How changes in selective regimes affect trait evolution is an important open biological question. We take advantage of naturally occurring and repeated transitions from sexual to asexual reproduction in a New Zealand freshwater snail species, Potamopyrgus antipodarum, to address how evolution in an asexual content- including the potential for relaxed selection on male-specific traits- influences sperm morphology. The occasional production of male offspring by the otherwise all-female asexual P. antipodarum lineages affords a unique and powerful opportunity to assess the fate of sperm traits in a context where males are exceedingly rare. These comparisons revealed that the sperm produced by "asexual" males are markedly distinct from sexual counterparts. We also found that the asexual male sperm harbored markedly higher phenotypic variation and was much more likely to be morphologically abnormal. Together, these data suggest that transitions to asexual reproduction might be irreversible, at least in part because male function is likely to be compromised. These results are also consistent with a scenario where relaxed selection and/or mutation accumulation in the absence of sex translates into rapid trait degeneration.

中文翻译：

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雌性框架中的雄性表型：无性谱系雄性蜗牛产生的精子退化的证据

选择性机制的变化如何影响性状进化是一个重要的开放生物学问题。我们利用新西兰淡水蜗牛 Potamopyrgus antipodarum 中从有性繁殖到无性繁殖的自然发生和重复过渡，来解决无性内容的进化 - 包括对雄性特定性状的放松选择的可能性 - 影响精子形态。由其他全雌性无性 P. antipodarum 谱系偶尔产生的雄性后代提供了一个独特而有力的机会，可以在雄性极其罕见的情况下评估精子特征的命运。这些比较表明，“无性”雄性产生的精子与有性行为的精子明显不同。我们还发现无性雄性精子具有明显更高的表型变异，并且更有可能出现形态异常。总之，这些数据表明向无性繁殖的转变可能是不可逆转的，至少部分是因为男性功能可能会受到损害。这些结果也与在没有性别的情况下放松选择和/或突变积累转化为快速性状退化的情况一致。