in sexually dimorphic species like baboons appear to have surprisingly little influence on the reproduction and dominance ranks of their female kin, even though they could potentially increase their fitness by helping their relatives improve their ranks. Male baboons are able to dominate females several years before they emigrate, but their presence has no effect on relatives’ dominance ranks, at least when female kin are present. As a result, females usually acquire ranks within their matriline, above their older sisters. We describe the process of rank acquisition among orphaned and non-orphaned juvenile and adolescent females in a group of free-ranging baboons. Orphaned females were significantly more likely than non-orphaned females to acquire unexpected ranks. Orphaned females with older sisters often acquired ranks within the matriline, but below their older sisters’. Orphaned females with older brothers were likely to rise in rank above their matriline. Females’ interventions on behalf of younger sisters always supported the existing female dominance hierarchy, while males’ interventions tended to act against it. Similarly, in playback experiments, females appeared to be willing to support their younger sister only in disputes with lower-ranking females. In contrast, males appeared to be willing to support their sister even in disputes with higher-ranking females. Fraternal support enables females to improve their dominance ranks, but only if their mothers have died. It remains a puzzle why males have so little influence on their female relatives’ ranks when female kin are present, and so much when they are absent.     

Interactions among females in polygynous yellow-headed blackbirds

Summary Two alternative hypotheses which attempt to predict how females within harems in polygynous species should behave toward one another were examined in a population of yellow-headed blackbirds (Xanthocephalus xanthocephalus). The hypothesis that females within a harem are co-operative was not supported. Females in large harems did not enjoy higher reproductive success than those in smaller harems and females within a territory did not initiate their nests close in time or space. The alternative hypothesis that females within a harem are competitive was also not supported. Nest density did not have a negative effect on female reproductive success, females within a territory did not initiate their nests far apart in time or space, and resident females were not very aggressive toward intruding female mounts during the settling period. The data support the idea that females settled independently of one another and had no effect on one another's reproductive success.     

Philopatry,reproductive success of females,and maternal investment in the red-necked wallaby

Summary Female red-necked wallabies settle within their mothers' home ranges, apparently for life, while males disperse at about two years of age. However, sons spend much more time with their mothers before dispersing than do daughters of similar ages. Females who associate regularly with their subadult offspring are less likely to reproduce successfully at their next breeding attempt than are females who spend little time with their subadults, and sons therefore impose greater short-term reproductive costs on their mothers than do daughters. Females who are generally gregarious also suffer reduced reproductive success, even though reproductive success is independent of local density. It is suggested that the reproductive costs to females of associating with their subadult offspring, and other relatives, are incurred through tolerance of ecological competition from those kin, and therefore reflect a form of prolonged maternal investment, which is initially heaviest in sons but is sustained for longer periods in daughters. Females produce equal numbers of male and female offspring, and spend equal amounts of time suckling them in infancy.     

Invading together: the benefits of coalition dispersal in a cooperative bird

Dispersal attempts can be costly and may often end in failure. Individuals should therefore only disperse when the benefits of dispersal outweigh the costs. While previous research has focussed on aspects of the individual that may affect dispersal success, social factors may also influence dispersal outcomes. One way of achieving successful dispersal could be through cooperative, or coalition dispersal. I investigated this possibility in the cooperatively breeding Arabian babbler Turdoides squamiceps. I found that coalition dispersal appears to be an effective strategy to ensure the success of dispersal attempts, with coalitions more successful than lone individuals at taking over the breeding position in a new group. Lone dispersal was more costly than coalition dispersal, with lone individuals suffering a greater loss of body mass during dispersal attempts. These results suggest a substantial short-term benefit for this type of cooperative behaviour. There was no evidence for dispersal polymorphism in the population, with no detectable phenotypic difference between dispersers and non-dispersers or those that dispersed as part of a coalition compared with those that dispersed alone.     

