The evolution of complexity: tests of the ecological drivers of eye size evolution in nature

Abstract

Organisms exhibit extensive variation in eye size and structure across the animal kingdom. The long standing hypothesis is that divergent ecological selective pressures drive and maintain this variation. While multiple studies have explored variation in eye size across species, far fewer studies have explored how ecological factors shape the evolution of eye size within species. Additionally, the vast majority of studies to date have evaluated light availability as a key selective force in the evolution of the eye while far fewer studies have addressed the role of alternative ecological selective pressures, such as predation and competition. My dissertation examines (1) how variation in ecological pressures, specifically predation and competition, can drive evolutionary shifts in eye size within species, and (2) the repeatability of these patterns across systems and organisms. First, I explore how ecological factors, including predation, competition, resource availability, and light availability influence the evolution of eye size in natural populations of Trinidadian killifish Rivulus hartii. In my second chapter, I evaluate the fitness correlates of shifts in eye size in killifish from high predation and high competition environments to determine the relationship between eye size, survival, and growth. In my third chapter, I test the mechanistic basis of patterns observed between eye size and growth rate in small scale mesocosm experiments. Finally, I use Daphnia ambigua from lakes in Connecticut that differ in predation intensity to determine the repeatability of ecologically driven shifts in eye size evolution.