In the 1950s, Peter Medawar, winner of a Nobel Prize for medicine, and George Williams, a renowned evolutionary biologist, developed theories for the evolution of senescence, which predicted that organisms that are exposed to high mortality imposed by external factors, like disease or predation, will evolve to deteriorate more rapidly as they get older. Their predictions have been widely accepted and are supported by some experiments. Now, a study by UC Riverside researchers comparing fish living in high- and low-predator environments has found that these classically held theories of aging fail to predict how aging has evolved in nature.

The research findings of David Reznick, a professor of biology at UCR, were published in an article titled "Effects of Extrinsic Mortality on the Evolution of Senescence in Guppies" in the Oct. 28 issue of Nature. Co-authors included UCR colleagues Michael J. Bryant and Derek Roff; and from Colorado State University, biologists Cameron K. and Dionna E. Ghalambor.

The research group studied 240 individually reared guppies, derived from four natural populations. The grandparents of these fish were collected from two watersheds in the Caribbean island of Trinidad. Each watershed held populations that lived either with or without predators and hence experienced either high or low mortality rates. The researchers evaluated aging in these fish by comparing their life spans, mortality rates, fertility, and their swimming performance. Some of their results were not predicted by theory.

"We instead found that senescence was a mosaic of traits," said Reznick. "The high-predation guppies have longer average and maximum lifespans. They have lower mortality rates throughout their lives. They
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Contact: Ricardo Duran
ricardo.duran@ucr.edu
951-827-5893
University of California - Riverside
8-Nov-2004