Rapid evolution of sex frequency and dormancy as hydroperiod adaptations

Dormancy can serve as an adaptation to persist in variable habitats, and often is coupled with sex. In cyclically parthenogenetic rotifers an asexual phase enables rapid population growth, whereas sex results in diapausing embryos capable of tolerating desiccation. Few studies have experimentally tested whether sex-dormancy associations in temporary waters reflect evolution in response to the short hydroperiod selecting for diapause ability. Here we demonstrate evolution of higher propensity for sex and dormancy in ephemeral rotifer cultures mimicking temporary ponds, and lower propensity in permanent cultures. Results are consistent with rapid evolution, with evolutionary changes occurring in a short timeframe (385 d, ≤84 generations). We also provide insight into mechanisms for rapid evolution in basal metazoans, discussing potential roles of new mutations, recombination, and clonal selection.休眠可作为生物在多变生境中存续的适应性策略，且常与有性生殖耦合发生。对于周期性孤雌生殖轮虫 (cyclically parthenogenetic rotifers) 而言，无性生殖阶段可实现种群的快速增长，而有性生殖则能产生可耐受脱水的滞育胚胎 (diapausing embryos)。目前鲜有研究通过实验验证，临时水域中的有性生殖-休眠关联是否反映了针对筛选滞育能力的短水文周期 (hydroperiod) 所产生的适应性演化。本研究证实，在模拟临时池塘的短期轮虫培养体系 (ephemeral rotifer cultures) 中，轮虫的有性生殖与休眠倾向显著升高，而在永久培养体系中该倾向则显著降低。研究结果符合快速演化的理论预期，演化变化可在较短时间尺度（385天，≤84代）内完成。本研究还为基础后生动物 (basal metazoans) 的快速演化机制提供了新见解，探讨了新突变、重组以及克隆选择在其中的潜在作用。