Pitnick S, Brown W D, Miller G T
Department of Biology, Syracuse University, NY 13244-1270, USA.
Proc Biol Sci. 2001 Mar 22;268(1467):557-63. doi: 10.1098/rspb.2000.1400.
The relatively small number of ova produced by a female can be fertilized by a single ejaculate in most species. Why females of many species mate with multiple males is therefore enigmatic, especially given that costs associated with remating have been well documented. Recently, it has been argued that females may remate at a maladaptive rate as an outcome of sexually antagonistic coevolution: the evolutionary tug-of-war between manipulation by one sex and resistance to being manipulated by the other sex. We tested this hypothesis experimentally for the evolution of the female remating interval in a naturally promiscuous species, Drosophila melanogaster. In two replicate populations, sexual selection was removed through enforced monogamous mating with random mate assignment, or retained in polyandrous controls. Monogamy constrains the reproductive success of mates to be identical, thereby converting prior conflicts between mates into opportunities for mutualism. Under these experimental conditions, the sexually antagonistic coevolution hypothesis generates explicit predictions regarding the direction of evolutionary change in female remating behaviour. These predictions are contingent upon the mechanism of male manipulation, which may be mediated biochemically by seminal fluids or behaviourally by courtship. Levels of divergence in female remating interval across lines, and in male ejaculatory and courtship effects on female remating, were quantified after 84 generations of selection. Data refute the hypothesis that the evolutionary change in female remating behaviour was due to sexually antagonistic coevolution of courtship signal and receiver traits. The data were, however, consistent with a hypothesis of sexual conflict mediated through ejaculate manipulation. Monogamy-line males evolved ejaculates that were less effective in inducing female non-receptivity and monogamy-line females evolved to remate less frequently, symptomatic of lowered resistance to ejaculate manipulation. The consistency of the results with alternative hypotheses to explain female promiscuity are discussed.
在大多数物种中，雌性产生的卵子数量相对较少，一次射精的精子就可以使这些卵子受精。因此，许多物种的雌性为何会与多个雄性交配是个谜，特别是考虑到再次交配的相关成本已有充分记载。最近，有人认为雌性可能以适应不良的频率再次交配，这是性对抗协同进化的结果：即两性之间在一方操纵与另一方抵制操纵之间的进化拔河。我们通过实验检验了这一假设，该假设涉及自然杂交的黑腹果蝇中雌性再次交配间隔的进化。在两个重复种群中，通过强制一夫一妻制交配并随机分配配偶来消除性选择，或者在一妻多夫制对照组中保留性选择。一夫一妻制限制了配偶的繁殖成功率相同，从而将配偶之间先前的冲突转化为互利共生的机会。在这些实验条件下，性对抗协同进化假设对雌性再次交配行为的进化变化方向产生了明确的预测。这些预测取决于雄性操纵的机制，这可能通过精液进行生化介导，也可能通过求偶行为进行行为介导。在经过84代选择后，对不同品系雌性再次交配间隔的差异程度，以及雄性射精和求偶对雌性再次交配的影响进行了量化。数据驳斥了雌性再次交配行为的进化变化是由于求偶信号和受体性状的性对抗协同进化这一假设。然而，数据与通过射精操纵介导的性冲突假设一致。一夫一妻制品系的雄性进化出的射精在诱导雌性不接受方面效果较差，而一夫一妻制品系的雌性进化为较少再次交配，这表明对射精操纵的抵抗力降低。文中还讨论了这些结果与解释雌性杂交的其他假设的一致性。
