Focusing on guppies, small fresh-water fish biologists have studied for long, the researchers found that guppies living in environments with a large number of predators have adapted to reproduce earlier in life than guppies from low-predation localities. Moreover, when reproduction ceases, guppies from high-predation localities are far older, on average, than guppies from low-predation localities, indicating that high-predation guppies enjoy a long "reproductive period" the time between first and last reproduction.

"In earlier work, we showed that guppies from high predation environments have longer lifespans," said David Reznick, professor of biology. "Our new study explores how and why this happens. We found that fish from populations enjoying longer lifespans live longer because there is a selective increase in their reproductive lifespan. Indeed, theory predicts this result because only reproductive lifespan determines fitness."

Study results appear Dec. 27 in the online edition of the Public Library of Science Biology.

The study supports the controversial hypothesis that natural selection the process in nature by which only organisms best adapted to their environment tend to survive and pass on their genetic characters in increasing numbers to succeeding generations introduces changes in only a specific segment of an organism's lifespan.

The researchers conducted their experiments by comparing life-history traits in 240 guppies they retrieved from high- and low-predation streams in mountains in Trin
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Contact: Iqbal Pittalwala
iqbal@ucr.edu
951-827-6050
University of California - Riverside
26-Dec-2005