Meeting Abstract
Cranial evolution is hypothesized to be strongly linked to trophic ecology, as evidenced by such key examples as Galapagos finches and Hawaiian honeycreepers. However, this hypothesis is rarely tested at macroevolutionary scales. Here, we interrogate the relationship between diet, foraging ecology, and cranial phenotype across extant birds. We utilize high-dimensional geometric morphometric data (>700 3D landmarks) quantifying skull shape in 352 bird species, spanning the breadth of phenotypic variation in the crown group. We demonstrate that diet and foraging behavior are significant, but surprisingly very weak predictors of skull shape (p < 0.001, R2 < 0.09). However, rates of evolution vary more substantially across dietary niches. This is especially pronounced in the face and cranial vault regions of the skull, where granivores and nectarivores exhibit the highest rates of evolution and terrestrial carnivores evolve the slowest. Other regions of the skull, including basisphenoid, occipital, pterygoid, and quadrate, show less pronounced differences among trophic guilds. These findings suggest that the strength of selection imposed by trophic ecology differs across skull regions/modules and across niches. Dietary groups with high rates of facial evolution are those that include strong mechanical constraints (crushing seeds) or geometric constraints (coevolution between flowers and nectarivores). Taken together, these results illustrate how dietary ecology and complex adaptive landscapes influence the tempo and mode of phenotypic evolution and how big-data approaches can inform our understanding of macroevolutionary processes.
