Effects of polyploidy and reproductive mode on life history trait expression

Abstract

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.

Impacts of Nitrogen and Phosphorus: From Genomes to Natural Ecosystems and Agriculture

“…A stoichiometric perspective leads us to speculate that genome size and ploidal level are important but often ignored functional traits. For example, very large genomes in plants could be selected against in many ecosystems due to their higher demands for N and P. In animals, there may also be selection against larger genomes due to the reduced fitness associated with relatively low developmental rates and the relatively high demand for P invested in RNA (as much as 50-80% of cellular P) for protein synthesis (Hessen and Persson, 2009;Neiman et al, 2013a, but see Larkin et al, 2016). A definitive answer to the question of the extent to which larger genome sizes and higher ploidal levels translate into N and P costs will require characterization of organismlevel consequences.…”

Parasite resistance predicts fitness better than fecundity in a natural population of the freshwater snailPotamopyrgus antipodarum

“…Females brood their offspring and give birth to crawl-away juveniles. In laboratory conditions, the snails reach maturity in 4-12 months (Winterbourn 1970;Larkin et al 2016). In natural populations, juveniles born in the spring may reach maturity in late summer, and before the next summer season, if born later in the season.…”

Embryonic ontogeny of three species of Horned Frogs, with a review of early development in Ceratophryidae

“…Polyploidy is an important evolutionary phenomenon that causes the wholegenome multiplication and a consequent genomic redundancy. Both higher and lower growth rates are expected in polyploid species, based on a positive correlation with the major RNA content, and a slower metabolic rate and longer cell cycle duration, respectively (Larkin, Tucci, & Neiman, 2016;Otto, 2007). In a large-scale study of evolution of genome size in amphibians, Liedtke, Gower, Wilkinson, and Gomez-Mestre (2018) found that more rapid growth rates are associated with smaller genomes.…”