In the few species of birds in which males form display partnerships to attract females, one male secures most or all of the copulations1,2. This leads to the question of why subordinate males help in the absence of observable reproductive benefits. Hamilton's concept of kin selection3, whereby individuals can benefit indirectly by helping a relative, was a crucial breakthrough for understanding apparently altruistic systems. However in the only direct test of kin selection in coordinated display partnerships, partners were unrelated1, discounting kin selection as an explanation for the evolution of cooperation. Here I show, using genetic measures of relatedness and reproductive success, that kin selection can explain the evolution of cooperative courtship in wild turkeys. Subordinate (helper) males do not themselves reproduce, but their indirect fitness as calculated by Hamilton's rule3,4 more than offsets the cost of helping. This result confirms a textbook example of kin selection2 that until now has been controversial5 and also extends recent findings6,7,8 of male relatedness on avian leks by quantifying the kin-selected benefits gained by non-reproducing males.
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I thank E. DuVal, E. Lacey and especially W. Koenig and M. Hauber for comments on the manuscript; J. Dickinson, S. Beissinger, B. Jones, B. Slikas and N. Johnson for training and discussion; B. Davis, A. Hsieh, F. Aguillar, C. Miller, J. Leyhe, R. Orben, L. Robinson, M. Nguyen, B. Loui, M. Nasiri and C. Chu and others for field and laboratory assistance; and P. Kephart for research access to Rana Creek Ranch. My research was funded by an NSF graduate fellowship and dissertation improvement grant, as well as the Animal Behavior Society, American Ornithologists' Union, Sigma Xi, and support from both Integrative Biology and the Museum of Vertebrate Zoology at the University of California, Berkeley.
The author declares that he has no competing financial interests.
This table provides individual histories of coalitions and solitary males. (DOC 34 kb)
This table provides details of the microsatellite loci used, the allelic diversity found in the study population, and the PCR reaction conditions. (DOC 28 kb)
This table details the parameters used in the paternity analysis. (DOC 22 kb)
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