Philopatric Sex Research Articles

Evolution of sex differences in cooperation can be explained by trade-offs with dispersal.

Explaining the evolution of sex differences in cooperation remains a major challenge. Comparative studies highlight that offspring of the more philopatric sex tend to be more cooperative within their family groups than those of the more dispersive sex but we do not understand why. The leading "Philopatry hypothesis" proposes that the more philopatric sex cooperates more because their higher likelihood of natal breeding increases the direct fitness benefits of natal cooperation. However, the "Dispersal trade-off hypothesis" proposes that the more dispersive sex cooperates less because preparations for dispersal, such as extra-territorial prospecting, trade-off against natal cooperation. Here, we test both hypotheses in cooperatively breeding white-browed sparrow weavers (Plocepasser mahali), using a novel high-resolution automated radio-tracking method. First, we show that males are the more dispersive sex (a rare reversal of the typical avian sex difference in dispersal) and that, consistent with the predictions of both hypotheses, females contribute substantially more than males to cooperative care while within the natal group. However, the Philopatry hypothesis cannot readily explain this female-biased cooperation, as females are not more likely than males to breed within their natal group. Instead, our radio-tracking findings support the Dispersal trade-off hypothesis: males conduct pre-dispersal extra-territorial prospecting forays at higher rates than females and prospecting appears to trade-off against natal cooperation. Our findings thus highlight that the evolution of sex differences in cooperation could be widely attributable to trade-offs between cooperation and dispersal; a potentially general explanation that does not demand that cooperation yields direct fitness benefits.

Fine scale genetics reveals the subtle negative effects of roads on an endangered bat

The effective management of species with small and fragmented populations requires an in-depth understanding of how the effects of human-induced habitat disturbance shape the structure and gene flow at fine spatial scales. Identification of putative environmental barriers that affect individual exchange among subpopulations is imperative to prevent extinction risks. Here, we investigated how landscape affects the gene flow and relatedness structure of a population of the endangered lesser horseshoe bat (Rhinolophus hipposideros). We also assessed the effects of sexbiased dispersal on genetic relatedness. We genotyped 287 bat samples collected across southern Portugal and developed resistance surfaces for landscape variables hypothesized to affect gene flow. Then, we used spatially explicit models to fit relatedness distance through the resistance surfaces. We found genetic evidence of sex-biased dispersal and identified a significant fine scale structuring in the relatedness regarding females, the philopatric sex. Males displayed uniform levels of relatedness throughout the landscape. The results indicated less relatedness between the female´ from roosts located on proximity of roads than in roosts away from roads. Also, when analysing the sexes together the relatedness on roosts separated by highway were subtly less related in comparison to those occurring on the same side. Roads seem to be major shapers of the contemporary population structure of females, regardless of being relatively recent structures in the landscape. Furthermore, the relatedness patterns detected suggested that high tree density among roosts and continuity of forest patches in broader surrounding areas, promotes the relatedness among individuals. Landscape heterogeneity among roosts slightly decreases genetic relatedness. Nevertheless, those relationships are still weak, suggesting that population structuring driven by those factors is slowly ongoing. Thus, effective management measures should focus on issues for promoting safe road passages and suitable habitat corridors, allowing for the exchange of individuals and gene flow among lesser horseshoe bat roosts.

Facultative and persistent offspring sex-ratio bias in relation to the social environment in cooperatively breeding red-winged fairy-wrens (Malurus elegans)