Genetic reconstruction of breeding patterns in gundis (Rodentia: Ctenodactylidae)

Current mating system theory predicts that the number of females breeding in a group will depend on the number of females in the group and the accessibility of unrelated males, whereas the number of males breeding in a group will depend on the ability of males to control access to reproductive females. By combining information on group composition with genetic data, I determined whether breeding patterns in a rock-dwelling rodent, Ctenodactylus gundi, were concordant with these expectations. C. gundi breeding patterns varied from facultative monogamy to uni-male polygyny to multi-male polygyny. The number of reproductive individuals of each sex in a group increased with group size. Whereas communal breeding among related females tended to increase female reproductive success, males breeding in the same group were unrelated to other group members and seemed to compete over access to matings. While some males were assigned offspring from neighboring social groups, most group-living males successfully monopolized the reproduction of females within their group. There was no evidence that females had multiply sired litters, although some bred with alternative males in separate breeding attempts. Although numerous individuals were not assigned as parents or offspring, genetic information enabled me to determine that most unassigned individuals were philopatric group members, whereas only a few were unrelated immigrants into their current social group. Together, these results provide evidence that C. gundi social groups represent fairly distinct reproductive units whose breeding patterns are dependent on group size and composition in accordance with theoretical predictions. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Family insurance: kin selection and cooperative breeding in a solitary primate (Microcebus murinus)

Lactation imposes substantial physiological costs on mothers and should therefore not be directed towards foreign offspring. Such allonursing, however, is common in mammal species that share roosts. Hypotheses to explain allonursing among such plural breeders include misdirected parental care, milk evacuation, brood parasitism, reciprocity, and kin selection. The necessary behavioral data, in combination with data on kinship and kin recognition, have rarely been available to distinguish among these explanations, however. In this study, we provide evidence for cooperative nursing and adoption by plural-breeding females in a nocturnal primate, the gray mouse lemur (Microcebus murinus), in which females forage solitarily during the night, but form day-time sleeping groups with one to two other females. We observed 34 resident females in an 8 ha study area in Kirindy Forest, Madagascar, over three consecutive annual breeding seasons and determined genetic relationships among all members of this population. Five sleeping groups of adult females were filmed inside their roosts during one breeding season after females gave birth. The composition of groups changed substantially across years, but they always consisted of close maternal relatives. All females within a group gave birth to one to three infants. They regularly transferred only their own offspring among roosting sites, demonstrating an ability to discriminate between their own and other’s offspring, but they regularly groomed and nursed related offspring other than their own and adopted related dependent young after their mother’s death. Kin selection may therefore be the main selective force behind cooperative breeding among these closely related females with a high mortality risk, providing each of them with family insurance.     

Sociality and cooperative breeding of red-cockaded woodpeckers,Picoides borealis

Summary Thirty groups of red-cockaded woodpeckers (Picoides borealis) were studied from 1976–1982 to (1) determine the demographic structure of groups, (2) identify the role helpers play in reproductive activities, and (3) investigate the selective pressures promoting sociality and helping behavior. Groups had only 1 mated pair and 0–2 helpers. Approximately half of all groups had helpers and a given group had helpers some years but not others. Helpers, with rare exception, were males 1 or 2 years old and progeny of 1 or both members of the breeding pair. As a result of higher nestling survival, groups with helpers fledged significantly more young per year than unassisted pairs ( , SD=0.97,n=43 vs. , SD=1.01,n=50). Nesting success was also associated with size and quality of nesting period home range, but evidence suggested that the increased number of young fledged resulted directly from the action of helpers. There was a significant positive correlation between reproductive success and experience of breeding females among unassisted pairs but a significant negative correlation among pairs with helpers. In groups with experienced females, helpers were assisting both their mothers and fathers and, therefore, were related to the offspring on the average by 0.50. In groups with inexperienced females, helpers were assisting their fathers and unrelated females and were related to the offspring by 0.25. The red-cockaded woodpecker's unique habit of excavating nest and roost cavities in living pines and the extended period of time required for excavation may be an important ecological constraint that promotes the retention of helpers. Because helpers are related to the offspring they help rear, kin selection and gains in indirect fitness may provide a partial explanation of why red-cockaded woodpecker helpers help. However, the negative correlation between the efficacy of helping behavior and the helpers' relatedness to the offspring they help rear implies that helpers are least effective in producing offspring which would represent greatest gains to indirect fitness. This raises questions about the relative importance of kin selection and indirect fitness in the evolution of helping behavior among red-cockaded woodpeckers.     

