Laboratory of Insect Ecology, Graduate School of Agriculture, Kyoto University, Kitashirakawaoiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan.
Am Nat. 2013 Feb;181(2):223-34. doi: 10.1086/668832. Epub 2013 Jan 14.
The assumption of a twofold cost of sex not only complicates the maintenance of sex but also sets conditions for sexual conflict: in organisms with the twofold cost, males often sexually harass females. Sexual harassment is detrimental to female fitness and thus might help maintain sexual populations if male harassment inflicts a harsher cost on parthenogens than on sexual females (asymmetric harassment cost). However, the generality of this concept is now considered doubtful because selective harassment of parthenogens results in loss of mating opportunities for males. Using three mathematical models, I show here that sexual harassment still can impose the asymmetric cost on parthenogens. First, I apply the Lotka-Volterra model to show the degree of asymmetric harassment cost that permits sex to be maintained stably in the population. Second, using adaptive dynamics, I examine whether sexually antagonistic coevolution for sexual harassment, which occurs only in sexual populations, can promote the asymmetric harassment cost. Finally, an individual-based model, which assumes a spatial structure unlike that in the other two, demonstrates that the asymmetric evolution of harassment cost prevents further invasions of parthenogens from different patches into sexual lineages; these mechanisms may account for allopatric distributions of sexual and parthenogenetic lineages as well as the maintenance of sex.
性的双重代价假设不仅使性的维持变得复杂，而且为性冲突设定了条件：在具有双重代价的生物中，雄性经常骚扰雌性。性骚扰对雌性的适合度有害，因此如果雄性的骚扰对孤雌生殖者造成比有性雌性更严重的代价（不对称骚扰代价），它可能有助于维持有性种群。然而，现在认为这个概念的普遍性是值得怀疑的，因为选择性地骚扰孤雌生殖者会导致雄性失去交配机会。使用三个数学模型，我在这里表明，性骚扰仍然可以对孤雌生殖者施加不对称的代价。首先，我应用洛特卡-沃尔泰拉模型来显示允许性在种群中稳定存在的不对称骚扰代价的程度。其次，使用适应动态，我研究了仅在有性种群中发生的性骚扰的性拮抗共同进化是否可以促进不对称骚扰代价。最后，一个基于个体的模型，它假设了与其他两个模型不同的空间结构，表明骚扰代价的不对称进化可以防止来自不同斑块的孤雌生殖者进一步侵入有性谱系；这些机制可能解释了有性和孤雌生殖谱系的地理分布以及性的维持。