Females should facultatively bias offspring sex ratio when fitness returns vary among sexes. In cooperative breeders, where individuals help raise others’ young, overproducing the philopatric sex will be adaptive when helpers are absent, whereas overproducing the dispersive sex may be adaptive to reduce intrasexual competition. Thus, fitness returns are expected to vary with the social environment. However, any offspring sex-ratio biases may also result from consistent among-female differences (e.g. quality) and/or environmental variables (e.g. food availability). Yet, few studies have disentangled facultative from persistent biases. We investigated offspring sex-ratio biases in relation to the social environment in cooperatively breeding red-winged fairy-wrens (Malurus elegans). Repeated observations of the same females over nine years allowed for disentanglement of facultative from persistent biases. Females without help did not overproduce daughters, despite female helpers being associated with higher fledgling survival (resource enhancement hypothesis). Instead, females without helpers facultatively overproduced sons —the slower dispersing sex— thereby ensuring long-term helper availability. Furthermore, offspring sex ratio was not biased towards the rarer sex of helpers present in the group or population (resource competition hypothesis). However, females with sex-biased helping produced similarly skewed offspring sex ratios. This among-female association may not be surprising, because helpers are previous seasons’ offspring. Thus, in addition to facultative responses to prevailing social conditions, we found evidence for persistent biases among females. This could potentially explain previous evidence for resource competition/enhancement that have typically been interpreted as facultative responses, highlighting the need for a within-female approach to better understand the adaptiveness of sex-ratio biases.Significance statementUnder certain conditions, females may benefit from producing a biased offspring sex ratio, but evidence for such effects in vertebrates is weak and inconsistent. Here, using observations of the same females under different social conditions, we show that cooperatively breeding red-winged fairy-wrens facultatively biased offspring sex ratio towards sons when living in pairs, thereby ensuring the availability of a workforce to assist in raising future offspring. However, biased offspring sex ratio patterns may also be the result of consistent differences among females. Indeed, we also found evidence for such patterns and suggest that this could be an explanation for previous findings which are often interpreted as facultative responses.

Repeated experimental removals unveil sex and age-specific dispersal strategies in a social passerine bird

Context Sex and age are frequently proposed as drivers of a number of behavioural and demographic patterns that can have important consequences for population dynamics including access to mates, sexual selection, parental care and lifetime productivity. Sex and age might also be important in shaping the movement patterns and colonisation processes of social species moving into vacant habitat. Such information is critical for the management of strongly interacting species such as the noisy miner (Manorina melanocephala), which structure ecological communities through aggressive exclusion of other taxa from areas that they occupy. Aims In Manorina colonies, young females are usually dispersive, while males remain in the natal colony as the philopatric sex. Following removal of individuals from an area, we aimed to determine whether female-biased dispersal, particularly of young females, would result in a more equal sex ratio and a younger age structure in the recolonising population. Methods These predictions were tested by anatomically ageing and sexing 1856 noisy miners that had been experimentally culled in two regions of New South Wales, Australia, to reduce the aggressive impact of this species on other native species. Key results Prior to removal, noisy miner populations were significantly male-biased in both regions (57% and 60%); however sex ratios after each of two removal episodes no longer differed from parity. Immature birds were a dominant feature (65%) of recolonising populations in both regions, however, the age structure of recolonising populations was different in each region, mostly likely due to the respective timing of culls during the year. Furthermore, the culling response in terms of age-specific sex ratio varied between regions. After the final cull, the sex ratio of mature birds had fallen to parity in one region but had become even more male biased (68%) in the other region. There was no sex-ratio bias among immature birds before or after culling. Conclusion These results confirm the expectation that immature birds are more likely to be colonisers, but the expectation of greater female dispersal was equivocal. Implications The differences in response between regions may reflect variation in population density, landscape connectivity or seasonality, highlighting challenges when implementing culling programs for conservation management.

Dispersal Alters the Nature and Scope of Sexually Antagonistic Variation.

AbstractIntralocus sexual conflict, or sexual antagonism, occurs when alleles have opposing fitness effects in the two sexes. Previous theory suggests that sexual antagonism is a driver of genetic variation by generating balancing selection. However, most of these studies assume that populations are well mixed, neglecting the effects of spatial subdivision. Here, we use mathematical modeling to show that limited dispersal changes evolution at sexually antagonistic autosomal and X-linked loci as a result of inbreeding and sex-specific kin competition. We find that if the sexes disperse at different rates, kin competition within the philopatric sex biases intralocus conflict in favor of the more dispersive sex. Furthermore, kin competition diminishes the strength of balancing selection relative to genetic drift, reducing genetic variation in small subdivided populations. Meanwhile, by decreasing heterozygosity, inbreeding reduces the scope for sexually antagonistic polymorphism due to nonadditive allelic effects, and this occurs to a greater extent on the X chromosome than autosomes. Overall, our results indicate that spatial structure is a relevant factor in predicting where sexually antagonistic alleles might be observed. We suggest that sex-specific dispersal ecology and demography can contribute to interspecific and intragenomic variation in sexual antagonism.

