Growth and form in Marmota (Rodentia, Sciuridae) : ontogenetic and phylogenetic implications of the mandible geometric morphometrics [Croissance et forme chez Marmota : implications ontogénétique et phylogénétique de la morphométrie géométrique de la mandibule].

Résumé

Geometric morphometrics techniques were applied in a comparative study of the marmot mandible morphology. Post-natal growth of the mandible was studied in M. flaviventris : the sexual dimorphism was moderate, while shape differences among age classes were highly significant and mainly due to ontogenetic scaling.The adults of all the 14 living marmot species were compared and their mandible mean forms used to investigate the morphological evolution of the genus Marmota. Two major trends can be outlined.1) The phylogenetic signal in the variation of the landmark geometry, which describes the mandible form, seems to account for the shape differences at higher taxonomic levels: the subgenus Marmota, recently proposed on the basis of mitochondrial cyt b sequence, is supported by the mandible morphology, moreover, when other sciurid genera are included in the analysis, also the monophyly of the genus Marmota and that of the tribe Marmotinae (i.e., marmots, prairie dogs and ground squirrels) are strengthened by the morphological data. 2) Allopatric speciation in peripheral isolates may have acted as a powerful shape modelling force. This is strongly suggested by the peculiar mandible of M. vancouverensis and, in a lesser degree, by that of M. olympus, which are thought to have originated as isolated populations in Pleistocene ice-free refugia.