title: Mothers may shape the variations in social organization among gorillas.
abstract: When mothers continue to support their offspring beyond infancy, they can influence the fitness of those offspring, the strength of social relationships within their groups, and the life-history traits of their species. Using up to 30 years of demographic data from 58 groups of gorillas in two study sites, this study extends such findings by showing that mothers may also contribute to differences in social organization between closely related species. Female mountain gorillas remained with their sons for significantly longer than western gorillas, which may explain why male philopatry and multimale groups are more common among mountain gorillas. The presence of the putative father and other familiar males did not vary significantly between species, and we found only limited support for the socio-ecological theory that the distribution of adult males is influenced by the distribution of females. Within each gorilla species, variations in those distributions may also reflect the different stages in the typical life cycle of a group. Collectively, our results highlight the potentially far-reaching consequences of maternal support that extends beyond infancy, and they illustrate the opportunity to incorporate additional factors into phylogenetic analyses of variations in social organization, including studies of human evolution.
authors.affiliation: Max Planck Institute for Evolutionary Anthropology , Deutscher Platz 6, 04103 Leipzig , Germany.
authors.forename: Andrew M
authors.identifier: 0000-0001-8913-3536
authors.initials: AM
authors.lastname: Robbins
authors.affiliation: Formerly with the International Gorilla Conservation Programme , PO Box 931, Kigali , Rwanda.
authors.forename: Maryke
authors.initials: M
authors.lastname: Gray
authors.affiliation: Wildlife Conservation Society, Global Conservation Program, 2300 Southern Boulevard, Bronx, NY 10460, USA; Mbeli Bai Study, Wildlife Conservation Society-Congo Program, BP 14537 Brazzaville, Republic of Congo.
authors.forename: Thomas
authors.initials: T
authors.lastname: Breuer
authors.affiliation: Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany; Mbeli Bai Study, Wildlife Conservation Society-Congo Program, BP 14537 Brazzaville, Republic of Congo.
authors.forename: Marie
authors.initials: M
authors.lastname: Manguette
authors.affiliation: Wildlife Conservation Society , Global Conservation Program , 2300 Southern Boulevard, Bronx, NY 10460 , USA.
authors.forename: Emma J
authors.initials: EJ
authors.lastname: Stokes
authors.affiliation: Volcanoes National Park , Rwanda Development Board , PO Box 6239, Gishushu, Kigali , Rwanda.
authors.forename: Prosper
authors.initials: P
authors.lastname: Uwingeli
authors.affiliation: Parc National des Virunga-sud , Institut Congolais pour la Conservation de la Nature , c/o IGCP-DRC, B.P. 137 Gisenyi , Rwanda.
authors.forename: Innocent
authors.initials: I
authors.lastname: Mburanumwe
authors.affiliation: Formerly with the Mgahinga Gorilla National Park , Uganda Wildlife Authority , PO Box 3530, Kampala , Uganda.
authors.forename: Edwin
authors.initials: E
authors.lastname: Kagoda
authors.affiliation: Max Planck Institute for Evolutionary Anthropology , Deutscher Platz 6, 04103 Leipzig , Germany.
authors.forename: Martha M
authors.initials: MM
authors.lastname: Robbins
keywords: dispersal; human evolution; life history; maternal investment; multimale groups; philopatry