The Cichlid Fishes of Lake Malawi, Africa

Abstract of Publication

Moran, P., and I. Kornfield. 1995. Were population bottlenecks associated with the radiation of the mbuna species flock (Teleostei: Cichlidae) in Lake Malawi? Molecular Biology and Evolution 12 (6): 1085-1093.  

Mitochondrial DNA haplotype diversity and frequency distribution were examined within and among four narrowly endemic species and one cosmopolitan species of the rock-dwelling cichlid fish species flock (mbuna) of Lake Malawi in East Africa. The endemics, restricted to very small islands, appear to have originated less than 20,000 yr ago. Relative and absolute levels of genetic diversity were used to examine the possibility that these endemics arose through founder events, as has been suggested for the Hawaiian drosophiloids, to which the East African cichlids have been compared. Three principal results emerged from this study. First, the undescribed species Pseudotropheus zebra 'black dorsal' was found to be depauperate of mtDNA haplotype diversity relative to sister taxa, suggesting a severe population bottleneck during, or subsequent to, its recent origin. Second, significant differences in haplotype frequency existed among all five closely related species examined here. Geologic evidence and distributional limits indicate that this divergence in haplotype frequency occurred rapidly, consistent with population bottlenecks. Paradoxically, in three of four species examined there was no apparent reduction in genetic diversity, and two had haplotype diversity values that were high relative to other freshwater fishes. Third, it was found that replicate collections of single species at different sites within the same general locations, without obvious barriers to gene flow, also exhibited significant differences in haplotype frequency. Such apparent fine-scale genetic structuring, whether spatial or temporal, has substantial implications for estimates of effective population size and modeling of speciation processes.




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