Why do females mate with multiple males?

雌性交配的雄性数量在不同的动物种类中表现出很大的差异。这种种间变异已经被研究了很长时间，基于一夫多妻给女性带来好处的假设。我们利用一个种群间具有一夫多妻程度遗传变异的物种来研究一夫一妻/一夫多妻的进化。这一特征使得具有不同水平的多妻制的种群之间的杂交成为可能。我们用的是小豆甲虫(Callosobruchus Chinensis)。首先，我们考察了一种性别因素导致人群中不同程度的一夫多妻制的可能性。有三种可能的情况：只有女性负责，只有男性负责，两者都有责任。我们还发现，群体间的一夫多妻制水平存在遗传差异。人工选择实验表明，两性的交配率没有相关性。这表明雌雄交配率之间没有遗传相关性。一夫多妻制对女性的直接好处并未显示出来。后代健康的几个组成部分并没有显示出一夫多妻制对女性的间接好处。一夫多妻制水平较高的人群中的男性比一夫多妻制水平较低的人群中的男性表现出更大的精子竞争能力。一夫多妻制的程度也受到条件的影响，包括一天中的时间和产卵的底物。

The number of males which a female mates with shows a large variation among animal species. This interspecific variation has been studied for a long time, based on hypotheses that invoke benefits of polyandry for females. We studied the evolution of monogamy/polyandry by using a species that has the genetic variation of the degree of polyandry among populations. This feature makes the crossing among populations with different levels of polyandry possible. We used the adzuki bean beetle (Callosobruchus chinensis). First, we examined the possibility that factors in one sex is responsible for the different levels of polyandry among populations. There were three possible case : only females are responsible, only males are responsible, and both are responsible. We also showed that there was a genetic variation of levels of polyandry among populations. Artificial selection experiments showed no correlated response in the rates of mating in two sexes. This suggested that the no genetic correlation in the rates of mating of two sexes. The direct benefit of polyandry for females was not shown. Several components of offspring fitness did not show the indirect benefit of polyandry for females. Males in the population with a higher level of polyandry showed a larger ability of sperm competition over males of the population with a lower level of polyandry. The level of polyandry was also affected by conditions including the time in a day and substrate for oviposition.