Genomic determination of reproductive mode in facultatively parthenogenetic Opiliones

Sexual reproduction may pose myriad short-term costs to females. Despite these costs, sexual reproduction is near ubiquitous. Facultative parthenogenesis is theorized to mitigate some of the costs of sex, as individuals can participate in occasional sex to limit costs while obtaining many benefits. However, most theoretical models assume sexual reproduction is fixed following mating, with no possibility of clutches of mixed reproductive ontogeny. Therefore, we asked: if coercive males are present at high frequency in a population of facultative parthenogens, will their clutches be solely sexually produced, or will there be evidence of sexually and asexually-produced offspring? How will their offspring production compare to conspecifics in low frequency male populations? We addressed our questions by collecting females and egg clutches of the facultatively parthenogenetic Opiliones species Leiobunum manubriatum and L. globosum. In L. manubriatum, females from populations with few males were not significantly more fecund than females from populations with higher male relative frequency, despite the potential release of the former from sexual conflict. We used three genotyping methods along with a custom set of DNA capture probes to reveal that offspring of L. manubriatum from these high male populations were primarily produced via asexual reproduction. This is surprising because sex ratios in these southern populations approach equality, increasing the probability for females to encounter mates and produce offspring sexually. We additionally found evidence for reproductive polymorphisms within populations. Rapid and accurate SNP genotyping data will continue to allow us to address broader evolutionary questions regarding the role of facultative reproductive modes in the maintenance of sex.

有性生殖可能会给雌性带来诸多短期代价。尽管存在这些代价，有性生殖仍几乎遍布所有生物类群。兼性孤雌生殖（facultative parthenogenesis）理论上可缓解有性生殖的部分代价，因为个体可通过偶尔进行有性生殖来控制成本，同时获取诸多收益。不过，绝大多数理论模型均假定交配后有性生殖模式固定，无法产生兼具两种生殖发育方式后代的卵块。因此，本研究提出如下问题：若在兼性孤雌生殖种群中，胁迫性雄性的出现频率较高，雌性所产卵块是否仅通过有性生殖产生？抑或会同时存在有性生殖与无性生殖产生的后代？该种群雌性的后代产出情况，与雄性频率较低种群中的同种个体相比，又会有何差异？
本研究通过采集兼性孤雌生殖的盲蛛目（Opiliones）物种Leiobunum manubriatum及L. globosum的雌性个体与卵块，对上述问题展开探究。针对Leiobunum manubriatum，尽管雄性稀少的种群中的雌性理论上可摆脱性冲突的束缚，但其繁殖力并未显著高于雄性相对频率较高的种群中的雌性。本研究采用三种基因分型方法，结合定制化DNA捕获探针，结果显示：来自高雄性频率种群的Leiobunum manubriatum后代主要通过无性生殖产生。这一结果令人意外，因为这些南部种群的性比接近1:1，雌性遭遇雄性并通过有性生殖产生后代的概率本应更高。此外，本研究还发现种群内存在生殖多态性的证据。快速且精准的单核苷酸多态性（SNP）基因分型数据，将持续助力我们解答更广泛的演化问题，即兼性生殖模式在维持有性生殖过程中所发挥的作用。