Strategic intergroup alliances increase access to a contested resource in male bottlenose dolphins

Richard C. Connor, Michael Krützen, Simon J. Allen, William B. Sherwin, Stephanie King

Research output: Contribution to journalArticle (Academic Journal)peer-review

11 Citations (Scopus)

Abstract

Efforts to understand human social evolution rely largely on comparisons with nonhuman primates. However, a population of bottlenose dolphins in Shark Bay, Western Australia, combines a chimpanzee-like fission-fusion grouping pattern, mating system, and life history with the only nonhuman example of strategic multilevel male alliances. Unrelated male dolphins form three alliance levels, or "orders", in competition over females: both within-group alliances (i.e., first- and second-order) and between-group alliances (third-order), based on cooperation between two or more second-order alliances against other groups. Both sexes navigate an open society with a continuous mosaic of overlapping home ranges. Here, we use comprehensive association and consortship data to examine fine-scale alliance relationships among 121 adult males. This analysis reveals the largest nonhuman alliance network known, with highly differentiated relationships among individuals. Each male is connected, directly or indirectly, to every other male, including direct connections with adult males outside of their three-level alliance network. We further show that the duration with which males consort females is dependent upon being well connected with third-order allies, independently of the effect of their second-order alliance connections, i.e., alliances between groups increase access to a contested resource, thereby increasing reproductive success. Models of human social evolution traditionally link intergroup alliances to other divergent human traits, such as pair bonds, but our study reveals that intergroup male alliances can arise directly from a chimpanzee-like, promiscuous mating system without one-male units, pair bonds, or male parental care.

Original languageEnglish
Article numbere2121723119
Pages (from-to)e2121723119
JournalProceedings of the National Academy of Sciences of the United States of America
Volume119
Issue number36
DOIs
Publication statusPublished - 6 Sept 2022

Bibliographical note

Funding Information:
ACKNOWLEDGMENTS. This dolphin research was carried out on Gathaagudu, Malgana Sea Country, and we acknowledge the traditional owners of the region. We thank RAC Monkey Mia Dolphin Resort and the Department of Biodiversity, Conservation and Attractions Shark Bay Rangers for their continued support and assistance. Permits for the scientific use of animals were obtained from the Department of Conservation and Land Management, Western Australia. The University of New South Wales provided ethics approval (UNSW ACEC 02/72, 05/76A). This study was supported by grants from the Australian Research Council A19701144 and DP0346313 to W.B.S. and R.C.C.; Swiss National Science Foundation 31003A_149956 to M.K.; The Eppley Foundation for Research to R.C.C.; Sea World Research and Rescue Foundation to R.C.C., M.K., and W.S.B.; W. V. Scott Foundation to M.K.; The National Geographical Society’s Committee for Research and Exploration; and the NSF (NSF 1316800). S.L.K. was supported by The Branco Weiss Fellowship—Society in Science. We also thank numerous field assistants, without whom this type of research would not be possible.

Publisher Copyright:
Copyright © 2022 the Author(s).

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