Kin selection in Columbian ground squirrels: direct and indirect fitness benefits

Authors

  • F. STEPHEN DOBSON,

    1. Centre d’Ecologie Fonctionnelle et Evolutive, Groupe d’Ecologie Comportementale, UMR 5175 CNRS, 1919 Route de Mende, 34293 Montpellier Cedex 05, France
    2. Department of Biological Sciences, Auburn University, 311 Funchess Hall, Auburn, AL 36849, USA
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  • VINCENT A. VIBLANC,

    1. Département d’Ecologie, Physiologie et Ethologie, IPHC, UMR 7178 CNRS, 23 rue Becquerel, 67087 Strasbourg Cedex 02, France
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  • COLINE M. ARNAUD,

    1. Centre d’Ecologie Fonctionnelle et Evolutive, Groupe d’Ecologie Comportementale, UMR 5175 CNRS, 1919 Route de Mende, 34293 Montpellier Cedex 05, France
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  • JAN O. MURIE

    1. Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada
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F. Stephen Dobson, Fax: +33 (0) 4 67 41 21 38; E-mail: fsdobson@msn.com

Abstract

Empirical and theoretical studies have supported kin selection by demonstrating nepotism or modelling its conditions and consequences. As an alternative, we previously found that female Columbian ground squirrels had greater direct fitness when more close kin were present. Extending those results, we used population matrix methods to calculate minimum estimates of individual fitness, estimated direct and indirect components of fitness, estimated inclusive fitness by adding the direct fitness (stripped of estimated influences of the social environment) and indirect fitness components together, and finally looked for inclusive fitness benefits of associations with close kin who seem to be ‘genial neighbours’. We examined the estimated fitness of a sample of 35 females for which complete lifetimes were known for themselves, their mothers and their littermate sisters. Six of these females had no cosurviving adult close kin, and their direct fitness was significantly lower than 29 females with such kin (λ = 0.66 vs. λ = 1.23). The net fitness benefit of the presence of close kin was thus 0.57. The estimated indirect component of fitness through benefits to the direct fitness of close kin was 0.43. Thus, estimated inclusive fitness for females with cosurviving close kin (λ = 1.09) was significantly greater than that for females without surviving close kin (viz., λ = 0.66). The presence of closely related and philopatric female kin appeared to result in considerable fitness benefits for female ground squirrels, perhaps through the behavioural mechanisms of lowered aggression and other forms of behavioural cooperation.

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