Benefits of living closer to kin vary by genealogical relationship in a territorial mammal

Female philopatry may influence antipredatory behavior in a solitary mammal

Whether neighboring individuals are related or not has a number of important ecological & evolutionary ramifications. Kin selection resulting from philopatry can play an important role in social and antipredatory behavior. Ground squirrels exhibit alarm vocalizations in the presence of predators; however, the degree to which kin selection shapes alarm calling behavior varies with species ecology and the degree of relatedness between neighbors. We studied a solitary ground squirrel species that exhibits sex-biased calling propensity to determine if female philopatry may be responsible for sex differences in antipredatory behavior observed in our population. We used double digest restriction-site associated DNA sequencing (ddRADseq) to sample the genomes of Harris's antelope squirrel (Ammospermophilus harrisii) to determine the relatedness between individuals and test whether genetic and geographic distance were correlated. We found that geographic distance had a positive relationship with genetic distance, and that this relationship was sex-dependent, suggesting male-biased dispersal. Our results provide supporting evidence that female philopatry may be responsible for higher calling propensity observed in female squirrels, potentially influencing antipredatory behavior in this species via kin selection. Our findings add to a growing body of evidence that philopatry is an important ecological driver influencing sociospatial organization in solitary species.

Should sons breed independently or help? Local relatedness matters

In cooperatively breeding birds, why do some individuals breed independently but others have to help at home? This question has been rarely addressed despite its fundamental importance for understanding the evolution of social cooperation. We address it using 15 years of data from Tibetan ground tits Pseudopodoces humilis where helpers consist of younger males. Since whether younger males successfully breed depends critically on their chances to occupy territories nearby home, our analytic strategy is to identify the determinants of individual differences in gaining territory ownership among these ready-to-breed males. Across widowed, last-year helper and yearling males, an age advantage was evident in inheriting resident territories, occupying adjacent vacancies and budding off part of adjacent territories, which left some last-year helpers and most yearling males to take the latter two routes. These males were more likely to acquire a territory if they were genetically related to the previous or current territory owners; otherwise they remained on natal territories as helpers. The relatedness effect can arise from the prior residence advantage established in the preceding winter when younger males followed their parents to perform kin-directed off-territory forays. Our research highlights the key role of local kinship in determining younger males' territory acquisition and thus their fate in terms of independent reproduction versus help. This finding provides insight into the formation of kin-based, facultative cooperative societies prevailing among vertebrates.