Fitness benefits of coalitionary aggression in male chimpanzees

Coalitionary aggression occurs when at least two individuals jointly direct aggression at one or more conspecific targets. Scientists have long argued that this common form of cooperation has positive fitness consequences. Nevertheless, despite evidence that social bond strength (which is thought to promote coalition formation) is correlated with fitness in primates, cetaceans, and ungulates, few studies have directly examined whether coalitionary aggression improves reproductive success. We tested the hypothesis that among free-ranging chimpanzees (Pan troglodytes schweinfurthii), participation in coalitionary aggression increases reproductive output. Using 14 years of genetic and behavioral data from Gombe National Park, Tanzania, we found that coalitionary aggression increased a male’s chances of (A) siring offspring, compared to other males of similar dominance rank, and (B) ascending in rank, a correlate of future reproductive output. Because male chimpanzees form coalitions with many others within a complex network, we used social network analysis to identify the types of connections correlated with these fitness benefits. The beneficiaries of coalitionary aggression were males with the highest “betweenness”—that is, those who tended to have coalition partners who themselves did not form coalitions with each other. This suggests that beyond simply recognizing third-party relationships, chimpanzees may use this knowledge to choose coalition partners. If so, this is a significant step forward in our knowledge of the adaptive value of social intelligence. Regardless of mechanism, however, this is the first evidence of genetic benefits of coalitionary aggression in this species, and therefore has important implications for understanding the evolution of cooperation.     

Kin associations and direct vs indirect fitness benefits in colonial cooperatively breeding sociable weavers Philetairus socius

Indirect fitness benefits are believed to be an important force behind the evolution of cooperative breeding. However, helpers may associate with their relatives as a result of delayed dispersal, hence, kin associations might be a consequence of demographic viscosity rather than active choice. In addition, recent studies showed that helpers may have access to reproduction therefore direct benefits might also play an important role. Here, we investigate the possible roles of direct genetic benefits and kin associations on helping behavior in the sociable weaver Philetairus socius, a colonial and cooperatively breeding passerine. We used a microsatellite-based genotyping method to describe the genetic structure within nests and colonies. Within a colony, we found considerable genetic structure between males but not females. Sociable weaver colonies have several nests that are simultaneously active, giving individuals a choice of associating with a range of first-order kin to unrelated individuals. Helpers were significantly more related to the young in the helped nests than in other nests of the colony, suggesting an active choice for associating with kin. The helpers were generally offspring or first-order relatives of one (50%) or both (43%) breeders, although more infrequently, seemingly unrelated individuals also helped (7%). We found no supporting evidence of extrapair parentage and hence no direct genetic gains from helping in our population. This strong reproductive skew is contrary to theoretical models predicting conflicts over reproduction in stepfamilies. We discuss whether female decisions and/or other direct benefits of remaining in kin associations or helping might explain the high skew observed.     

Female choice contributes to offspring fitness in the field cricket,Gryllus bimaculatus (De Geer)

Summary Females of the field cricket, Gryllus bimaculatus, are known to mate non-randomly with respect to male size. The reproductive output of females allowed to choose their mates was compared with that of females allocated mates. Females allowed to choose their mates laid a greater proportion of their available eggs, thereby investing more heavily in reproduction. Female choice did not appear to influence hatching success, suggesting that no short term benefits are derived from non-random mating. However, the offspring of females allowed to choose their mates developed more rapidly and began their own reproductive output before those of females who had been allocated mates. Furthermore, the faster developing offspring of females who chose their mates tended to have a consistantly higher survival rate as well as a lower variance in survival (i.e. less risk of mortality) at adult eclosion. Female choice may therefore contribute to offspring fitness and thus to long term reproductive success. Females allocated large males as mates did not equal those of females allowed to choose their mates, in terms of reproductive output and offspring fitness. This suggests that females may choose their mates with regard to a mixture of characters of which male size is only one.     

Pup guarding by greater spear-nosed bats

Alloparental care poses an evolutionary dilemma because effort is expended on non-filial offspring. Thus, instances of alloparental care have been attributed to either mistaken identity, (i.e., recognition errors) or active cooperation. In greater spear-nosed bats (Phyllostomus hastatus), reproductive females roost together in stable long-term social groups in cave ceilings. Non-volant pups frequently fall from roost sites to the cave floor where they can die unless retrieved by an adult. In this study, we examined the function of adult female visits to non-filial young and tested whether visits were attributable to recognition errors or to cooperation. We found that females visited non-filial pups from their own social group more than expected. Females from different social groups attacked and sometimes killed pups, and male pups were attacked more frequently than female pups. Visits by group mates benefited fallen pups by reducing the likelihood of attack by females from other groups. In contrast to the mistaken identity hypothesis, we found that some females leave their own pups to approach and remain with group mates’ pups. We used microsatellite markers to estimate relatedness and test whether kinship could explain this alloparental care and found that females were unrelated to the pups they guard. We conclude that females who reside in highly stable social groups exhibit cooperative behavior that cannot be explained by kinship and is unlikely to be due to direct or generalized reciprocity. Instead, our data suggest that alloparental care likely involves a complex interplay between group membership and cooperative foraging.