LIFE-HISTORY EVOLUTION IN GUPPIES - A MODEL SYSTEM FOR THE EMPIRICAL-STUDY OF ADAPTATION

I have used a diversity of observations and experiments to evaluate wh ether or not guppy life histories represent an adaptation to predator- induced mortality rates. I have primarily worked on natural population s 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 gupp ies from high predation elements matured moro 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 t hese differences had a genetic basis and many conform to theoretical p redictions For how thr life history should evolve in response to diffe rences in mortality patterns. I also found that these same patterns we re obtained in a new series of localities that had a completely differ ent suite of predators, but had the same contrast between high and low predation communities. I employed mark-recapture techniques to demons trate that guppies from high predation localities also have significan tly higher mortality rates than their counterparts from low predation localities. Such differences in mortality rate provide a potential mec hanism for the evolution of these life history patterns. Finally, I ha ve introduced guppies from high predation communities into low predati on communities from which they had previously been excluded by waterfa lls. These introduced populations evolved in the predicted fashion (de layed maturity, reduced resource allocation to reproduction). Some var iables changed significantly in as little as four years, or approximat ely six generations. While each observation by itself represents an in complete argument for adaptation, together they make a very strong cas e for predation and mortality playing a significant role in selecting for interpopulation differences in life histories.