Distribution of genetic paternity in primate groups

Understanding the distribution of paternity within social groups is critical for testing hypotheses about the evolution of behavior and morphology in primates, but assembling the requisite comparative data is a challenging task. We compiled genetic paternity data from 52 species of wild nonhuman primates along with information about socioecological, morphological, and life history traits that are relevant to understanding what proportion of offspring are sired by primary males (i.e., alpha males in multi-male groups and resident males in single male groups). Our dataset, which currently contains information about 11 primate families and >3,000 individual paternities, is presented as a publicly accessible, living database designed to be updated as new data become available. Using Bayesian regression models, we investigated the role that phylogeny, group composition, and seasonality play in determining primary males paternity share, and assessed the relative share of paternities obtained by non-primary residents versus extra-group males. First, we found that phylogeny has a detectable but relatively modest influence on primary males paternity share. Species-level differences explained roughly 35-40% of variation in primary males paternity share, and of that interspecific variation, [~]50-70% was attributable to shared phylogenetic history. Second, group composition strongly predicted paternity share outcomes. Primary males in single-male/multi-female groups obtained the highest share of paternity ([~]80%), while those in multi-male groups had the lowest ([~]60%), though there was substantial variation within each category. Pair-living animals showed a striking split: males in cohesive pairs sired [~]90% of offspring, while those in dispersed pairs sired only [~]55%. Contrary to expectations, reproductive seasonality did not predict primary males paternity share in any group type. Finally, when primary males in multi-male groups lost paternities, [~]75% of losses were to other resident males. Overall, [~]5-15% of offspring in these groups were sired by extra-group males. Our results largely confirm earlier findings based on smaller datasets, but also show that the relationship between social organization and paternity is more complicated than simple categorical predictions suggest. We discuss the gap between the data that would ideally be available for testing these hypotheses versus what currently exists, with hopes that our living database can help close this gap over time.