Andersson Malte
Department of Zoology, University of Gothenburg, Box 463, SE 405 30 Göteborg, Sweden.
Evolution. 2004 Jan;58(1):24-34. doi: 10.1111/j.0014-3820.2004.tb01570.x.
Sexual selection in the form of sperm competition is a major explanation for small size of male gametes. Can sexual selection in polyandrous species with reversed sex roles also lead to reduced female gamete size? Comparative studies show that egg size in birds tends to decrease as a lineage evolves social polyandry. Here, a quantitative genetic model predicts that female scrambles over mates lead to evolution of reduced female gamete size. Increased female mating success drives the evolution of smaller eggs, which take less time to produce, until balanced by lowered offspring survival. Mean egg size is usually reduced and polyandry increased by increasing sex ratio (male bias) and maximum possible number of mates. Polyandry also increases with the asynchrony (variance) in female breeding start. Opportunity for sexual selection increases with the maximum number of mates but decreases with increasing sex ratio. It is well known that parental investment can affect sexual selection. The model suggests that the influence is mutual: owing to a coevolutionary feedback loop, sexual selection in females also shapes initial parental investment by reducing egg size. Feedback between sexual selection and parental investment may be common.
以精子竞争形式存在的性选择是雄配子体积较小的主要原因。在具有性别角色反转的多配偶制物种中，性选择是否也会导致雌配子体积减小呢？比较研究表明，随着一个谱系进化出社会性多配偶制，鸟类的卵大小往往会减小。在此，一个数量遗传模型预测，雌性对配偶的争夺会导致雌配子体积减小。雌性交配成功率的提高推动了更小的卵的进化，因为产生更小的卵所需时间更少，直到后代存活率降低达到平衡。通常通过增加性别比（雄性偏多）和最大可能配偶数量，平均卵大小会减小，多配偶制会增加。多配偶制也会随着雌性开始繁殖的异步性（方差）增加。性选择的机会随着最大配偶数量增加，但随着性别比增加而减少。众所周知，亲代投资会影响性选择。该模型表明这种影响是相互的：由于存在共同进化的反馈回路，雌性中的性选择也会通过减小卵大小来塑造初始亲代投资。性选择和亲代投资之间的反馈可能很常见。
