HeadStrong · On the head of snakes: form, function and adaptation to life in dense media

On the head of snakes: form, function and adaptation to life in dense media

Context Animals that live in dense media such as water, sand or soil undergo strong mechanical forces, especially during locomotion. Despite this, many snake species can burrow or swim efficiently. Because snakes lack limbs, their heads must face the environmental constraints associated with locomotion and this makes the snake head is an excellent system in which to study how physical characteristics of the environment shape phenotypic adaptation. Several studies on different aspects of snake head morphology have demonstrated similarities between fossorial and aquatic snakes. Yet, none of these studies have explored the hypothesis of a functionally driven convergence in response to a shared environmental constraint. Overall, the link between snake morphology and functional demands imposed by the physical properties of their habitat has been largely understudied. Most previous comparative work found a relationship between the shape of head structures in snakes and their ecology, but none has investigated functional hypotheses that could explain these results. On the other hand, the ability of snakes to move efficiently has fascinated engineers and physicists who have studied the detailed kinematics of snake locomotion in different substrates. Yet these functional studies lack a comparative morphological context because they focused on only a small range of species and largely not from an evolutionary perspective. This project aims to fill the gap between these two worlds by revealing the links between head morphology and the biomechanical requirements of environments for snakes. HeadStrong will test the explicit hypothesis that substrate density has driven the evolution of the head and skull shape of snakes. Objectives The main goal of this project is to compare the shape of the skull of many species of snakes that inhabit various substrates and to highlight the specific adaptations related to locomotion in these substrates. To achieve this, HeadStrong has been designed with four Research Objectives: 1) Is the shape of the braincase related to locomotor substrate in snakes? The first objective of HeadStrong is to characterize the link between substrate density and skull shape. 2) Are the inner and outer layers of the braincase independent in shape? The braincase of snakes plays two major roles; providing support for locomotion and hosting and protecting the brain. It is thus composed of an outer layer -the exocranium—the shape of which should be related to locomotor abilities while the inner layer –the endocranium—hosts and protects the brain. The second objective is to evaluate whether the inner and outer layer covary in shape more strongly when the animals undergo a strong mechanical constraint. 3) Does the force needed to penetrate a substrate depend on shape and substrate properties? Once the links between shape and locomotor substrate are highlighted, to demonstrate that these differences in shapes are the results of an adaptation to the mechanical constraints related to each substrate, I will measure the efficiency of each shape to penetrate the different substrates. This will allow an assessment of the adaptation of the skull to locomotion in dense substrates. 4) How good is the braincase at protecting the brain? Because the skull has a second crucial role –protecting the brain—I will compare the efficiency of each braincase shape to reduce and distribute the stress and strain on the brain and soft sensory tissues using mechanical simulations.

Текст от CORDIS, на английски · Данни: CORDIS, © Европейски съюз