The Phylogenetic Roots of Human Kinship Systems

Nonhuman primates don’t have formal kinship systems, but genetic relatedness shapes patterns of residence, behavior, mating preferences, and cognition in the primate order. The goal of this article is to provide insight about the ancestral foundations on which the first human kinship systems were built. In order for evolution to favor nepotistic biases in behavior, individuals need to have opportunities to interact with their relatives and to be able to identify them. Both these requirements impose constraints on the evolution of kinship bonds in primate species. For nonhuman primates and many other mammals, maternal care generates close ties between mothers and offspring and among littermates. For species in which mother–offspring bonds extend beyond weaning, associations with the mother also generate familiarity among siblings of different ages. For species with female philopatry, mother–offspring ties provide the foundation for lifelong relationships between mothers and daughters, and dense matrilineal kin networks. However, several factors constrain the development of kinship bonds in nonhuman primates. First, dispersal strategies, which are designed to reduce inbreeding, bias kinship networks in favor of the philopatric sex. Second, hostile relationships between groups mean that kin ties are usually severed when individuals move from one group to another. Third, in species with polygynandrous mating systems, uncertainty about paternity and restricted periods of male reproductive monopoly limit the scope for development of ties among fathers and offspring, paternal siblings, or extended paternal kin networks. In this article, I explore the impact of these factors on the evolution of ancestral human kinship systems.

Consequences of maternal loss before and after weaning in male and female wild chimpanzees

The mother-offspring relationship is paramount in most mammals and infant survival often depends on maternal investment. In species with prolonged periods of development or co-residence, mothers may continue to influence their offspring’s outcomes beyond nutritional independence with benefits biased towards the philopatric sex. Chimpanzees (Pan troglodytes) are long-lived mammals with a protracted period of immaturity during which offspring continue to travel with their mothers. In contrast to most mammals, chimpanzees are also typically male philopatric. Here, we use over 50 years of demographic data from two communities in Gombe National Park, Tanzania, to examine the survival and longevity of both male and female chimpanzees that experienced maternal loss during three different age categories. Males who were orphaned between the ages of 0–4.99 years, 5–9.99 years, and 10–14.99 years all faced significantly lower survival than non-orphans and died earlier than expected. Females faced similarly reduced survival probabilities when orphaned between 0–4.99 and 5–9.99 years of age; however, females who experienced maternal loss between 10 and 14.99 years of age were no more likely to die than non-orphans. Females orphaned in this later age class also lived significantly longer beyond maternal loss than their male counterparts. As observed in other mammals, philopatric male chimpanzees may continue to benefit from their mother’s ecological knowledge, whereas maternal influence on female offspring likely fades as they prepare to emigrate. These results emphasize how maternal influence on offspring outcomes can extend well beyond weaning, particularly for the philopatric sex. Mammalian mothers are crucial to their infant’s survival and in species where offspring continue to live with their mothers after weaning, maternal influence may extend beyond dependence on mother’s milk. While in most group-living mammals females remain in their natal group, chimpanzees typically display the opposite pattern with males residing alongside their mothers into adulthood. Using over 50 years of data on wild chimpanzees, we investigated the consequences of maternal loss both before and after weaning. We found that both males and females orphaned up to 10 years of age were less likely to survive than non-orphans; however, only males orphaned between 10 and 15 years also faced lower survival. These results emphasize how chimpanzee mothers continue to matter for offspring beyond infancy and provide novel data on reduced maternal influence on survival for daughters compared to sons.

The effect of social and ecological factors on the time budget of wild vervet monkeys

AbstractAnimals often have a limited time to perform different fitness‐enhancing activities, such as the trade‐off between socializing versus foraging in group‐living species. Many previous studies have focused on how ecological and social factors influence activity budget at the individual or group level in various species. However, few primate studies have focused on multiple study groups living within a similar habitat. Here, we analyse group, season and sex effects on the individual activity budget of wild vervet monkeys (Chlorocebus pygerythrus) living in four groups with overlapping home ranges. Generally, our findings support previous studies on primates. Our results indicate that intragroup competition may force larger groups to spend more time feeding and less time resting. We also found that seasonal variation, and therefore food availability, has a strong influence on the monkeys’ activity budget. Females, which are the philopatric sex in vervet monkeys, spent more time socializing while, in general, males spent more time resting. However, we did not find any difference on the time spent socializing between groups. Since there is evidence that not only time constraints and habitat quality but also group size influence individual behaviours and ultimately group living, we advise that future studies should focus on multiple groups of the same species living in the same habitat in order to better understand how all these variables are interlinked.

