Data from: The consequences of facultative sex in a prey adapting to predation

A species reproductive mode, along with its associated costs and benefits, can play a significant role in its evolution and survival. Facultative sexuality, being able to reproduce both sexually and asexually, has been deemed evolutionary favourable as the benefits of either mode may be fully realized. In fact, many studies have focused on identifying the benefits of sex and/or the forces selecting for increased rates of sex using facultative sexual species. The costs of either mode however can also have a profound impact on a population’s evolutionary trajectory. Here we used experimental evolution and fitness assays to investigate the consequences of facultative sexuality in prey adapting to predation. Specifically, we compared the adaptive response of algal prey populations exposed to constant rotifer predation and which had alternating cycles of asexual and sexual reproduction where sexual episodes were either facultative (sexual and asexual progeny simultaneously propagated) or obligate (only sexual progeny propagated). We found that prey populations with facultative sexual episodes reached a lower final relative fitness and suffered a greater trade-off in traits under selection, i.e. defense and competitive ability, as compared to prey populations with obligate sexual episodes. Our results suggest that costs associated with sexual reproduction (germination time) and asexual reproduction (selection interference) were amplified in the facultative sexual prey populations, leading to a reduction in the net advantage of sexuality. Additionally, we found evidence that the cost of sex was reduced in the obligate sexual prey populations because increased selection for sex was observed via the spontaneous production of sexual cells. These results show that certain costs associated with facultative sexuality can affect an organism’s evolutionary trajectory.

物种的生殖模式及其伴随的成本与收益，对其演化与存活具有至关重要的作用。兼性有性生殖（Facultative sexuality）指生物可同时进行有性与无性生殖，因其能充分利用两种生殖模式的优势，被认为在演化上更具优势。事实上，诸多研究已围绕兼性有性生殖物种展开，旨在揭示有性生殖的优势，以及推动有性生殖频率提升的选择压力。然而，两种生殖模式各自的成本，同样会对种群的演化路径产生深远影响。本研究通过实验演化与适合度测定实验，探究了兼性有性生殖在猎物应对捕食压力过程中产生的演化后果。具体而言，本研究选取持续暴露于轮虫（rotifer）捕食压力的藻类猎物种群作为研究对象，对比两类种群的适应性响应：两类种群均存在无性与有性生殖的交替循环，但其有性生殖阶段分别为兼性模式（同时繁殖有性与无性子代）与专性模式（仅繁殖有性子代）。研究结果显示，与专性有性生殖阶段的猎物种群相比，兼性有性生殖阶段的猎物种群最终相对适合度更低，且在选择压力下的性状权衡（即防御能力与竞争能力之间的权衡）更为显著。本研究结果表明，兼性有性生殖猎物种群中，与有性生殖相关的成本（萌发时间）与无性生殖相关的成本（选择干扰）被进一步放大，最终导致有性生殖的净优势有所降低。此外，本研究发现专性有性生殖猎物种群的有性生殖成本有所降低，这是因为通过自发产生有性生殖细胞的现象，可观察到对有性生殖的选择压力有所提升。上述结果证实，与兼性有性生殖相关的特定成本，能够对生物体的演化路径产生显著影响。