Male phenotypes in a female framework: Evidence for degeneration in sperm produced by male snails from asexual lineages

• Published in: Journal of evolutionary biology Vol. 33; no. 8; pp. 1050 - 1059
• Main Authors: Jalinsky, Joseph, Logsdon, John M., Neiman, Maurine
• Format: Journal Article
• Language: English
• Published: Switzerland Blackwell Publishing Ltd 01-08-2020
• Subjects: Asexual reproduction; Asexuality; Biological evolution; Context; Degeneration; evolution of sex; Males; Morphology; Mutation; mutation accumulation; Offspring; Phenotypes; Phenotypic variations; Potamopyrgus antipodarum; relaxed selection; Reproduction; Reproduction (biology); sexual reproduction; Snails; Sperm; relaxed selection; mutation accumulation; Potamopyrgus antipodarum; sexual reproduction; sperm; males; asexual reproduction; evolution of sex
• ISSN: 1010-061X; 1420-9101
• DOI: 10.1111/jeb.13632

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 context—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 harboured 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.
We compare sperm morphology from sexual and asexual Potamopyrgus antipodarum, a New Zealand freshwater snail that is comprised of coexisting and ecologically similar sexual and asexual lineages. We leverage the rare occurrence of asexually‐produced males to assess the fate of sperm traits that have been genomically carried in an all‐female background. We find that the sperm of sexual and asexually‐produced males are qualitatively different from each other across several evolutionarily independent sex‐to‐asex transitions.