Social attention biases in juvenile wild vervet monkeys: implications for socialisation and social learning processes.

The concept of directed social learning predicts that social learning opportunities for an individual will depend on social dynamics, context and demonstrator identity. However, few empirical studies have examined social attention biases in animal groups. Sex-based and kinship-based biases in social learning and social attention towards females have been shown in a despotic and female philopatric primate: the vervet monkey (Chlorocebus pygerythrus). The present study examined social attention during the juvenile period. Social attention was recorded through 5-min focal observations during periods of natural foraging. Kin emerged as the most important focus of social attention in juveniles, intensified by biased spatial proximity towards matrilineal related members. The highest-ranking conspecifics were more frequently observed by juveniles than low-ranking ones. Additionally, younger and orphaned juveniles showed higher levels of social attention overall, compared to other age categories. No effect of the juvenile's hierarchical rank was detected, suggesting that the variation in social attention recorded reflects different biases and stages of social learning and socialisation, rather than social anxiety. Juvenile females tended to exhibit a dominance-based bias more strongly than did males. This might be explained by a greater emphasis on attaining social knowledge during juvenile socialisation in the philopatric sex. Moreover, despite a preferred association between juveniles, social attention was more often directed to adults, suggesting that adults may still be more often chosen as a target of attention independent of their dominance rank.

Behavioural patterns of vocal greeting production in four primate species.

Social animals have evolved a range of signals to avoid aggressive and facilitate affiliative interactions. Vocal behaviour is especially important in this respect with many species, including various primates, producing acoustically distinct ‘greeting calls’ when two individuals approach each other. While the ultimate function of greeting calls has been explored in several species, little effort has been made to understand the mechanisms of this behaviour across species. The aim of this study was to explore how differences in individual features (individual dominance rank), dyadic relationships (dominance distance and social bond strength) and audience composition (presence of high-ranking or strongly bonded individuals in proximity), related to vocal greeting production during approaches between two individuals in the philopatric sex of four primate species: female olive baboons (Papio anubis), male chimpanzees (Pan troglodytes), female sooty mangabeys (Cercocebus atys) and female vervet monkeys (Chlorocebus pygerythrus). We found that female vervet monkeys did not produce greeting calls, while in the other three species, low-ranking individuals were more likely to call than high-ranking ones. The effects of dyadic dominance relationships differed in species-specific ways, with calling being positively associated with the rank distance between two individuals in baboons and chimpanzees, but negatively in mangabeys. In none of the tested species did we find strong evidence for an effect of dyadic affiliative relationships or audience on call production. These results likely reflect deeper evolutionary layers of species-specific peculiarities in social style. We conclude that a comparative approach to investigate vocal behaviour has the potential to not only better understand the mechanisms mediating social signal production but also to shed light on their evolutionary trajectories.

Payoff- and Sex-Biased Social Learning Interact in a Wild Primate Population

Social learning in animals is now well documented, but few studies have determined the contexts shaping when social learning is deployed. Theoretical studies predict copying of conspecifics gaining higher payoffs [1-4], a bias demonstrated in primates only in captivity [5]. In the wild, research has shown selective attention toward the philopatric sex, a group's stable core [6]. Here, we report the first rigorous experimental test of the existence of a payoff bias in wild primates and its interaction with the sex of the model. We created a payoff bias in which an immigrant alpha male in each of three groups of wild vervet monkeys received five times more food upon opening a foraging box than did the philopatric alpha female, whereas in two control groups, male and female models received the same amount of food. We tested whether this payoff asymmetry would override thepreviously documented selective learning from resident females. Group members were tested after having watched both models. When both models received the same amount of food, audience members copied the female model significantly more than the male model, confirming previous findings. However, when a marked payoff bias was introduced, male, but not female, vervet monkeys significantly more often copied the male model receiving a higher payoff. These results demonstrate behavioral flexibility in the dispersing sex in these primates and suggest that the philopatric sex can afford to be more conservative in their social learning. Our findings show that multiple social-learning biases can coexist and interact within the same species.

