The Evolution of the Pro-Domain of Bone Morphogenetic Protein 4 (Bmp4) in an Explosively Speciated Lineage of East African Cichlid Fishes

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Abstract
Lakes Victoria, Malawi, and Tanganyika in the East African Rift Valley harbor approximately 200, 400, and 170 endemic species of cichlid fishes, respectively (Fryer and Iles 1972, pp. 1–104; Greenwood 1984, 1991 ), which provide spectacular examples of the explosive adaptive radiation of living vertebrates (Fryer and Iles 1972 ; Greenwood 1984 ). The fishes exploit almost all resources that are available to freshwater fishes in general (Fryer and Iles 1972 ; Greenwood 1984 ), and they are extremely diverse, both ecologically and morphologically, despite having evolved during a very short evolutionary period (Meyer et al. 1990 ; Johnson et al. 1996 ). It has been estimated that the species flocks in Lakes Malawi and Victoria are 700,000 years old (Meyer et al. 1990 ) and less than 12,400 years old (Johnson et al. 1996 ), respectively, and that the species in these lakes have speciated within such very short periods of time. In general, members of a species are defined by their reproductive physiology, sexual behavior, and morphology. Therefore, it is reasonable to postulate that morphogenetic genes responsible for the morphological diversity of cichlid species must have changed at an accelerated rate in parallel with the morphogenetical diversification of species. In an attempt to identify the possible correlation between changes in morphology and changes in genes, we focused on genes responsible for the morphogenesis of the cichlid jaw and dentition as possible candidates. The structure of the cichlid jaw and dentition, i.e., the trophic morphology, vary more considerably among closely related cichlid species in an explosively speciated lineage of East Africa than in species inhabiting rivers (Fryer and Iles 1972 ; Greenwood 1984 ).