Caves. There’s a whole series of things that tends to happen in creatures that become cave-dwellers. Over and over and over again, animals that live exclusively in caves tend to be blind compared to their closest living relatives.
This makes cave species great for studying evolution, because each cave is a “natural experiment.” Mexican cave fish are a particularly cool case, because we have in the same species both cave dwellers, which are blind, and surface fish, which are not. And they can interbreed.
This new paper looks purely at the genetics of these cave fishes, trying to figure out just how many times they have invaded caves and lost developed the “cave” phenotype. This new paper by Bradic and colleagues is an extensive crunching of gene samples, and concludes that while there were two ancestral populations, those ancestral populations in turn invaded caves several times: a total of five introductions to caves, all told.
Furthermore, although these animals can interbreed in the lab, this seems to be unlikely in nature. Their results indicate low gene flow between the surface population and the cave populations. Still, while low, it’s not zero, suggesting that there is a genuine fitness advantage to the blind cave-dwelling form.
Bradic M, Beerli P, Garcia-de Leon FJ, Esquivel-Bobadilla S, Borowsky RL. 2012. Gene flow and population structure in the Mexican blind cavefish complex (Astyanax mexicanus). BMC Evolutionary Biology 12: 9. DOI: 10.1186/1471-2148-12-9
Photo by Joachim S. Müller on Flickr; used under a Creative Commons license.
Turning light and going blind: A tale of caves and genes