Data from: Parasitic castration promotes coevolutionary cycling but also imposes a cost on sex

Antagonistic coevolution between hosts and parasites is thought to drive a range of biological phenomena including the maintenance of sexual reproduction. Of particular interest are conditions that produce persistent fluctuations in the frequencies of genes governing host-parasite specificity (coevolutionary cycling), as sex may be more beneficial than asexual reproduction in a constantly changing environment. While many studies have shown that coevolutionary cycling can lead to the maintenance of sex, the effects of ecological feedbacks on the persistence of these fluctuations in gene frequencies are not well understood. Here, we use a simple deterministic model that incorporates ecological feedbacks to explore how parasitic reductions in host fecundity affect the maintenance of coevolutionary cycling. We demonstrate that parasitic castration is inherently destabilizing and may be necessary for coevolutionary cycling to persist indefinitely, but also reduces the likelihood that sexually-reproducing individuals will find a fertile partner, which may select against sex. These findings suggest that castrators can play an important role in shaping host evolution and are likely to be good targets for observing fluctuations in gene frequencies that govern specificity in host-parasite interactions.宿主（host）与寄生物（parasite）间的拮抗共进化（antagonistic coevolution）被认为驱动了诸多生物学现象，其中包括有性生殖的维持。尤其值得关注的是，能够引发调控宿主-寄生物特异性的基因频率发生持续性波动的共进化循环（coevolutionary cycling）——因为在持续变化的环境中，有性生殖或许比无性生殖更具进化优势。尽管已有多项研究证实共进化循环可维持有性生殖，但生态反馈（ecological feedbacks）对这类基因频率波动持续性的影响机制仍未得到充分阐明。本研究采用纳入生态反馈的简单确定性模型，探究寄生物对宿主繁殖力（fecundity）的抑制作用如何影响共进化循环的维持。研究结果表明，寄生去势（parasitic castration）本身具有固有的去稳定化效应，且或许是共进化循环得以永久维持的必要条件；但同时，该效应也会降低有性生殖个体找到可育配偶的概率，进而可能对有性生殖产生选择抑制作用。上述发现提示，寄生去势类生物在塑造宿主进化进程中可发挥关键作用，且有望成为观测宿主-寄生物互作中特异性相关基因频率波动的理想研究靶标。