Replicated functional evolution in cichlid adaptive radiations

Adaptive radiations highlight the mechanisms by which species and traits
diversify and the extent to which these patterns are predictable. We used
1,110 high-speed videos of suction feeding to study functional and
morphological diversification in 300 cichlid species from three African
Great Lake radiations of varying ages (Victoria, Malawi and Tanganyika)
and an older, spatially dispersed continental radiation in the Neotropics.
Among African radiations, standing diversity was reflective of time.
Morphological and functional variance in Lake Victoria, the youngest
radiation, was a subset of that within Lake Malawi, which itself was
nested within the older Tanganyikan radiation. However, functional
diversity in Neotropical cichlids was often lower than in Lake Tanganyika,
despite being much older. These two radiations broadly overlapped, but
each diversified into novel trait spaces not found in the youngest lake
radiations. Evolutionary rates across radiations were inversely related to
age, suggesting extremely rapid trait evolution at early stages,
particularly in lake radiations. Despite this support for early bursts,
other patterns of trait diversity were inconsistent with expectations of
adaptive radiations. This work suggests that cichlid functional evolution
has played out in strikingly similar fashion in different radiations, with
contingencies eventually resulting in lineage-specific novelties.