THE EVOLUTION OF NEUROSENSORY STRUCTURES: EVALUATING ECOLOGICAL DRIVERS OF BRAIN AND EYE SIZE VARIATION

Abstract

Neurosensory structures (i.e., brain and eye size) vary extensively across taxa. The evolution of large neurosensory structures has long been an area of interest for scientists, but focus has largely been placed on macroevolutionary patterns at or above the species level. Few studies have investigated the role contrasting ecological factors play in the evolution of such structures within species. My dissertation examines 1) how divergent ecological pressures, particularly predation and competition, drive evolutionary shifts in brain and eye size within species and across sexes, and 2) why such variation evolves, particularly if larger brains drive shifts in behavior and fitness. First, I further explore known differences in male brain size in Trinidadian killifish (Anablepsoides hartii) to determine if brain structures also evolve across divergent predation regimes and if brain size, brain structure, and eye size co-evolve. In my second chapter, I investigate female brain size and structure to determine if selection operates in a different manner on these traits between sexes and if brain size, structure, and eye size co-evolve in a sex-specific manner. In my third chapter, I evaluate behavioral correlates of increased brain size to determine if jumping behavior in killifish, which is a proxy for fitness, is connected to shifts in brain size and structure. In my fourth chapter, I test for selection on increased brain size and increased fitness by transplanting killifish into novel environments in a transplant mark-recapture experiment. Lastly, I use Daphnia sp. to test the influence of light availability on the evolution of eye size and anti-predator behavior using mesocosm experiments.