THE EVOLUTION OF COMPLEX TRAITS ACROSS ENVIRONMENTAL GRADIENTS
Understanding the evolution of complex organs is a long-standing goal in evolutionary biology. Complex traits, such as the eye and brain, are frequently presented as examples that challenge our understanding of evolution by natural selection. It is well known that eyes and brains vary tremendously across taxa, and the ongoing assumption has been that observed variation in vertebrate eyes and brains are the result of divergent patterns of ecologically driven selection. Yet, despite much interest, the ecological factors that drive variation in brain and eye size remain unclear. Predator induced mortality has been identified as an ecological selective pressure that shapes the evolution of vertebrate eye size and brain size. This is because increases in eye and brain size can enhance anti-predator responses via improved vision, spatial learning abilities, and overall cognition. My dissertation research has used populations of the Trinidadian killifish, Rivulus hartii, that differ in their exposure to predators to understand how ecological factors can influence selection on, and the evolution of, eyes and brains.
CELLULAR AND PHYSIOLOGICAL PROCESSES UNDERLYING COMPLEX TRAIT VARIATION
While our research on the Rivulus brain has shown that predators can influence the overall brain size of Rivulus, it remains unclear how variation in brain structure, as well as cellular mechanisms, contribute to predator driven shifts in brain size. We are currently collaborating with Kent Dunlap at Trinity College to evaluate how neurogenesis differs between populations of Rivulus that vary in their exposure to predation, as well as how cell proliferation varies across brain structure. Because the life history and environment of Rivulus has been well-studied, this research allows us to understand how these factors contribute to brain growth and neuro-cellular dynamics. We have found that Rivulus from high predation environments have higher rates of neurogenesis than those from sites where predation is weak or absent. These differences in cell proliferation are consistent across brain regions and are maintained in Rivulus in a common garden setting suggesting that these differences have a genetic basis.