Demography and life history of a group of white-bellied spider monkeys (Ateles belzebuth) in western Amazonia.

Species-specific demographic parameters and life history variables are important for understanding how individual primate taxa have adapted to evolutionary and ecological pressures and for conducting interspecific comparisons as well as for conducting population viability analyses and for managing captive populations. Here, we describe results from a 12+ year study of the demographic dynamics of a wild group of white-bellied spider monkeys (Ateles belzebuth belzebuth) living near the Tiputini Biodiversity Station in a largely pristine rainforest in western Amazonia. Across the study period, group size varied between 25 and 37 individuals, and there was a clearly female-biased sex ratio within all age classes. Females were the dispersing sex, as 19 females born into the group disappeared close to reaching adult body size and were presumed to have emigrated, while seven subadult or adult females joined the group during the study period. We estimated the age of dispersal for females at 5.9 ± SD 0.4 years (N = 13). Our study confirms that males are the philopatric sex, as all natal males have remained in the group and some have begun to reproduce, while no males have immigrated. Males began ranging independently from their mothers at ∼4.5 years of age and began copulating with adult females by the age of ∼5 years. Females had long inter-birth intervals (44.2 ± SD 7.8 months; range: 32-64 months, N = 21). Based on our data, female spider monkeys might have longer life spans than males, as only one out of six adult males but 9 out of 11 adult females present in the group in mid 2005 were still present in January 2018. The slow development and extended life histories of wild spider monkeys pose significant challenges for the ability of these primates to cope with habitat degradation and hunting throughout their geographical distribution.

The influence of a demographic change on social relationships among male golden snub-nosed monkeys (Rhinopithecus roxellana).

It has been suggested that social relationships are more likely to be prone to variation in the dispersing sex than the philopatric sex. However, we know less about the dynamics of all-male groups in male-dispersing species than we do about other types of primate groups. We studied male sociality in a captive group of golden snub-nosed monkeys (Rhinopithecus roxellana), which was composed of a one-male unit (OMU, N = 7) and an all-male unit (AMU, N = 7 or 8), in Shanghai Wild Animal Park, China. Using data collected for 6months, during which there was a demographic change in the AMU and the alpha male was replaced by a newcomer, we found that a dramatic change in social ranks occurred accompanied by elevated aggression following this social upheaval. A proximity-based social network analysis revealed that members did not associate randomly any more but formed differentiated relationships post-upheaval, resulting in three distinct sub-units in the AMU. In terms of inter-unit interactions, significant changes were found in the affiliations between the male juvenile of OMU and AMU individuals. He interacted with AMU individuals randomly and frequently pre-upheaval, but cut down his affiliations and had a preferred partner post-upheaval, who was a member of the dominant male's sub-unit. Our findings suggest that social networks in the dispersing sex are dynamic structures and vary by some demographic change (e.g., individual immigration) in the studied species. We also put forward that individual dominance could be a criterion when the male juvenile chooses partners before he immigrates into a group. In conclusion, the high level of behavioral flexibility of the dispersing sex could be an evolutional strategy and good for individuals' future dispersing life.

Social network dynamics precede a mass eviction in group-living rhesus macaques

Network dynamics can reveal information about the adaptive function of social behaviour and the extent to which social relationships can flexibly respond to extrinsic pressures. Changes in social networks occur following changes to the social and physical environment. By contrast, we have limited understanding of whether changes in social networks precede major group events. Permanent evictions can be important determinants of gene flow and population structure and are a clear example of an event that might be preceded by social network dynamics. Here we examined the social networks of a group of rhesus macaques, Macaca mulatta, in the 2 years leading up to the eviction of 22% of adult females, which are the philopatric sex. We found that females engaged in the same amount of aggression and grooming in the 2 years leading up to the eviction but that there were clear changes in their choice of social partners. Females that would eventually be evicted received more aggression from lower-ranking females as the eviction approached. Evicted females also became more discriminating in their grooming relationships in the year nearer the split, showing a greater preference for one another and becoming more cliquish. Put simply, the females that would later be evicted continued to travel with the rest of the group as the eviction approached but were less likely to interact with other group members in an affiliative manner. These results have potential implications for understanding group cohesion and the balance between cooperation and competition that mediates social groups.

