Data from: The evolution of sexes: a specific test of the disruptive selection theory

The disruptive selection theory of the evolution of anisogamy posits that the evolution of a larger body or greater organismal complexity selects for a larger zygote, which in turn selects for larger gametes. This may provide the opportunity for one mating type to produce more numerous, small gametes, forcing the other mating type to produce fewer, large gametes. Predictions common to this and related theories have been partially upheld. Here, a prediction specific to the disruptive selection theory is derived from a previously published game-theoretic model that represents the most complete description of the theory. The prediction, that the ratio of macrogamete to microgamete size should be above three for anisogamous species, is supported for the volvocine algae. A fully population genetic implementation of the model, involving mutation, genetic drift and selection, is used to verify the game-theoretic approach, and accurately simulates the evolution of gamete sizes in anisogamous species. This model was extended to include a locus for gamete motility, and shows that oogamy should evolve whenever there is costly motility. The classic two-fold cost of sex may be derived from the fitness functions of these models, showing that this cost is ultimately due to genetic conflict.

异配生殖（anisogamy）演化的歧化选择理论（disruptive selection theory）提出：当生物体体型增大或机体复杂性提升时，自然选择会倾向于形成更大的合子（zygote），而更大的合子又会进一步选择产生更大的配子（gametes）。这一过程或将为某一交配型（mating type）演化出数量更多、体型更小的配子创造条件，进而迫使另一交配型只能产生数量更少、体型更大的配子。该理论与相关理论共通的预测已得到部分验证。本研究基于此前发表的、可完整阐释该理论的博弈论模型（game-theoretic model），推导出歧化选择理论独有的一项预测：异配生殖物种的大配子（macrogamete）与小配子（microgamete）大小比值应大于3，这一预测在团藻藻类（volvocine algae）中得到了支持。我们采用纳入突变、遗传漂变（genetic drift）与自然选择的完整种群遗传学（population genetics）模型实现方案，对该博弈论方法进行了验证，该方案可精准模拟异配生殖物种的配子大小演化过程。我们将该模型拓展至包含配子运动性相关位点的场景，结果表明：只要配子运动过程存在能量代价，卵式生殖（oogamy）就会演化出现。可从上述模型的适应度函数中推导出经典的性双重代价（two-fold cost of sex），研究显示该代价本质上源于遗传冲突（genetic conflict）。