▪ Abstract  Cichlid fishes (Perciformes: Teleostei) found in the lakes of Africa have served as model systems for the study of evolution. The enormous number of species (1000 in Lake Malawi alone), the great diversity of trophic adaptations and behaviors, and the extreme rapidity of their divergence (<50,000 y for some faunas) single out these organisms as examples of evolution in progress. Because these fishes are confined to discrete lacustrine environments and their origination is bounded by geological features, these groups provide models with which to study evolution. We review theoretical studies and empirical research on the cichlid faunas of Africa to provide a synthetic overview of current knowledge of the evolutionary processes at work in this group. This view provides the critical information needed to formulate and test hypotheses that may permit discrimination among the diverse theories and models that have been advanced to explain the evolution of these fishes.

The importance of species recognition to taxonomic diversity among Lake Malawi cichlids has been frequently discussed. Hybridization - the apparent breakdown of species recognition - has been observed sporadically among cichlids and has been viewed as both a constructive and a destructive force with respect to species diversity. Here we provide genetic evidence of a natural hybrid cichlid population with a unique colour phenotype and elevated levels of genetic variation. We discuss the potential evolutionary consequences of interspecific hybridization in Lake Malawi cichlids and propose that the role of hybridization in generating both genetic variability and species diversity of Lake Malawi cichlids warrants further consideration.

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One of the most compelling features of the cichlid shes of the African Great Lakes is the seemingly endless diversity of male coloration. Colour diversi cation has been implicated as an important factor driving cichlid speciation. Colour has also been central to cichlid taxonomy and, thus, to our concept of species diversity. We undertook a phylogeographical examination of several allopatric populations of the Lake Malawi cichlid Pseudotropheus zebra in order to reconstruct the evolutionary history of the populations, which exhibit one of two dorsal n colours. We present evidence that populations with red dorsal ns (RT) are not monophyletic. The RT population de ning the northern limit of the distribution has evidently originated independently of the southern RT populations, which share a common ancestry. This evidence of species-level colour convergence is an important discovery in our understanding of cichlid evolution. It implies that divergence in coloration may accompany speciation, and that allopatric populations with similar coloration cannot be assumed to be conspeci c. In addition to this nding, we have observed evidence for introgression, contributing to current evidence that this phenomenon may be extremely widespread. Thus, in species-level phylogenetic reconstructions, including our own, consideration must be given to the potential effects of introgression.

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