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Experimental studies of evolution in natural populations of guppies

David Reznick, Ph.D.
University of California, Riverside

Wednesday, October 18, 2000
3:00 p.m.—Pacific Forum

People commonly think of evolution as an unobservably slow, continuous process that can cause large changes if it persists for a long time. Our common examples of evolution by natural selection usually involve anthropogenic changes in the environment, such as industrial melanism in moths, insecticide resistance in mosquitoes, or heavy metal tolerance in plants. While these examples show that the process can work in nature, they may not be representative of normal events because of unusually strong coefficients of selection.

My research involves testing the predictions of evolution theories in natural populations. These predictions can be experimentally evaluated and the rate of evolution that we see is four to seven orders of magnitude faster than rates that are inferred from the fossil record. I work on the evolution of life history patterns and evaluate theories that predict how the life history should evolve in response to changes in mortality rate. The "life history" consists of variables that contribute directly to propagation, including the age and maturity, number of offspring per litter, allocation of resources to offspring, and frequency of reproduction.

Theory predicted that high adult mortality rates favor individuals that mature at an earlier age and devote more of their resources to reproduction. I tested these predictions in populations of guppies in high or low predation environments from the Northern Range Mountains of Trinidad. As predicted by theory, guppies from high predation environments attain maturity at an earlier age and smaller size than their counterparts from low predation environments. In addition, they devote more of their consumed resources to reproduction than their counterparts from low predation localities. These differences have a genetic basis, and neutral genetic markers indicate that these patterns have evolved independently in different river drainages. The causal role of perdition and mortality rates in selecting for these life history differences was tested with replicated introduction experiments. These experiments revealed rapid evolution in response to a change in perdition that is consistent with theoretical predictions. They also make it possible to characterize the process of natural selection and evolution.

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