Why do females mate with multiple males?

与雌性交配的雄性数量在不同的动物物种中有很大的差异。基于一妻多夫制对雌性有利的假设，这种种间变异已经被研究了很长时间。我们利用一个种群中存在多夫制程度遗传变异的物种，研究了一夫一妻制/多夫制的进化。这一特征使得不同程度的一妻多夫制种群之间的杂交成为可能。我们选用赤豆甲虫（Callosobruchus chinensis）。首先，我们研究了一种性别的因素是否可能导致人群中多夫制的不同程度。有三种可能的情况：只有女性有责任，只有男性有责任，两者都有责任。我们还发现，在人群中，一妻多夫制的水平存在遗传变异。人工选择实验显示两性的交配率没有相关反应。这表明两性的交配率没有遗传相关性。一妻多夫制对女性的直接好处并没有显示出来。后代适合度的几个组成部分没有显示一妻多夫制对雌性的间接好处。一妻多夫制水平较高的种群中的雄性比一妻多夫制水平较低的种群中的雄性具有更强的精子竞争能力。一妻多夫制的水平也受到包括一天中的时间和产卵基质在内的条件的影响。

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.