Cameroon lake cichlids probably did not speciate sympatrically: Part 2

Why Evolution Is True

Yesterday I gave the background necessary for understanding a new paper in Evolution by Christopher H. Martin et al. (reference and link below). Today I’ll briefly describe the paper’s findings—findings that cast doubt on one of our premier examples of sympatric speciation.

That example was the existence of assemblages of cichlid fish in small volcanic crater lakes in Cameroon. Because genetic evidence by Schliewen et al. (1994) showed that each assemblage was monophyletic, that is, appeared to descend from a single common ancestral species that invaded the crater lakes some time ago (between 1 and 2.5 myr for Lake Barombi Mbo and 100,000 to 2.5 myr for Lake Bermin), this gave evidence that the formation of 11 species in Barombi Mbo and 9 in Bermin had occurred sympatrically—without geographic isolation of populations.

Read yesterday’s post for background. Here are the two radiations at issue, showing the location of the crater…

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