Mating in a bisexually philopatric society: bottlenose dolphin females associate with adult males but not adult sons during estrous
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In fission-fusion societies, group size and composition change dynamically, reflecting social preferences and pressures. Most notably during reproduction, intersexual group dynamics reflect a balance between female choice for optimal mates and male competition for mating access. In systems where males and females remain in their natal area for life (bisexual philopatry), females can reduce the risk of incest by avoiding mating or associating with male kin. Shark Bay bottlenose dolphins (Tursiops aduncus) live in fission-fusion societies that enable them to exercise age, sex, and kin association biases. To determine how the balance between female choice and male competition is achieved, we examined adult female association with juvenile and adult males, including sons during female receptive periods, using 30 years of longitudinal data. Adult females demonstrated an increase in adult male association just prior to known conceptions, while juvenile male association consistently remained low. A decline in male association post-conception suggests that one or both sexes detect pregnancy early on. When we examined female association with juvenile and adult sons, a distinct pattern emerged. Adult females preferentially associated with sons compared to non-sons of the same age class post-weaning. Strikingly, females rarely associated with their adult sons when cycling. Our results suggest that (1) adult males either out-compete juvenile males in gaining access to fertile females or females prefer adult to juvenile males and (2) females mitigate the risk of close inbreeding by reducing association with sons when cycling.
No study has investigated behavioral strategies for reducing close inbreeding in bisexually philopatric, fluid mammal societies outside of humans. Using over 30 years of longitudinal data, we document how association dynamics change with female reproductive state. Post-weaning, mothers and sons associate, but almost never during conceptive periods. Adult male–female association is frequent during estrous, with a sharp decline after conception. Our study provides evidence for long-term kin recognition and detection of both estrous and early pregnancy among wild bottlenose dolphins. These findings have implications for the evolution of bisexual philopatry, fission-fusion dynamics, and infanticide—or lack thereof—in mammals.
KeywordsBisexual philopatry Estrous Inbreeding Juvenile Pregnancy Tursiops
We thank current and past members of the Shark Bay Dolphin Project, and numerous field assistants, for their efforts in data collection used for this project. In particular, we would like to acknowledge Ann-Marie Jacoby, Sara Eshleman, Jillian Wisse, Desirae Cambrelen, and Theodora Efthymiou. We are grateful to the Western Australia Department of Parks and Wildlife (DPaW) and the Monkey Mia Dolphin Resort for their logistical support in the field. We thank DPaW for contributing a portion of the life history data. We also thank two anonymous reviewers for their input on an earlier version of this manuscript. The study was funded by National Science Foundation grants 0941487, 0918308, 0316800, National Geographic Society Committee for Research and Exploration, ONR BAA 10230702, and Georgetown University.
Compliance with ethical standards
This work was approved by the Georgetown University Animal Care and Use Committee, permits #07–041, #10–023, #13-069, Western Australia Department of Parks and Wildlife permit #SF007418, #SF007975, #SF006897, #SF007457, #SF009311, #SF008076, #SF009876, and The University of Western Australia animal ethics permit #600-37. All procedures performed in this study were in accordance with the ethical standards of the aforementioned institutions and agencies. The study was funded by National Science Foundation grants 0941487, 0918308, 0316800, National Geographic Society Committee for Research and Exploration, ONR BAA 10230702, and Georgetown University.
Conflict of interest
The authors declare that they have no conflict of interest.
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