Nonaka Etsuko, Kaitala Veijo
Department of Ecology, Environment, and Plant Science Stockholm University Stockholm Sweden.
Present address: Department of Biological and Environmental Science University of Jyväskylä Jyväskylä Finland.
Ecol Evol. 2020 Oct 14;10(23):13030-13043. doi: 10.1002/ece3.6889. eCollection 2020 Dec.
Many parasitoids have single-locus complementary sex determination (sl-CSD), which produces sterile or inviable males when homozygous at the sex determining locus. A previous study theoretically showed that small populations have elevated risks of extinction due to the positive feedback between inbreeding and small population size, referred to as the diploid male vortex. A few modeling studies have suggested that the diploid male vortex may not be as common because balancing selection at sex determining loci tends to maintain high allelic diversity in spatially structured populations. However, the generality of the conclusion is yet uncertain, as they were drawn either from models developed for particular systems or from a general-purpose competition model. To attest the conclusion, we study several well-studied host-parasitoid models that incorporate functional response specifying the number of attacked hosts given a host density and derive the conditions for a diploid male vortex in a single population. Then, we develop spatially structured individual-based versions of the models to include female behavior, diploid male fertility, and temporal fluctuations. The results show that producing a handful of successful offspring per female parasitoid could enable parasitoid persistence when a typical number of CSD alleles are present. The effect of functional response depends on the levels of fluctuations in host abundance, and inviable or partially fertile diploid males and a small increase in dispersal can alleviate the risk of a diploid male vortex. Our work supports the generality of effective genetic rescue in spatially connected parasitoid populations with sl-CSD. However, under more variable climate, the efficacy of the CSD mechanism may substantially decline.
许多寄生蜂具有单基因座互补性性别决定（sl-CSD），当在性别决定基因座上纯合时会产生不育或无法存活的雄性。先前的一项研究从理论上表明，由于近亲繁殖与小种群规模之间的正反馈（即二倍体雄性漩涡），小种群的灭绝风险会升高。一些建模研究表明，二倍体雄性漩涡可能并不常见，因为性别决定基因座上的平衡选择倾向于在空间结构化种群中维持较高的等位基因多样性。然而，这一结论的普遍性仍不确定，因为它们要么是从针对特定系统开发的模型得出的，要么是从通用竞争模型得出的。为了验证这一结论，我们研究了几个经过充分研究的宿主 - 寄生蜂模型，这些模型纳入了功能反应，该反应根据宿主密度指定被攻击宿主的数量，并推导了单一种群中二倍体雄性漩涡的条件。然后，我们开发了基于个体的空间结构化版本的模型，以纳入雌性行为、二倍体雄性育性和时间波动。结果表明，当存在典型数量的CSD等位基因时，每只雌性寄生蜂产生少量成功后代就能使寄生蜂持续存在。功能反应的影响取决于宿主丰度的波动水平，无法存活或部分可育的二倍体雄性以及扩散的小幅增加可以减轻二倍体雄性漩涡的风险。我们的工作支持了在具有sl-CSD的空间相连寄生蜂种群中有效基因拯救的普遍性。然而，在气候变化更大的情况下，CSD机制的功效可能会大幅下降。
