The 84th Annual Meeting of the American Association of Physical Anthropologists (2015)


The effects of paternity and male rank on male-immature relationships in the mountain gorilla (Gorilla beringei beringei)

STACY ROSENBAUM1, JOAN B. SILK2, JEAN PAUL HIRWA3, LINDA VIGILANT4 and TARA S. STOINSKI3,5.

1Davee Center for Epidemiology & Endocrinology, Lincoln Park Zoo, 2Institute for Human Origins, Arizona State University, 3Dian Fossey Gorilla Fund International, 4Department of Primatology, Max Planck Institute for Evolutionary Anthropology, 5Zoo Atlanta

March 26, 2015 11:45, Grand Ballroom E/F/G Add to calendar

Kin discrimination mechanisms are expected to evolve when they provide fitness benefits. In species with promiscuous mating systems, males were long believed to abstain from parenting behaviors partly because the costs of potential offspring misidentification outweighed the benefits of dual parenting. Recent work has shown that in some species males parent despite high rates of false paternity, and males in some promiscuous systems discriminate between their own and other males’ offspring. Adult male mountain gorillas (Gorilla beringei) and immatures in their groups have close relationships even when paternity certainty is low, and such relationships are best explained as low-cost parenting behavior. Using an information theoretic approach, we evaluated the impact of rank and paternity on male/immature relationships in wild multi-male gorilla groups monitored by the Dian Fossey Gorilla Fund’s Karisoke Research Center. In our sample of 21 adult males and 50 genotyped immatures, males and 1-5 year old immatures clearly use rank, not paternity, to choose preferred social partners. Males and immatures were closer social partners in 2011-12 when reproductive skew was low and group size smaller than in 2003-04 when skew was high and group size larger. Gorillas’ lack of paternal kin discrimination provides further behavioral evidence that the species’ multi-male social structure is evolutionarily novel. However, patterning of male-immature relationships and genetic paternity suggest a persistent minority of bi-male groups throughout Gorilla beringei’s evolutionary history. This may help explain their ability to live for extended periods in multi-male, multi-female social units despite possessing morphological characteristics typical of harem systems.

This work was funded by the National Science Foundation (Doctoral Dissertation Grant #1122321), the Wenner-Gren Foundation, and the Leakey Foundation.