The cichlid fish communities of the East African Great Lakes are amongst the richest
concentrations of vertebrate species on earth. These "explosive" radiations represent an
unequaled system to address central questions in evolutionary biology, and have therefore
figured prominently in studies of speciation, ecological plasticity, and molecular evolution.
Cichlid radiations in the three major lakes (Victoria, Tanganyika, and Malawi) are generally
similar in terms of trophic diversity, species richness, and rates of endemism. However, being
largely independent of each other, they offer a true evolutionary experiment with treatment
groups and replicates. Using computer-based morphometric methods, we compared brain morphology
among 189 cichlid species from the East African Lakes and Madagascar. The Madagascan taxa were
included as phylogenetically primitive representatives of the family Cichlidae. In this first
paper we report data on the relationship between brain and body size, and address patterns of
brain form variation among individuals, lakes, and sexes. Cichlid faunas of the three lakes,
encompassing 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 variation was observed in the development of association centres,
in particular of the telencephalon. The lack of negative associations among brain regions
across lakes indicated that enhanced development of one brain structure for a particular
function is not compensated for by reduction of other modalities.