Pupfishes (Cyprinodon spp.) exhibit some of the fastest rates of evolution in any organism.
This is according to a study to be published in a forthcoming issue of the journal Evolution, in which Christopher Martin and Peter Wainwright studied 48 of the 55 species of Cyprinodon pupfish.
Pupfish are found in north, central and northern South America from Massachusetts to Venezuela. Most of them are morphologically and ecologically very similar, browsing detritus and algae off of rocks.
However, in two places, pupfishes differ considerably in morphology and ecology: the shallow salty lakes of San Salvador Island in the Bahamas, where one species of pupfish has evolved to eat scales off of other fishes and another has evolved to feed on shelled crustaceans (ostracods) and snails, and the Yucatan peninsula in Mexico, where a third species has evolved to eat other fishes and a fourth has evolved to feed on plankton.
The authors found that the three unusual pupfishes have evolved very rapidly in modifying their jaws to suit their diet, with an explosive rate of evolution as high as 131 times faster than the rate seen in other members of the family Cyprinodontidae. The causes of this explosive evolution in pupfishes are not known, although it is likely that large populations living in isolated environments (hot saline lakes) with few competitors may have something to do with it.
Even so, the authors found that fishes living under very similar conditions (e.g. mosquitofishes of the genus Gambusia), have not undergone such explosive evolution and failed to radiate in the presence of the same ecological opportunity.
For more information, see the paper: Martin, CH and PC Wainwright (2011), Trophic novelty is linked to exceptional rates of morphological diversification in two adaptive radiations of Cyprinodon pupfish. Evolution, 65, doi:10.1111/j.1558-5646.2011.01294.
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