After just nine generations, certain male fruit flies alter their biochemical calling cards to correctly target females within their own species. Similarly, river fish placed in a Washington State lake differentiated according to specific habitats within a mere 13 generations, researchers report 20 October in the international journal, Science.
These findings-described in two separate studies by Australian and U.S. research teams-show that natural selection can help new species emerge much faster than scientists ever imagined.
Instead of geographic features like mountains and rivers, physiological reasons provide the barriers that prevent certain populations of flies and fish from reproducing with other members of their species. The rapid evolution of this situation, called "reproductive isolation," among fish and fruit flies sets the stage for realistic, experimental tests to answer long-standing questions about the role of natural selection in species evolution.
Until now, studies have provided no firm evidence for natural selection's direct role in the evolution of mate recognition systems, the specific mechanisms that males and females of a species use to identify each other. But, research on flies led by Megan Higgie of University of Queensland, Australia, counters this and shows that after nine generations, Drosophila serrata males had increased their mate selectivity by altering their pheromones to improve their chances of actually inseminating a female of their own species. These perfume-like pheromones resembled those of males that already co-existed with a sister species in the wild.
The sole dependence of these flies on pheromones for mate recognition makes them an ideal model organism to study how the frequency of certain characters evolve when faced with a natural selection pressure.
In a second Science study, sockeye salmon adapted to river and lake-beach habitats and evolved partial reproductive isolati
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Contact: Ginger Pinholster
gpinhols@aaas.org
202-326-6421
American Association for the Advancement of Science
19-Oct-2000