LTREB: Ecology and Evolution of Cooperative Breeding

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LTREB: Ecology and evolution of cooperative breedingPI: Walter D. Koenig The acorn woodpecker (Melanerpes formicivorus) is a common bird in California that exhibits some of the most complex social behavior of any vertebrate. Group composition consists of anything from a simple breeding pair to groups containing up to 7 males sharing breeding status (cobreeders), 3 females laying eggs in the same nest cavity (joint-nesters), and a variable number of nonbreeding helpers that are offspring of the breeders from prior years. Prior work has revealed that up to 3 males and 3 females may contribute genetically to a single nest. The degree to which one of these individuals monopolizes parentage within a group, known as "reproductive skew", is low among joint-nesting females but high among cobreeder males. That is, within a nest, one male usually sires all or nearly all the young. This high degree of reproductive skew among cobreeder males is predicted by current theory given the apparent advantages to living in groups and the difficulty of leaving a group and going off on one's own. By comparing paternity in first and second nests of groups with 2 cobreeder males, the proposal will test the alternative hypothesis that cobreeder males have equal chance of siring young, but that paternity of individual young within a brood is an "all or none" phenomenon rather than independently determined for each nestling. If so, this would imply that females, rather than one of the cobreeder males, are in control of paternity, counter to a major assumption of reproductive skew theory. The proposal will also extend prior results by examining behavior and paternity in groups containing 3 or more cobreeder males and in groups with both cobreeder males and joint-nesting females.