[P115] Thermodynamic and kinetic investigation on the formation of periodic layered structure in Ti-Cu/Zn interface reaction

Extrapair copulations (EPCs) occur widely in socially monogamous birds. How cuckolded males respond to the infidelity of their social mates is still problematic. We addressed this question in the ground tit, Pseudopodoces humilis, in which EPCs occur frequently and successful reproduction relies on biparental care. In solitarily breeding pairs, we calculated the feeding rate of social pairs at polyandrous and monogamous females' nests. Compared with that at monogamous nests, cuckolded males increased their feeding rate whereas polyandrous females reduced theirs. Polyandrous females had larger extrapair partners, although their extrapair young were neither heavier nor had higher heterozygosity than their within-pair young. Extrapair males never provided paternal care for the mixed brood and polyandrous females had no opportunity to forage on the territory of extrapair males. Therefore, the energetic benefit polyandrous females obtained was due to the increased parental care of their social mates. Even losing some share, cuckolded males still gained most of the paternity within the mixed brood. By increasing parental care for the current brood, they could ensure the survival of their own offspring. Thus, we suggest that females place their social male in a cruel bind by creating a larger brood containing some unrelated young: if the social male does not step up provisioning to meet the demands of the larger brood, overcrowding may reduce the survival of his offspring. Polyandrous females maintain the fitness incentive for their social males to provide parental care by limiting the paternity of extrapair males to a minority of the brood.