Intragroup genetic relatedness in two howler monkey species (Alouatta pigra and A. palliata): Implications for understanding social systems and dispersal

Abstract

Social systems and dispersal patterns impact genetic variation within and between primate groups. Kinship plays a role in shaping social interactions and therefore shapes social systems. However, few studies have used molecular data to describe the degree of genetic relatedness among intragroup individuals. In this study, I analyze genetic relatedness among same-sex intragroup adults in Alouatta palliata and A. pigra, sister species that have distinct social systems, to test the hypothesis that patterns of intragroup genetic relatedness will also be distinct. Results indicate that in both species, most groups contain closely related same-sex dyads, which was unexpected for A. palliata since it has been reported that most juveniles disperse and join groups that do not contain close kin. However, the degree of intragroup relatedness seems to be more variable among A. pigra groups, whereas most same-sex adults are closely related in A. palliata groups. This suggests that dispersing individuals may use multiple strategies to join groups (i.e., coalition take overs by related males, solitary individuals joining groups that contain close relatives, etc.) or that philopatry is common in these groups. Further study including both long-term observational and genetic data is necessary to determine the degree of variation in intragroup genetic relatedness for both species within and among populations and fitness consequences of various strategies. Ecological and demographic data are also necessary to determine the importance of other factors, especially habitat fragmentation, in determining the degree of relatedness in howler monkey groups.