Tiny pupfish found in the shallow, salty lakes of Mexico and the Caribbean are experiencing some of the fastest evolution ever seen, changing their features 130 times faster than their fishy relatives. And we don't have the foggiest idea why.

There are 50 distinct species of pupfish found everywhere from New England to Venezuela. According to UC Davis researcher Chris Martin, 46 of these species are more or less identical, and the differences between them are very subtle. But the final four species are something else entirely, and that's where we get to our evolutionary mystery.


All the other pupfish eat detritus and algae off of rocks, but a pupfish species in the saltwater lakes of the Bahamas actually bites off the scales of other fish, while another one of the species there likes to eat tiny snails and clam shrimp. Meanwhile, in Mexico's Yucatan peninsula, one species likes to eat other fish and another eats plankton, although both of these are extinct in the wild and now only survive in laboratories.

These four species have all undergone extensive adaptive changes to their jaws in order to make their new diets work, and Martin's research showed that these changes came out of nowhere, evolutionarily speaking. He calculates that some of these changes happened 130 times faster than the rate of evolution in other pupfish, but it's a mystery why this has happened.

The lake water in which all four species live is hot and salty, and that might represent some key common factor...except lots of other pupfish live in similar conditions, and they don't undergo similar changes. Indeed, other fish found in those lakes show no signs of such fast change, so it's anybody's guess what's going on here. Let's just hope these pupfish don't decide they want to become intelligent...they'll have us conquered by 2015.


Via Evolution. Image by Chris Martin.