Environments impact organism diversity and drive convergence—whereby distantly related species share phenotypes due to adaptation to similar environments (e.g. bird, bat wings). Evolutionary studies of ‘environment’ often apply arbitrary categories (e.g. fossorial, arboreal) that vaguely blend biotic and abiotic factors, limiting quantitative studies of form-function links. Innovatively, this project will test the hypothesis that a continuous physical variable (substrate density) has driven head shape adaptation. Under this hypothesis, a density gradient mirrors a phenotypic response gradient. Snakes are a superb system to study head shape adaptations because of: 1) spectacular taxonomic and phenotypic diversity, including many independent origins of aquatic and burrowing forms, and 2) limblessness, requiring snake heads to adapt to demands for locomotion as well as feeding, and protecting sensory organs. Similarities in aquatic and burrowing snake heads have been explained by adaptation to mostly unspecified environmental factors. Testing the hypothesis that variation in head shape is explained by substrate density will provide a fresh perspective on debates about the possibly aquatic or burrowing origin of snakes. I will quantify: a) head shape of snakes living in substrates of various densities, b) mechanical forces undergone by heads and skulls during headfirst locomotion, c) integration among head, skull and braincase shape. These data will be analysed in a comparative phylogenetic framework. HeadStrong combines 3D imaging, mechanics experiments with a snake-like robot and computer simulations that will be performed in globally leading institutions with unrivalled resources in terms of a vast reptile collection, outstanding imaging facilities, and expert staff. HeadStrong’s originality and interdisciplinary nature will generate exceptional datasets and high-profile outputs and establish the applicant as an innovative leader in functional biology.
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