Fuller Evolutionary Biology Program, Cornell Lab of Ornithology, Cornell University, Ithaca, New York 14850, USA.
Am Nat. 2010 Jan;175(1):E1-9. doi: 10.1086/648553.
The idea that extrapair paternity (EPP) in birds is part of a mixed reproductive strategy driven primarily by females is controversial. In cooperatively breeding American crows, we compared predictions of four female benefits hypotheses-the genetic diversity, good genes, genetic compatibility, and direct benefits hypotheses-to our predictions if EPP was primarily male driven. We found that genetically diverse broods were not more successful, extrapair young were not in better condition and did not have a higher survival probability, and, contrary to prediction, offspring sired by within-group extrapair males were more inbred than within-pair offspring. There was evidence of direct benefits, however: provisioning rate and number of surviving offspring were higher in groups containing within-group extrapair sires. Females therefore derived no apparent benefits from extragroup extrapair males but both direct benefits and genetic costs from within-group extrapair males. We suggest that males and females both influence the distribution of EPP in this system.
鸟类中外亲交配（EPP）是由雌性主导的混合繁殖策略的一部分，这种观点颇具争议。在合作繁殖的美洲乌鸦中，我们比较了四种雌性利益假说——遗传多样性、优良基因、遗传相容性和直接利益假说——的预测结果，如果 EPP 主要由雄性驱动，我们的预测结果会怎样。我们发现，遗传多样性丰富的雏鸟并没有更成功，外亲子代的状况也没有更好，生存概率也没有更高，而且与预测相反，来自群体内的外亲子代的后代比同群内的后代更近交。然而，有直接利益的证据：包含群体内外亲子代的群体的喂养率和存活后代的数量更高。因此，雌性从外群外亲子代雄性中没有获得明显的利益，但从同群内的外亲子代雄性中获得了直接利益和遗传代价。我们认为，在这个系统中，雄性和雌性都影响着 EPP 的分布。
