CE02 - Terre vivante

The return to an aquatic life, the evolution of propulsive efficiency & biomimetics – DRAGON2

Submission summary

The return to an aquatic life has shaped many organisms and profoundly impacted fossil and extant marine ecosystems. Understanding how terrestrial organisms adapted to a drastically novel environment poses fundamental challenges, however. Indeed, in most lineages this major transition entailed deep alterations of locomotor modes that impede straightforward comparisons among evolutionary stages. Snakes constitute an exception. A single undulatory locomotor mode is efficient both on land and in water. Our key hypothesis is that the return to an aquatic life, frequently observed in snakes, was mediated by the optimization of the undulatory kinematics without a radical alteration of this locomotor mode. We postulate that optimized undulations minimize resistance and maximize propulsive drag. Energetic efficiency of swimming should thus be higher in aquatic species compared to closely related terrestrial species. Yet, quantifying swimming performance, undulatory kinematics and energetic expenditure simultaneously is technically challenging, especially using non-invasive techniques. Furthermore, physical effort can be partly decoupled from oxygen consumption in snakes, making classical techniques (e.g. respirometry) imprecise. One option is to measure the drag coefficient of swimming animals: the vortical structures produced at each time interval may be use to accurately quantify the efficiency of locomotion. Thus, fluid mechanics and numerical modelling are alternatively solutions allowing to tackle this complex problem involving deformable structures. This fundamental project based on biology and fluid mechanics also relies on robotics. Bio-inspired snake-robots will be designed to experimentally assess the relationship between kinematics, energy expenditure and hydrodynamic drag. This multidisciplinary project includes 5 work-packages. WP1: motion capture and 3D-kinematic analyses will be used to analyse the undulatory kinematics (frequency, amplitude) of swimming snakes in the laboratory. Drag will be measured using volumetric particle image velocimetry. A range of terrestrial, amphibious and aquatic species will be tested. WP-2: key parameters obtained in WP1 will be used to design swimming robots to test the influence of swimming kinematics on propulsive and resistive forces. WP-3: skin surface structure of a wide diversity of snakes will be examined using scanning electron microscopy, micro-CT scans and gel-based stereo-profilometry. 3-D reconstructions of skin surfaces will be tested in a flow tunnel to examine their tribological properties. WP-4: the information collected will provide the basis for numerical simulation analyses of the energetic efficiency of displacement. The objective is to develop a predictive model that integrates body size, body shape, skin structure, undulatory kinematics to obtain the energetic efficiency of any swimming snake (or robot). Ultimately, we plan to automatically extract and analyse undulatory kinematics from videos of swimming snakes to derive the cost of transport associated. WP-5. the predictive model will be used to estimate the swimming efficiency of a large number of species for which video records will be obtained in the field. The large and unique collection of kinematics representative of the extraordinary diversity exhibited by snakes will allow us to frame analyses into a phylogenetic context. Factors like body size, foraging mode, reproductive status, and sex will be implemented. This huge data set will also provide multi-optimization criteria for robot prototypes. The numerical codes developed during this project and the data bases will be registered (INPI). Besides fundamental objectives in evolutionary biology, this project based on state-of-the-art techniques and measurements on living snakes to understand the hydrodynamic efficiency of undulatory swimming represents a unique opportunity for French laboratories to participate in the race to develop snake-robots.

Project coordination

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.


PMMH Laboratoire de Physique et Mécanique des Milieux Hétérogenes
INRIA Bordeaux Sud-Ouest Centre de Recherche Inria Bordeaux - Sud-Ouest
Pprime Institut P' : Recherche et Ingénierie en Matériaux, Mécanique et Energétique
CEBC Centre d'études biologiques de Chizé
MECADEV Mécanismes Adaptatifs et Evolution

Help of the ANR 599,400 euros
Beginning and duration of the scientific project: December 2020 - 48 Months

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