Department of Mathematics, University of York, York YO10 5DD, UK.
Department of Evolutionary Biology and Environmental Studies, University of Zurich, CH-8057 Zurich, Switzerland.
Cells. 2021 Sep 18;10(9):2467. doi: 10.3390/cells10092467.
Recently, it was pointed out that classic models for the evolution of anisogamy do not take into account the possibility of parthenogenetic reproduction, even though sex is facultative in many relevant taxa (e.g., algae) that harbour both anisogamous and isogamous species. Here, we complement this recent analysis with an approach where we assume that the relationship between progeny size and its survival may differ between parthenogenetically and sexually produced progeny, favouring either the former or the latter. We show that previous findings that parthenogenesis can stabilise isogamy relative to the obligate sex case, extend to our scenarios. We additionally investigate two different ways for one mating type to take over the entire population. First, parthenogenesis can lead to biased sex ratios that are sufficiently extreme that one type can displace the other, leading to de facto asexuality for the remaining type that now lacks partners to fuse with. This process involves positive feedback: microgametes, being numerous, lack opportunities for syngamy, and should they proliferate parthenogenetically, the next generation makes this asexual route even more prominent for microgametes. Second, we consider mutations to strict asexuality in producers of micro- or macrogametes, and show that the prospects of asexual invasion depend strongly on the mating type in which the mutation arises. Perhaps most interestingly, we also find scenarios in which parthenogens have an intrinsic survival advantage yet facultatively sexual isogamous populations are robust to the invasion of asexuals, despite us assuming no genetic benefits of recombination. Here, equal contribution from both mating types to zygotes that are sufficiently well provisioned can outweigh the additional costs associated with syngamy.
最近有人指出，经典的雌雄配子非均等进化模型没有考虑到孤雌生殖的可能性，尽管在许多相关的生物类群（如藻类）中，性是兼性的，同时存在雌雄配子非均等和均等的物种。在这里，我们用一种方法来补充最近的分析，这种方法假设亲代大小与其存活率之间的关系可能在孤雌生殖和有性生殖产生的后代中有所不同，有利于前者或后者。我们表明，以前关于孤雌生殖相对于强制性有性生殖可以稳定均等性的发现，也适用于我们的情景。我们还研究了一种交配型接管整个种群的两种不同方式。首先，孤雌生殖可以导致足够极端的偏性性别比，以至于一种类型可以取代另一种类型，从而使另一种类型实际上成为无性生殖，因为它们缺乏与融合的伴侣。这个过程涉及正反馈：微配子数量众多，缺乏合子形成的机会，如果它们进行孤雌生殖，下一代的微配子会使这种无性途径更加突出。其次，我们考虑了微配子或大配子生产者向严格无性生殖的突变，并表明无性入侵的前景强烈取决于突变发生的交配型。也许最有趣的是，我们还发现了一些情景，在这些情景中，孤雌生殖具有内在的生存优势，但兼性雌雄配子均等的种群对无性生殖的入侵具有很强的抵抗力，尽管我们假设重组没有遗传益处。在这里，足够充分供应的受精卵中来自两种交配型的平等贡献，可以超过与合子形成相关的额外成本。
