Harder Lawrence D, Richards Shane A, Routley Matthew B
Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada.
Evolution. 2008 Jan;62(1):157-72. doi: 10.1111/j.1558-5646.2007.00272.x. Epub 2007 Dec 6.
Hermaphroditism allows considerable scope for contributing genes to subsequent generations through various mixtures of selfed and outcrossed offspring. The fitness consequences of different family compositions determine the evolutionarily stable mating strategy and depend on the interplay of genetic features, the nature of mating, and factors that govern offspring development. This theoretical article considers the relative contributions of these influences and their interacting effects on mating-system evolution, given a fixed genetic load within a population. Strong inbreeding depression after offspring gain independence selects for exclusive outcrossing, regardless of the intensity of predispersal inbreeding depression, unless insufficient mating limits offspring production. The extent to which selfing evolves under weak postdispersal inbreeding depression depends on predispersal inbreeding depression and the opportunity for resource limitation of offspring production. Mixed selfing and outcrossing is an evolutionarily stable strategy (ESS) if selfed zygotes survive poorly, but selfed offspring survive well, and maternal individuals produce enough "extra" eggs that deaths of unviable outcrossed embryos do not impact offspring production (reproductive compensation). Mixed mating can also be an ESS, despite weak lifetime inbreeding depression, if self-mating reduces the number of male gametes available for outcrossing (male-gamete discounting). Reproductive compensation and male-gamete discounting act largely independently on mating-system evolution. ESS mating systems always involve either complete fertilization or fertilization of enough eggs to induce resource competition among embryos, so although reproductive assurance is adaptive with insufficient mating, it is never an ESS. Our results illustrate the theoretical importance of different constraints on offspring production (availability of male gametes, egg production, and maternal resources) for both the course and outcome of mating-system evolution, whereas unequal competition between selfed and outcrossed embryos has limited effect. These results also underscore the significance of heterogeneity in the nature and intensity of inbreeding depression during the life cycle for the evolution of hermaphrodite mating systems.
雌雄同体现象为通过自交和异交后代的各种组合将基因传递给后代提供了相当大的空间。不同家庭组成的适合度后果决定了进化上稳定的交配策略，并取决于遗传特征、交配性质以及控制后代发育的因素之间的相互作用。这篇理论文章考虑了在种群内遗传负荷固定的情况下，这些影响的相对贡献及其对交配系统进化的相互作用效应。后代获得独立后强烈的近亲繁殖衰退会选择排他性异交，无论扩散前近亲繁殖衰退的强度如何，除非交配不足限制了后代的产生。在扩散后较弱的近亲繁殖衰退下自交进化的程度取决于扩散前近亲繁殖衰退以及后代产生资源限制的机会。如果自交合子存活率低，但自交后代存活率高，并且母体个体产生足够的“额外”卵子，使得不可行的异交胚胎死亡不影响后代产生（生殖补偿），那么自交和异交混合是一种进化上稳定的策略（ESS）。尽管终身近亲繁殖衰退较弱，但如果自交减少了可用于异交的雄配子数量（雄配子折扣），混合交配也可以是一种ESS。生殖补偿和雄配子折扣在很大程度上独立作用于交配系统进化。ESS交配系统总是涉及完全受精或使足够数量的卵子受精以引发胚胎间的资源竞争，所以尽管在交配不足时生殖保证是适应性的，但它永远不是一种ESS。我们的结果说明了对后代产生的不同限制（雄配子可用性、卵子产生和母体资源）对于交配系统进化的过程和结果在理论上的重要性，而自交和异交胚胎之间不平等的竞争影响有限。这些结果还强调了生命周期中近亲繁殖衰退的性质和强度的异质性对于雌雄同体交配系统进化的重要性。
