Hybrid inviability did not drive cichlid speciation

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Hybrid inviability is not likely to have led to speciation or to maintain species boundaries in some Lake Victoria cichlids, according to recent research.

The research is published in the most recent issue of the Journal of Evolutionary Biology by Inke van der Sluijs, Tom van Dooren, Ole Seehausen and Jacques van Alphen.

The authors studied the closely related sibling species Pundamilia nyereri and P. pundamilia, carrying out reciprocal crosses between the two species.

The authors also crossed the hybrid offspring with individuals of both parent species.

The authors measured fecundity (number of eggs per clutch), fertility (proportion of eggs fertilized among the total number of eggs), egg size, survival rate, growth rate and the sex ratio of all the experimental crosses performed.

Although genic hybrid incompatibilities have been found in many pairs of sister species of fishes (e.g. in sticklebacks and darters), the authors found no such incompatibilities in the hybrids of the experimental crosses, i.e. the hybrids suffered no intrinsic fitness reduction relative to nonhybrids.

The authors surmise that this may be due to the very young age of the species being studied (most speciation in the Lake Victoria cichlids is likely to have occurred within the past 16,500 years), although examples of species that have developed intrinsic incompatibilities in an unexpectedly short time also exist.

According to the authors, ur data suggest that the evolution of divergent mating preferences and speciation in Pundamilia may not have been driven by selection for avoidance of genic incompatibilities. As a corollary, this makes it more likely that speciation was driven directly by environment-dependent sexual and ecological selection.

For more information, see the paper: van der Sluijs, I, TJM van Dooren, O Seehausen and JJM van Alphen (2008) A test of fitness consequences of hybridization in sibling species of Lake Victoria cichlid fish. Journal of Evolutionary Biology 21, pp. 480"491.