African rift lake cichlids are among the most famous subjects for the study of evolution. The rift lakes formed recently in geological time, but the cichlids that got in have radiated into a dazzling array of species in short order.
But there are cichlids and other similar recent geological events in the Americas, too, just as interesting!
This research by Elmer and colleagues takes advantage of a lake made by volcanic activity, in Nicaragua. The lake appears to have been formed about 1,800 years ago.
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This crater lake has been colonized by Midas cichlids and a few other fishes. The researchers have done a lot of DNA work here, and based on it, they think the Midas cichlids only got into the lake in the last hundred years or so. This population differs in several respects from the cichlids in the nearest neighbouring lakes.
There are two types of Midas cichlids in this lake: there's a common thin-lipped type (pretty sure this is what's pictured here), and a rarer thick lipped type. This difference in appearance is correlated with diet: the common thin-lipped guys have algae, fish and snails in their stomachs, while the thick-lipped one have arthropods.
Elmer and company argue that this could be a case of incipient speciation here. This is an attractive possibility, given that they seem to have two morphs that have different diets, which could leads to different ecological niches, which could lead to reproductive isolation. While plausible, they could not find any genetic distinction between the nuclear or mitochondrial genes between the two morphs (though they commit the crime of "but it's almost significant" for the mitochondrial DNA).
What needs to happen next? Someone needs to make this lake the focus of a career, and start documenting the populations year in, year out, much like Peter and Rosemary Grant did for the Galapagos finches. There need to be behavioural tests to see if fat-lipped females like fat-lipped males more than thin-lipped ones. There need to be ecological studies to see if these animals are inhabiting different locations in the lake.
If this population truly is this young, we have a great chance to watch speciation happen in front of our eyes.
Elmer, K., Lehtonen, T., Kautt, A., Harrod, C., & Meyer, A. (2010). Rapid sympatric ecological differentiation of crater lake cichlid fishes within historic times BMC Biology, 8 (1) DOI: 10.1186/1741-7007-8-60
Midas cichlid picture by Just Chaos on Flickr. Used under a Creative Commons license.