Influence du mode de vie sur les caractéristiques pondérales et structurales du squelette chez les amphibiens anoures
To specify the influence of a permanent aquatic life on skeletal mass and bone structure in anuran amphibians, the general and regional masses of the skeleton, as well as several histomorphometric indices of the bones (porosity, corticodiaphyseal index, density) were compared in four ranid species, two predominantly aquatic (Rana perezi and R. esculenta) and two more terrestrial (R. temporaria and R. dalmatina). The relative mass of the skeleton (as a percentage of the total body mass) is significantly lower in aquatic forms. This difference is not a phenomenon of intra- or inter-specific allometry between skeletal mass and body mass (size effect). Rather, it reflects a selective reduction of skeletal volume (low corticodiaphyseal index values and higher porosity), in particular in the autopodia, pectoral girdle, front limbs, and vertebral column of aquatic forms. These results reinforce the idea that habitat and mode of life are selective factors producing a more or less developed skeleton in anurans. Whether a lighter skeleton is a permanent adaptative feature or a reversible response in predominantly aquatic anurans remains to be tested.