Functional Indices and Postnatal Ontogeny of Long Bones of the Forelimb in the Sigmodontine Rodents (Rodentia: Cricetidae)

Abstract

The adaptations for a particular locomotor type (e.g., fossorial or saltatorial) could affect limb bone morphology throughout ontogeny. We explore how the measurements of the forelimbs and functional indices change along the postnatal ontogeny of 92 specimens of sigmodontines belonging to four genera (Akodon, Eligmodontia, Oligoryzomys, and Oxymycterus) with different locomotor types (ambulatory, quadrupedal-saltatorial, scansorial, and semifossorial). We examined individuals of different age categories: juveniles, young adults, and adults. Eleven linear measurements of long bones (humerus, radius, and ulna) corresponding to functional diameters and lengths were taken and analyzed through simple regressions (RMA) using geometric mean transformations. Six morphofunctional indices were then calculated and analyzed through multivariate analysis (MANOVA). The allometric patterns and morphofunctional indices show that the forelimb tends to be elongated and slender in the ambulatory, scansorial, and quadrupedal-saltatorial species, and short and thicker in the semifossorial species. Morphofunctional indices do not separate our sample concerning age categories, possibly indicating that the juveniles of different rodent species are born with similar morphology to the adults in terms of locomotion.