Data from: Effects of polyploidy and reproductive mode on life history trait expression

Ploidy elevation is increasingly recognized as a common and important source of genomic variation. Even so, the consequences and biological significance of polyploidy remain unclear, especially in animals. Here, our goal was to identify potential life history costs and benefits of polyploidy by conducting a large multiyear common garden experiment in Potamopyrgus antipodarum, a New Zealand freshwater snail that is a model system for the study of ploidy variation, sexual reproduction, host–parasite coevolution, and invasion ecology. Sexual diploid and asexual triploid and tetraploid P. antipodarum frequently coexist, allowing for powerful direct comparisons across ploidy levels and reproductive modes. Asexual reproduction and polyploidy are very often associated in animals, allowing us to also use these comparisons to address the maintenance of sex, itself one of the most important unresolved questions in evolutionary biology. Our study revealed that sexual diploid P. antipodarum grow and mature substantially more slowly than their asexual polyploid counterparts. We detected a strong negative correlation between the rate of growth and age at reproductive maturity, suggesting that the relatively early maturation of asexual polyploid P. antipodarum is driven by relatively rapid growth. The absence of evidence for life history differences between triploid and tetraploid asexuals indicates that ploidy elevation is unlikely to underlie the differences in trait values that we detected between sexual and asexual snails. Finally, we found that sexual P. antipodarum did not experience discernable phenotypic variance-related benefits of sex and were more likely to die before achieving reproductive maturity than the asexuals. Taken together, these results suggest that under benign conditions, polyploidy does not impose obvious life history costs in P. antipodarum and that sexual P. antipodarum persist despite substantial life history disadvantages relative to their asexual counterparts.

染色体倍性升高（ploidy elevation）日益被认为是基因组变异的常见且重要来源。尽管如此，多倍体（polyploidy）的生物学效应与进化意义仍未明晰，在动物类群中尤为如此。本研究以新西兰淡水螺Potamopyrgus antipodarum为研究对象——该物种是研究倍性变异、有性生殖、宿主-寄生虫协同进化以及入侵生态学的经典模式系统——通过开展一项为期多年的大型同质园实验，旨在明确多倍体潜在的生活史代价与适应收益。有性生殖的二倍体与无性生殖的三倍体、四倍体P. antipodarum常共存，这使得我们能够对不同倍性水平及生殖模式的个体开展严谨的直接对比。在动物类群中，无性生殖与多倍体往往紧密关联，因此我们也可借助上述对比解析有性生殖的维持机制——这一问题本身是进化生物学中尚未解决的核心难题之一。本研究结果显示，有性二倍体P. antipodarum的生长与成熟速度显著慢于其无性多倍体同类。我们发现生长速率与生殖成熟年龄之间存在显著负相关关系，这表明无性多倍体P. antipodarum较早成熟的特性，是由其较快的生长速率驱动的。无性生殖的三倍体与四倍体个体间未发现生活史性状差异，这说明我们观测到的有性与无性螺类间的性状值差异，并非由染色体倍性升高所致。最后，我们发现有性生殖的P. antipodarum并未展现出与有性生殖相关的可观测表型变异收益，且其在达到生殖成熟前死亡的概率显著高于无性生殖个体。综合来看，本研究结果表明：在适宜环境条件下，多倍体并不会给P. antipodarum带来显著的生活史代价；而有性生殖的P. antipodarum尽管相较于无性生殖同类存在显著的生活史劣势，但仍得以存续。