Extant holocephalans are an anatomically bizarre group of deep sea dwelling fishes which are highly adapted to durophagy, and extraordinarily slow-evolving. They are also the tip of a lineage which has survived three big mass-extinctions. Thus, holocephalans have great potential as a case study in how evolution shapes morphology in response to selection pressures over vast periods of time, and how this morphology is affected by mass extinction events. We will bring together new collaborations to investigate the relationship between the form of the holocephalan skull and jaws and their function in durophagy. We will take a novel approach based around three objectives: functional morphology, ontogeny, and paleontology. The methods we will use have never been applied to this question before. We expect this project to lay the groundwork for future collaboration between our teams, as well as helping to develop the application of similar modelling methods to other fields of paleontology.

In frogs, acoustic communication is important in the context of sexual selection and species recognition. Understanding the binaural hearing system in frogs is a major challenge. Indeed, some of the fundamental mechanisms of hearing remain partly or totally unclear. Sound can reach the inner ear by means of multiple pathways, i.e. tympanic and extratympanic pathways. Our project aims to develop non-invasive, non-destructive methods to observe the ear and understand the reception and localization of sounds in anurans. The first step of the project will focus on auditory and sound localization capacities of frogs. The second step will focus on binaural sound reception. The third step aims at testing the models established in vivo thanks to complementary experiments and the development of an X-ray imaging technique to visualize middle ear movements during acoustic stimulations. Each of these steps involves different tools and techniques to characterize the auditory system of frogs.

Organisms are subjected to both intrinsic and extrinsic constraints during their life-time as well as in an evolutionary context. According to the constructional morphology model of Seilacher (Seilacher, 1970; Gould, 2002; Cubo, 2004), biological features are considered as the outcome of phylogenetic, adaptative, and architectural constraints, referred to as historical, functional, and structural constraints by Gould (2002). This is also the case for bone microanatomical and histological features, i.e. the internal organization of bone and the specific features of the osseous tissues. Bone is a living structure and thus records information about the biology and ecology of the organisms (e.g. type and speed of growth, age at sexual maturity, life history, physiology, mechanical constraints, etc...). Bone is, in fact, a very plastic structure. Thus, microanatomical specializations are thought to occur before large-scale anatomical ones, such that bone microanatomy can be used as a tool to understand the initial stages of adaptation to, for example, a new environmental context (e.g. aquatic versus terrestrial). The adaptation to specific environments has happened several times independently in various lineages of tetrapods. If several of the associated features are nowadays observable in modern forms, fossil taxa are essential to complete our knowledge and in order to understand the evolutionary processes involved. The current project proposes to focus on secondary adaptation to an aquatic life in amniotes and, more specifically on the adaptations to a semi-aquatic life style in mammals. By linking microanatomical specializations with the specific functional requirements of locomotion in semi-aquatic amniotes using available ecological data and in vivo studies we aim to gain insights on the ecology of fossil taxa. More specifically, we aim to understand transitional forms in the process of a secondary adaptation to an aquatic life and the different steps of adaptation to this new milieu in different lineages. The larger objective is to understand the adaptation of bone to intrinsic (e.g. phylogenetic, behavioural) and extrinsic (e.g. environmental) constraints in the process of secondary adaptation to an aquatic life, a major theme in evolutionary biology.

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.