Kinship and association in a highly social apex predator population, killer whales at Marion Island

• Published in: Behavioral Ecology
• Main Authors: Reisinger, Ryan Rudolf, Beukes, Charlene, Hoelzel, A. Rus, De Bruyn, P.J. Nico
• Format: Article in Journal/Newspaper
• Language: English
• Published: Oxford University Press 2017
• Subjects: Delphinids; Group; Network; Predators; Relatedness; Sociality; Social structure; Socio-ecology; Antarctic; Southern Ocean; Antarc*; Marion Island; Orca; Orcinus orca; South African National Antarctic Programme
• Online Access: http://hdl.handle.net/2263/61373; https://doi.org/10.1093/beheco/arx034

Social structure is a core element of population biology, influenced by intrinsic and environmental factors. Intra-taxon comparisons of social organization are useful in elucidating the role of such ecological determinants of sociality. Killer whales Orcinus orca are widely distributed, social delphinids with diverse morphology, diet, behaviour, and genetics, but few studies have quantitatively examined social structure in this species. We used 7 years of individual identification data on killer whales at Marion Island, Southern Ocean, to calculate the half-weight association index among 39 individuals, creating a weighted association network. There were long-term associations between individuals, though associations were dynamic over time. We defined 8 social modules using a community detection algorithm and these typically contained 3 individuals of various ages and sexes. Pairwise genetic relatedness among 20 individuals was not significantly correlated with association index. Individuals were on average more related within than between social modules, but social modules contained related as well as unrelated individuals. Likely parent pairs of 6 individuals indicated mating between social modules. The South African National Research Foundation (NRF) Thuthuka programme (grant number 76230), the NRF South African National Antarctic Programme (grant numbers 80271, 93071), the Mohamed bin Zayed Species Conservation Fund (project number 10251290), the International Whaling Commission’s Southern Ocean Research Partnership and an NRF South African Network for Coastal and Oceanic Research post-doctoral fellowship to RRR (grant number 94916). http://beheco.oxfordjournals.org 2018-05-30 hj2017 Mammal Research Institute Zoology and Entomology