Rapid Evolution in the Green Anole
Two species of anoles are found in the southeastern U. S., the native green anole (Anolis caroliniensis) and the closely related but non-native brown anole (A. sagrei). The two species interact wherever they co-occur in the U. S. (mainly in Florida), with the brown anole typically outcompeting the green anole in the struggle for space and resources.
Stuart et al investigated the extent of evolutionary divergence of the two species of anoles on islands off the east coast of central Florida. At the study site, A. carolinensis occupied all of the 11 islands studied while A. sagrei established populations on five of the study islands sometime between 1995 and 2010. After experimentally introducing brown anoles in 1995 onto islands that formerly held only green anoles, the scientists found that the green anoles moved to higher perches on shrubs and trees after appearance of the brown anole. In contrast, where only the green anole occurred, they occupied elevations ranging from the ground to the tops of trees. Note that the invaded and non-invaded islands did not differ in environmental characteristics important to anole perching or movement. The most interesting aspect of this study was that A. carolinensis developed larger toe pads with more adhesive scales in association with vertical displacement of chosen perches. The morphological change represented a fixed genetic adaptation that manifested after only 20 generations. These results show that evolutionary change in vertebrates can occur in short time scales particularly if competing species are closely related. Relatively few studies have produced evidence of ongoing evolutionary change in vertebrates as opposed to less complex organisms such as bacteria.
To learn more about interactions between these two anole species, see the post “Anoles: Green and Brown and Spreading” under Invasives, elsewhere on this site.
Stuart, Y. E., T. S. Campbell, P.A. Hohenlohe, R. G. Reynolds, L. J. Revell and J. B. Losos 2014. Rapid evolution of a native species following invasion by a congener. Science 346:463-466.