Accelerated brain shape evolution is associated with rapid diversification in an avian radiation

Niche expansion is a critical step in the speciation process. Large brains linked to improved cognitive ability may enable species to expand their niches and forage in new ways, thereby promoting speciation. Despite considerable work on ecological divergence in brain size and its importance in speciation, relatively little is known about how brain shape relates to behavioral, ecological, and taxonomic diversity at macroevolutionary scales. This is due, in part, to inherent challenges with quantifying brain shape across many species. Here, we present a novel, semiautomated approach for rapidly phenotyping brain shape using semilandmarks derived from X-ray computed micro-tomography (microCT) scans. We then test its utility by parsing evolutionary trends within a diverse radiation of birds, kingfishers (Aves: Alcedinidae). Multivariate comparative analyses reveal that rates of brain shape evolution, but not beak shape, are positively correlated with lineage diversification rates. Distinct ...