Socio-genetic correlates of unbiased sex dispersal in a population of black capuchin monkeys (Sapajus nigritus)

Most social mammal species exhibit male-biased dispersal. Sex bias in dispersal leads to a higher degree of relatedness among individuals of the philopatric sex, thus an atypical dispersal pattern might lead to deviations in the typical within-group kinship structure. Kinship, in turn, influences patterns of social interactions, as widely evident by kin-biased behaviors. We investigated the link between dispersal, relatedness structure, and sociopositive interactions established by adult females of black capuchin monkeys (Sapajus nigritus) living in a population that experiences female dispersal, an unusual pattern for capuchin monkeys. The study was conducted in Parque Estadual Carlos Botelho (PECB), within the Brazilian Atlantic Forest. We addressed dispersal and relatedness patterns by genotyping 20 adults of 3 groups across 9 microsatellite loci. We also sampled the monkeys’ behavior and compared spatial association frequencies and rates of grooming among same- and opposite-sex dyads. There was no difference between males and females in genetic parameters; both males and females show low coefficients of relatedness indicating that neither sex is consistently philopatric. The mean pairwise coefficient of relatedness for co-resident females was not higher than that for co-resident males. Compared to other populations of capuchin monkeys, female bond was weak, as evident by lower spatial association frequencies, reduced rates of grooming and lack of correlation between coefficients of relatedness and measures of dyadic sociopositive interactions. Our findings thus confirm that female dispersal is a habitual process in the capuchin population of PECB, and that, as expected, dispersal by females strongly influences the relatedness structure of the population as well as the affiliative relationships among female groupmates.

Sex‐biased dispersal and spatial heterogeneity affect landscape resistance to gene flow in fisher

AbstractGenetic connectivity results from the dispersal and reproduction of individuals across landscapes. Mammalian populations frequently exhibit sex‐biased dispersal, but this factor has rarely been addressed in individual‐based landscape genetics research. In this study, we evaluate the effects of sex‐biased dispersal and landscape heterogeneity on genetic connectivity in a small and isolated population of fisher (Pekania pennanti). We genotyped 247 fisher samples collected across the southern Sierra Nevada Mountains of California. We tested for genetic evidence of sex‐biased dispersal using sex‐specific population structure and spatial autocorrelation analyses, and sex‐biased dispersal tests of the assignment index, FST, and FIS. We developed resistance surfaces for eight landscape features hypothesized to affect gene flow and optimized each resistance surface independently by sex. Using multiple regression of distance matrices and an information‐theoretic model selection approach, we fit models of genetic distance to landscape resistance distance separately by sex and geographic region. We found genetic evidence of sex‐biased dispersal with significant differences in FST, FIS, and spatial autocorrelation between sexes. Optimal resistance values differed by sex, and model variables, fit, and parameter estimates varied substantially both between sexes and between geographic regions. We found a stronger relationship between landscape features and genetic distance for females, the philopatric sex, than the more widely dispersing males. Our results show that landscape features influencing gene flow differed by both sex and regional heterogeneity. Conducting analyses by sex and by region allowed for the identification of landscape genetics relationships not discernible when analyzed together. Our results show that failing to account for these factors can confound results and obscure relationships between landscape features and gene flow.

Adult meerkats modify close call rate in the presence of pups.

In animals, signaling behavior is often context-dependent, with variation in the probability of emitting certain signals dependent on fitness advantages. Senders may adjust signaling rate depending on receiver identity, presence of audiences, or noise masking the signal, all of which can affect the benefits and costs of signal production. In the cooperative breeding meerkat Suricata suricatta, group members emit soft contact calls, termed as “close calls”, while foraging in order to maintain group cohesion. Here, we investigated how the close calling rate during foraging was affected by the presence of pups, that produce continuous, noisy begging calls as they follow older group members. Adults decreased their overall close call rate substantially when pups were foraging with the group in comparison to periods when no pups were present. We suggest this decrease was likely due to a masking effect of the loud begging calls, which makes the close call function of maintaining group cohesion partly redundant as the centrally located begging calls can be used instead to maintain cohesion. There was some support that adults use close calls strategically to attract specific pups based on fitness advantages, that is, as the philopatric sex, females should call more than males and more to female pups than male pups. Dominant females called more than dominant males when a pup was in close proximity, while subordinates showed no sex-based differences. The sex of the nearest pup did not affect the calling rate of adults. The study shows that meerkats modify their close call production depending on benefits gained from calling and provides an example of the flexible use of one calling system in the presence of another, here contact calls versus begging calls, within the same species.

