Periodic, parasite-mediated selection for and against sex

Asexual lineages should rapidly replace sexual populations. Why sex then? The Red Queen hypothesis proposes that parasite-mediated selection against common host genotypes could counteract the per-capita birth rate advantage of asexuals. Under the Red Queen, fluctuations in parasite-mediated selection can drive fluctuations in the asexual population, leading to the coexistence of sexual and asexual reproduction. Does shifting selection by parasites drive fluctuations in the fitness and frequency of asexuals in nature? Combining long-term field data with mesocosm experiments, we detected a shift in the direction of parasite selection in the snail Potamopyrgus antipodarum and its coevolving parasite Microphallus sp. In the early 2000's, asexuals were more infected than sexuals. A decade later, the asexuals had declined in frequency and were less infected than sexuals. Over time, the mean infection prevalence of asexuals equaled that of sexuals, but varied far more. This variation in as...

无性系谱系应迅速取代有性种群。那么性为何存在？红皇后假说（Red Queen hypothesis）提出，寄生虫介导的针对常见宿主基因型的选择，可抵消无性生物在人均出生率上的优势。在红皇后假说框架下，寄生虫介导的选择波动可驱动无性种群的波动，进而促成有性繁殖与无性繁殖的共存。自然界中，寄生虫选择方向的转变是否会驱动无性生物适合度与频率的波动？结合长期野外数据与中宇宙实验（mesocosm experiments），我们在螺类Potamopyrgus antipodarum及其协同进化的寄生虫Microphallus sp.中检测到寄生虫选择方向的转变。2000年代初期，无性螺的感染率高于有性螺；十年后，无性螺的频率下降，且感染率低于有性螺。随着时间推移，无性螺的平均感染率（infection prevalence）与有性螺持平，但波动幅度显著更大。这种无性生物的变异...