Molecular Markers and the Speciation of African Cichlid Fish

Abstract

The cichlid fish of the African Great Lakes represent an astounding example of explosive speciation and adaptive radiation. The rapid nature of the evolution of these species has provoked intense interest in the evolutionary mechanisms responsible for causing and maintaining divergence in this remarkable group of organisms.

The sexual dichromatism and breeding behaviour exhibited by some groups of African cichlids have led many researchers to infer that sexual selection through female preference for male colour patterns may be one such mechanism. Given the apparent importance of male colour patterns in mate choice, the specific status of allopatric populations that vary in male colour patterns is unclear. Microsatellite DNA was used to assess the paternity of offspring in two sets of mate choice trials where females chose between males that differ in colour pattern. One trial tested a sympatric species pair from Lake Victoria (Pundamilia pundamilia and P. nyererei), and the other tested two allopatric populations of the same putative species from Lake Malawi (Metriaclima zebra). In both cases, non-assortative mating was observed. However it was not clear if these results indicated genuine female choice or were a product of the design of the trials. Microsatellite DNA can also be used to generate statistical estimates of pairwise relatedness. The effect on such estimates of locus number and heterozygosity was assessed in two species of cichlids from Lake Malawi (M. zebra and M. callainos). A total of eleven loci were used in a combination of tests on known relatives and computer simulations. It was found that using a higher number of more variable loci resulted in more accurate estimates of relatedness. However it was observed that nine loci provided a similar degree of accuracy to that obtained using eleven loci. This result has obvious implications for the time and cost required for large-scale studies of relatedness in natural populations. Phylogenetic relationships between populations and species of rock-dwelling cichlids from Lake Malawi were reconstructed using both six microsatellite loci and AFLP markers.

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