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.

配子异型（anisogamy）演化的分裂选择（disruptive selection）理论提出：躯体更大或机体复杂性更高的演化过程，会正向选择更大的合子（zygote），而合子增大又会进一步青睐更大的配子（gametes）。这将为某一交配型（mating type）创造条件，使其能够产出数量更多的小型配子，进而迫使另一交配型只能产生数量更少但体型更大的配子。该理论及相关理论共有的部分预测已得到部分验证。
本文从已发表的、对该理论做出最完整阐释的博弈论模型（game-theoretic model）中，推导出一项仅适用于分裂选择理论的专属预测：异型配子物种的大配子（macrogamete）与小配子（microgamete）尺寸比值应大于3，这一结论在团藻目藻类（volvocine algae）中得到了支持。
我们采用涵盖突变（mutation）、遗传漂变（genetic drift）与选择过程的完全种群遗传学（population genetic）模型实现方式，对该博弈论方法进行验证，并准确模拟了异型配子物种的配子尺寸演化历程。
该模型被进一步拓展以纳入配子运动性相关的基因座（locus），结果显示，只要配子运动行为存在适应性成本，卵式生殖（oogamy）便会发生演化。
可从上述模型的适合度函数（fitness functions）中推导出经典的性双重代价（two-fold cost of sex），这表明该代价本质上源于遗传冲突。