Department of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
Centre of Excellence in Biological Interactions, Department of Biological and Environmental Science, University of Jyväskylä, Jyväskylä, Finland.
Proc Biol Sci. 2018 Jan 31;285(1871). doi: 10.1098/rspb.2017.2176.
The timing of sex in facultatively sexual organisms is critical to fitness, due to the differing demographic consequences of sexual versus asexual reproduction. In addition to the costs of sex itself, an association of sex with the production of dormant life stages also influences the optimal use of sex, especially in environments where resting eggs are essential to survive unfavourable conditions. Here we document population dynamics and the occurrence of sexual reproduction in natural populations of across their growing season. The frequency of sexually reproducing females and males increased with population density and with decreasing asexual clutch sizes. The frequency of sexually reproducing females additionally increased as population growth rates decreased. Consistent with population dynamic models showing that the opportunity cost of sexual reproduction (foregoing contribution to current population growth) diminishes as populations approach carrying capacity, we found that investment in sexual reproduction was highest when asexual population growth was low or negative. Our results support the idea that the timing of sex is linked with periods when the relative cost of sex is reduced due to low potential asexual growth at high population densities. Thus, a combination of ecological and demographic factors affect the optimal timing of sexual reproduction, allowing to balance the necessity of sex against its costs.
在兼性有性生物中，性别的时机对适应性至关重要，因为有性繁殖与无性繁殖的人口统计学后果不同。除了性行为本身的成本外，性行为与休眠生命阶段的产生之间的关联也会影响性行为的最佳利用，尤其是在休眠卵对于在不利条件下生存至关重要的环境中。在这里，我们记录了 across 在其生长季节的自然种群中的种群动态和有性繁殖的发生。有性繁殖的雌性和雄性的频率随着种群密度的增加和无性卵囊大小的减小而增加。有性繁殖的雌性的频率随着种群增长率的降低而增加。与显示有性繁殖的机会成本（放弃对当前种群增长的贡献）随着种群接近承载能力而减少的种群动态模型一致，我们发现当无性种群增长较低或为负时，对有性繁殖的投资最高。我们的研究结果支持这样一种观点，即性别的时机与由于高种群密度下潜在的无性生长较低而导致性成本降低的时期有关。因此，生态和人口因素的组合会影响有性繁殖的最佳时机，使能够平衡对性的必要性与其成本。
