Slowinski Samuel P, Gresham Jennifer D, Penley McKenna J, Lively Curtis M, Morran Levi T
bioRxiv. 2024 Jan 31:2024.01.30.578011. doi: 10.1101/2024.01.30.578011.
Despite substantial costs, biparental sex is the dominant mode of reproduction across plant and animal taxa. The Red Queen hypothesis (RQH) posits that coevolutionary interactions with parasites can favor biparental sex in hosts, despite the costs. In support of the RQH, previous studies found that coevolutionary interactions with virulent bacterial parasites maintained high outcrossing rates in populations of the androdioecious nematode host . Here we test three non-mutually exclusive mechanisms that could explain how coevolving parasites maintain outcrossing rates in hosts: 1) short-term parasite exposure induces plastic increases in the hosts' propensity to outcross, 2) hosts evolve increased outcrossing propensity in response to selection imposed by coevolving parasites, and 3) outcrossed offspring incur less parasite-mediated fitness loss than selfed offspring, increasing host male frequencies and opportunities for outcrossing. We find no evidence that parasites cause plastic or evolved changes in host outcrossing propensity. However, parental outcrossing significantly increases survival of host offspring in the F2 generation when exposed to a coevolving parasite. Hence, coevolving parasites maintain outcrossing in host populations by selecting against selfed offspring, rather than by inducing changes in the propensity to outcross.
尽管成本高昂，但双亲有性生殖仍是植物和动物类群中主要的繁殖方式。红皇后假说（RQH）认为，尽管存在成本，但与寄生虫的协同进化相互作用可能有利于宿主进行双亲有性生殖。为支持红皇后假说，先前的研究发现，与有毒细菌寄生虫的协同进化相互作用在雄花两性异体线虫宿主种群中维持了较高的异交率。在此，我们测试了三种并非相互排斥的机制，这些机制可以解释协同进化的寄生虫如何在宿主中维持异交率：1）短期接触寄生虫会导致宿主异交倾向的可塑性增加；2）宿主因应协同进化的寄生虫施加的选择而进化出更高的异交倾向；3）杂交后代比自交后代遭受的寄生虫介导的适合度损失更小，从而增加了宿主雄性的频率和异交机会。我们没有发现证据表明寄生虫会导致宿主异交倾向发生可塑性变化或进化性变化。然而，当暴露于协同进化的寄生虫时，双亲异交显著提高了F2代宿主后代的存活率。因此，协同进化的寄生虫通过选择淘汰自交后代，而非通过诱导异交倾向的变化，来维持宿主种群中的异交现象。
