Cichlid Evolution: Lessons in Diversification

With an estimated 3000 species, distributed from Central and South America, across Africa to Madagascar, the Middle East, and southern India, cichlid fishes (Cichlidae) represent the most species-rich family of vertebrates. In total they account for about 10% of extant teleost diversity. Throughout their distributional range, cichlids have repeatedly demonstrated their capacity for undergoing adaptive radiation, generating an outstanding variation of body shapes, color patterns, and behavior, and an enormous diversity of trophic and ecological specializations. This has made them an important model system for the field of evolutionary biology. With the completion of the first cichlid genome sequences, cichlid fishes are likely to receive even more attention in evolutionary research. This special issue presents a collection of papers that tackle various aspects of cichlid biology essential for gaining a deeper understanding of factors and processes responsible for generating their diversity. Naturally, the selected topics and papers do not fully represent all fields of research that have contributed to our understanding of cichlid evolution. Nevertheless, they do represent rich and diverse knowledge which we are pleased to share with the readers of IJEB. Papers are summarized below in the order in which they appear in this special issue. Lake Tanganyika is the oldest of the three East African Great Lakes and harbors the morphologically, behaviorally, ecologically, and genetically most diverse lacustrine cichlid species assemblage. In their review, " The adaptive radiation of cichlid fish in Lake Tanganyika: a morphological perspective, " T. Takahashi and S. Koblmüller give a brief overview about recent phylogenetic findings and provide a synthesis of morphological studies that relate to the adaptive radiation of Lake Tanganyika's cichlids. They discuss many of the relevant studies that have contributed to our increasing knowledge of the evolutionary pathways and mechanisms generating this exceptional diversity within a short period of time. Furthermore, the authors highlight the potential importance of ontogenetic changes in morphology for establishing taxa in complex species-rich communities, a largely neglected issue in East Africa's species-rich lacustrine cichlid species assemblages. Recent advances in morphometric methods provide great potential for detailed analyses of cichlid anatomy in an evolutionary context. In particular the establishment of geometric morphometric approaches has revolutionized the analysis of morphological data in cichlid evolutionary research. In their review, " The utility of geometric morphometrics to elucidate pathways of cichlid fish evolution, " M. Kerschbaumer and C. Sturmbauer introduce geometric morphometric concepts and methods and also provide …