Behavioral and genomic consequences of evolution under skewed sex ratios

Abstract

113 pagesIn this dissertation I combine game theoretic modeling with experimental evolution and next-generation sequencing to address the causes and consequences of male and female sexual interactions. In chapter 1, I use tug-of-war theory to model the evolution of male and female sex roles as a function of anisogamy and sex ratio, and show that individuals can diverge in how they allocate their reproductive effort based on either of these parameters. The model incorporates both within-sex competition and between-sex cooperation to demonstrate that sexual interactions underlie the evolution of sexually dimorphic behaviors. In chapter 2, I perform experimental evolution in the laboratory using a nematode with a short generation time, Caenorhabditis remanei, and test an extension of the hypothesis that disrupting male-female interactions has cascading effects on reproductive behavior and gamete investment. By systematically altering the adult sex ratio of replicate populations over 50 generations, I show that males and females increase their mating effort when exposed to a population with an excess of males, but find no effects on their sperm and egg sizes. Chapter 3 extends this experiment by applying a genomic lens to this organism and exploring the consequences of a skewed sex ratio on populations, along with the potential for repeatable evolution in replicate populations faced with identical environmental conditions. I show that populations with a male-biased sex ratio tend towards higher genomic divergence compared to female-biased populations, and that parallel evolution can arise across experimental populations regardless of sex ratio, with implications for the predictability of evolutionary trajectories at short evolutionary timescales. Furthermore, I identify loci that change in allele frequency in opposite directions in male-biased and female-biased populations and are implicated in male mating behavior, indicating possible genes under sexual conflict in this system