雌性（右）和雄性豆象的交配姿势。

据6月26日的《科学》杂志报道说，对豆象的新的研究使得人们对雌性动物为何不顾时间和能量上的代价而与多个雄性动物交配的某一主要的解释提出了挑战。 瑞典和丹麦的Trine Bilde及其同僚对杂交行为能够帮助雌性动物生出遗传学上更健康的后代的假说进行了的测试。该假说认为，最终能够使雌性卵子受精的精子将来自某个拥有“好的”基因的那个雄性动物。 这种效应可能源自该精子本身在与其它精子的竞争中胜出，或是该雌性动物给予该精子接触卵子的优先权等方法。

研究人员惊奇地发现，当雌性豆象与2个雄性豆象交配的时候，那个“低品质”的雄性豆象的精子会比“高品质”豆象育出更多的后代（用仅交配一次后所产生的后代的数量来衡量）。 这些发现表明，父系对后代的遗传贡献并非是驱使雌性动物杂交的动力。 相反，其解释可能包括“性别拮抗”等位基因之间的对抗。该等位基因对某种性别有益而对另外一种性别则有害。

推荐原始出处：

Science 26 June 2009:DOI: 10.1126/science.1171675

Postmating Sexual Selection Favors Males That Sire Offspring with Low Fitness

Trine Bilde,1,2,* Anne Foged,2 Nadia Schilling,2 G?ran Arnqvist1

Despite the costs of mating, females of most taxa mate with multiple males. Polyandrous females are hypothesized to gain genetic benefits for their offspring, but this assumes paternity bias favoring male genotypes that enhance offspring viability. We determined net male genetic effects on female and offspring fitness in a seed beetle and then tested whether fertilization success was biased in favor of high-quality male genotypes in double mating experiments. Contrary to expectations, high-quality male genotypes consistently had a lower postmating fertilization success in two independent assays. Our results imply that sexually antagonistic adaptations have a major and unappreciated influence on male postmating fertilization success. Such genetic variation renders indirect genetic benefits an unlikely driver of the evolution of polyandry.

1 Department of Ecology and Evolution, Evolutionary Biology Centre, University of Uppsala, Norbyv?gen 18d, SE - 752 36 Uppsala, Sweden.
2 Department of Biological Sciences, University of Aarhus, Ny Munkegade 1540, 8000 Aarhus C, Denmark.