How Sex-Biased Dispersal Affects Sexual Conflict over Care

Existing models of parental investment have mainly focused on interactions at the level of the family and have paid much less attention to the impact of population-level processes. Here we extend classical models of parental care to assess the impact of population structure and limited dispersal. We find that sex differences in dispersal substantially affect the amount of care provided by each parent, with the more philopatric sex providing the majority of care to young. This effect is most pronounced in highly viscous populations: in such cases, when classical models would predict stable biparental care, inclusion of a modest sex difference in dispersal leads to uniparental care by the philopatric sex. In addition, mating skew also affects sex differences in parental investment, with the more numerous sex providing most of the care. However, the effect of mating skew holds only when parents care for their own offspring. When individuals breed communally, we recover the previous finding that the more philopatric sex provides most of the care even when it is the rarer sex. We conclude that sex-biased dispersal is likely to be an important yet currently overlooked driver of sex differences in parental care.

The ties that bind: Maternal kin bias in a multilevel primate society despite natal dispersal by both sexes.

In many social animals, individuals derive fitness benefits from close social bonds, which are often formed among kin of the philopatric sex. Hamadryas baboons, however, exhibit a hierarchical, multilevel social system where both sexes disperse from their natal one-male-unit (OMU). Although this would seem to hinder maintenance of kin ties, both sexes appear largely philopatric at the higher order band and clan levels, possibly allowing for bonds with same sex kin by both males and females. In order to investigate the possibility of kin bonds in hamadryas baboons, we identified kin dyads in a band without known pedigree information using a large panel of genetic markers: 1 Y-linked, 4 X-linked, and 23 autosomal microsatellites and part of the mitochondrial hypervariable region I. With these data, we performed a kinship analysis while accounting for misclassification rates through simulations and determined kinship among two types of dyads: leader and follower males and female dyads within OMUs. Leader and follower males were maternal relatives more often than expected by chance, suggesting that kinship plays a role in the formation of these relationships. Moreover, maternal female relatives were found in the same OMU more often than expected by chance, indicating that females may be motivated to maintain post-dispersal contact with maternal female kin. Our results suggest that hamadryas baboons can recognize maternal kin and that kin selection has contributed to shaping their complex social system. This implies that an ancestral maternal kin bias has been retained in hamadryas society. Am. J. Primatol. 78:731-744, 2016. © 2016 Wiley Periodicals, Inc.

Female House Mice do not Differ in Their Exploratory Behaviour from Males

AbstractDispersal is an important ecological trait affecting genetic variation and dynamics of populations. Hence, the exploratory behaviour prior to actual dispersal may be crucial for potentially dispersing individuals. In mammals, females are traditionally seen as the more philopatric sex and dispersal as male‐biased behaviour, and so behavioural strategies related to the exploration of novel resources should be differentially expressed in males and females. In addition, due to sexual selection exploratory strategies may be expected to vary according to females’ reproductive phase. We employed a standard open‐field test as an approximation of the first phase of dispersal, using adult house mice representing two subspecies, M. m. musculus and M. m. domesticus. We tested the prediction that exploration of neutral area varies in females during different phases of the oestrus cycle and is different between both sexes and subspecies. We expected to find higher exploration in males, as the more dispersing sex and less pronounced subspecies‐specific differences in females than in males. We found no significant effect of the oestrous phase on any of the parameters of the exploratory behaviour measured. Sexual dimorphism was found only in latency to enter the arena in M. m. domesticus where females hesitated longer to enter a new area than males. Significant subspecies‐specific differences were found in three of four tested exploration parameters, so we conclude that females of both subspecies follow similar strategies to those displayed by males. Musculus mice show shorter latency to enter a new area, but once inside, domesticus mice explore the arena significantly longer, with less frequent retreats to a shelter. Our results thus highlight that the role of female dispersal in interdemic gene flow should not be neglected.