Life History Evolution in Guppies: a Model System for the Empirical Study of Adaptation

Abstract

I have used a diversity of observations and experiments to evaluate whether or not guppy life histories represent an adaptation to predator-induced mortality rates. I have primarily worked on natural populations of guppies from Trinidad, but have also considered populations from Tobago and Venezuela. My first step was to compare the life histories of guppies from high and low predation environments. I found that guppies from high predation environments matured more quickly, reproduced more often, and devoted more of their consumed resources to reproduction. They also produced more and smaller offspring in each litter. All of these differences had a genetic basis and many conform to theoretical predictions for how the life history should evolve in response to differences in mortality patterns. I also found that these same patterns were obtained in a new series of localities that had a completely different suite of predators, but had the same contrast between high and low predation communities. I employed mark-recapture techniques to demonstrate that guppies from high predation localities also have significantly higher mortality rates than their counterparts from low predation localities. Such differences in mortality rate provide a potential mechanism for the evolution of these life history patterns. Finally, I have introduced guppies from high predation communities into low predation communities from which they had previously been excluded by waterfalls. These introduced populations evolved in the predicted fashion (delayed maturity, reduced resource allocation to reproduction). Some variables changed significantly in as little as four years, or approximately six generations. While each observation by itself represents an incomplete argument for adaptation, together they make a very strong case for predation and mortality playing a significant role in selecting for interpopulation differences in life histories.