The influence of environmental stress, reproductive mode, and ploidy variation on life-history trait expression.

Environmental stressors are amongst the most important of all components of evolution because they shape life-history traits, critical traits that guide life cycle and are variable within and across species. One potential mechanism that underlines this variation is environmental stress. In my dissertation, I address how environmental stress (nutrient availability and population density) connects to life-history trait variation and evolution, with a particular focus on ploidy level, reproductive mode, and invasion status. I investigate these questions using Potamopyrgus antipodarum, a powerful and appropriate model because of its unique combination of ploidy- and reproductive mode- polymorphism and its status as a worldwide invasive species. In chapter 2, I explored how phosphorus (P) availability can influence growth and body-P content differentially between ploidy levels and reproductive modes, specifically sexual diploids and asexual triploids. My work revealed higher performance of asexual triploid snails relative to sexual diploid counterparts, suggesting advantages of asexual reproduction and polyploidy outweigh the advantages of sexual reproduction and diploidy. In Chapter 3, I explored the effects of P availability on reproduction among diploids, triploids, and tetraploids; I found novel evidence that dietary-P and maternal-P influences reproductive investment and does so differentially across ploidy levels. In Chapter 4, I explored an inherent connection between biological invasions and intraspecific variation for sensitivity to population density. These results revealed that the growth and reproduction of native but not invasive lineages of P. antipodarum counterparts was found to be sensitive to population density, suggesting that the insensitivity displayed by invasive snails could play a role in invasion success. Altogether, my dissertation illuminates how the interplay between fundamental organismal characteristics and environmental factors can influence the expression and maintenance of variation in life-history traits.