Drivers and dynamics of a massive adaptive radiation in cichlid fishes

Adaptive radiation is the likely source of much of the ecological and
morphological diversity of life. How adaptive radiations proceed and what
determines their extent remains elusive in most cases. Here we report the
in-depth examination of the spectacular adaptive radiation of cichlid
fishes in African Lake Tanganyika. Based on whole-genome phylogenetic
analyses, multivariate morphological measurements of three ecologically
relevant trait complexes (body shape, upper oral jaw morphology, and lower
pharyngeal jaw shape), scoring of pigmentation patterns, and
approximations of the ecology of virtually all ~240 cichlid species
endemic to Lake Tanganyika, we show that the radiation occurred within the
confines of the lake and that morphological diversification proceeded in
consecutive trait-specific pulses of morphospace expansion. We provide
empirical support for two theoretical predictions on how adaptive
radiations proceed, the ‘early-burst’ scenario (for body shape) and the
stages model (for all traits investigated). Through the analysis of two
genomes per species and by taking advantage of the uneven distribution of
species in subclades of the radiation, we further show that species
richness scales positively with per individual heterozygosity, but is not
correlated with transposable element content, number of gene duplications,
or genome-wide levels of selection in coding sequences.