Tempo and mode of evolution across multiple traits in an adaptive radiation of birds (Vangidae)

An ongoing challenge in macroevolutionary research is identifying common
drivers of diversification amid the complex interplay of many potentially
relevant traits, ecological contexts, and intrinsic characteristics of
clades. In this study, we used geometric morphometric and phylogenetic
comparative methods to evaluate the tempo and mode of morphological
evolution in an adaptive radiation of Malagasy birds, the vangas, and
their mainland relatives (Aves: Vangidae). To characterize the
morphological diversity of the clade we used both landmarks and
semilandmark curves from the bill and neurocranium, and linear
measurements of pedal bones, all collected from microCT scans of museum
specimens. The Malagasy radiation is more diverse in both skull and foot
shape. However, rather than following the classic "early burst"
of diversification, trait evolution accelerated well after their arrival
in Madagascar, likely driven by the evolution of new modes of foraging and
especially of a few species with highly divergent morphologies. Anatomical
regions showed differing evolutionary patterns, and the presence of
morphological outliers impacted the results of some analyses, particularly
of trait integration and modularity. Our results demonstrate that the
adaptive radiation of Malagasy vangas has evolved exceptional
ecomorphological diversity along multiple, independent trait axes, mainly
driven by a late expansion in niche space due to key innovations. Our
findings highlight the evolution of extreme forms as an overlooked feature
of adaptive radiation warranting further study.