Wednesday, June 3, 2009

The Pace of Evolution

A recent study of guppy adaptation has shed light on the rapidity of evolutionary change. Over the course of a few years, a population of guppies evolved quantifiable phenotypic changes with consequences for individual fitness and population dynamics. In the face of fast environmental change, the species that is able to adapt most quickly will thrive.

A research team at the University of California examined 200 guppies from Yarra River in Trinidad and introduced them into the previously guppy-free Damier environment. Some guppies were placed in an environment with no predators, while other guppies were placed in an environment with predators.

A mere 8 years after their introduction, the team found that “the females had altered their reproductive effort to match their surroundings.” Where there were predators, the females had altered their reproductive cycle to produce more embryos, thus increasing the chance that some would survive in a hostile environment. Where there were no embryos, the females had altered their reproductive cycle to produce fewer embryos, thus “expending fewer resources on reproduction.” (This latter adaptation coincides with the energetic definition of fitness, which emphasizes a maximal distribution of energy among food acquisition, metabolism, growth, reproduction, and survival.)

To test whether or not these adaptations conferred greater survival advantages, scientists introduced new Yarra guppies into the Damier environment. The guppies that had been there for 8 years were found to have a “significant survival advantage over the more recently introduced group.” In fact, the evolved guppies had a 54-59% increased survival rate over the un-evolved group after 13-26 generations.

These results correspond to earlier laboratory research on this subject, which has shown a promising increase in fitness of 1-10% per generation. The researchers noted, “The changes in survival in our study may initially seem encouraging from a conservation perspective, [but] it is important to remember that the elapsed time frame was 13-26 guppy generations. The current results may therefore provide little solace for biologists and managers concerned with longer-lived species.” Nevertheless, the research suggests that the bulk of the adaptive change occurred early on in an asymptotic fashion. More fine-tuned analysis is needed in order to disaggregate the effects of time and phenotypic change on individual fitness and population persistence.

For a brief synopsis of this study, see Science News.
For the official scientific publication of this study, see the American Naturalist.

-Alyssa Martin

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