BRAIN EVOLUTION IN CICHLIDS OF THE AFRICAN GREAT-LAKES - BRAIN AND BODY-SIZE, GENERAL PATTERNS, AND EVOLUTIONARY TRENDS

The cichlid fish communities of the East African Great Lakes are among st the richest concentrations of vertebrate species on earth. These '' explosive'' radiations represent an unequaled system to address centra l questions in evolutionary biology, and have therefore figured promin ently in studies of speciation, ecological plasticity, and molecular e volution. Cichlid radiations in the three major lakes (Victoria, Tanga nyika, and Malawi) are generally similar in terms of trophic diversity , species richness, and rates of endemism. However, being largely inde pendent of each other, they offer a true evolutionary experiment with treatment groups and replicates. Using computer-based morphometric met hods, we compared brain morphology among 189 cichlid species from the East African Lakes and Madagascar. The Madagascan taxa were included a s phylogenetically primitive representatives of the family Cichlidae. In this first paper we report data on the relationship between brain a nd body size, and address patterns of brain form variation among indiv iduals, lakes, and sexes. Cichlid faunas of the three lakes, encompass ing three putative subfamilies, exhibit surprisingly similar variation in the form of brain structures concerned with vision, olfaction, and the lateral line. However, across the African lakes, the greatest var iation was observed in the development of association centres, in part icular of the telencephalon. The lack of negative associations among b rain regions across lakes indicated that enhanced development of one b rain structure for a particular function is not compensated for by red uction of other modalities.