Evaluating the influence of ecology, sex and kinship on the social structure of resident coastal bottlenose dolphins
Animal social structures are shaped by external environmental factors and individual intrinsic behavioral traits. They represent a balance between the costs and benefits of group-living to maximize individual fitness. Bottlenose dolphin, Tursiops truncatus, societies are fission–fusion with high variations in association strength, grouping patterns and influence of kinship on social bonds throughout the wide range of habitats where they occur. Here, the drivers of social structure in resident coastal bottlenose dolphins of the Normano-Breton Gulf (English Channel) were studied using a multidisciplinary approach combining individual monitoring (photo-identification) information, genetic and ecological data. First, the ecological segregation of the social clusters was tested. Then, the influence of kinship, sex and ecological specializations on association patterns was evaluated. Stable isotopes revealed that the social clusters had relatively distinct ecological niches. Resource partitioning among social clusters may reduce competition and may allow the area to sustain a larger resident bottlenose dolphin population. Individuals did not preferentially associate with related individuals or individuals of the same sex. However, sample size was relatively low for females and, therefore, a role of kinship in shaping association patterns could not be totally ruled out for those individuals. Instead, dolphins preferentially associated with individuals of similar ecology. The study also emphasizes that stable isotope analysis is a promising tool to investigate the link between social structure and ecological specializations, particularly in taxa that are difficult to observe in the wild.
We thank GECC volunteers for help in the field. We are grateful to Tiphaine Chouvelon, Paula Mendez-Fernandez and Paul Tixier for advices on sample preparation for the isotopic analyses, and to Gaël Guillou and Pierre Richard for stable isotope analyses. We also thank the Molecular Core Facility at the University of La Rochelle, and Vanessa Becquet and Eric Pante for advices on molecular work. We are also grateful to Conor Ryan for advices on statistical analyses of stable isotope data. We thank Amy Lusher for English language revisions of the manuscript. This work was supported by Fondation Total, Agence de l’Eau Seine-Normandie, Fonds de Dotation pour la Biodiversité, Agence des Aires Marines Protégées, Direction Régionale de l’Environnement, de l’Aménagement et du Logement, Ministère de l’Ecologie, du Développement Durable et de l’Energie and Conseil Général de la Manche. ML was supported by a CIFRE PhD studentship from the Association Nationale de la Recherche et de la Technologie during the course of this study.
Compliance with ethical standards
Conflict of interest
We declare that we have no conflict of interest.
Research involving human participants and/or animals
All applicable international, national and institutional guidelines for the care and use of animals were followed. All procedures performed in studies involving animals were in accordance with the ethical standards of the institution or practice at which the studies were conducted. Biopsy samples were collected under the permit 09/115/DEROG from the French ministry.
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