The impact of diet, habitat use, and behaviour on head shape evolution in homalopsid snakes

Abstract

An organism's morphology is driven by selection on function while being constrained by phylogenetic and developmental factors as well as functional trade-offs. If selection on function is strong and solutions limited, then convergence is expected. In this paper we quantify head shape in a group of ecologically diverse snakes (homalopsid snakes) differing in habitat use and diet using three-dimensional geometric morphometric approaches. Using data on head shape we explore whether snakes eating different prey show different morphologies. Moreover, we test whether head shape is constrained by other factors such as habitat use, burrow use, or activity pattern. Our results demonstrate similar head shapes in species consuming similar prey. Snakes that capture elusive prey under water differ from those that capture and swallow prey like frogs or crustaceans. Moreover, habitat use, the use of burrows, and activity pattern also significantly impact head shape in this group of snakes. However, this signal appears to be partly confounded by the diet signal. For axes discriminating specifically between habitat use groups or animals that use burrows vs. those that do not shapes were in accordance with our predictions. Our results suggests an adaptive signal in the evolution of head shape in homalopsid snakes with diet, habitat use and the use of burrows all influencing the evolution of head shape in the group.