Morphometric Variation in Pleurodema (Anura: Leptodactylidae: Leiuperinae): Evidence of Fossoriality?

Abstract

Anurans that inhabit dry habitats exhibit particular life histories and possess morphological features associated with burrowing behavior (e.g., specialized metatarsal tubercles, short hind limbs relative to body size). The Neotropical genus Pleurodema includes 15 species distributed mainly in arid and semiarid environments. Backward burrowing behavior has been recorded in the genus, as well as the presence of specialized inner metatarsal tubercles. However, morphometric variation associated with burrowing has not been sufficiently studied in Pleurodema. To explore this variation, we scored 13 external body measurements and examined the morphology of the metatarsal tubercles of 615 adult specimens representing 14 species of Pleurodema. We also summarized available data about egg-clutch structure, hatching time, and duration of larval period of all species of the genus. Our results revealed that body shape variation mainly consists of differences in the relative length of the hind-limb elements. Pleurodema brachyops, P. diplolister, P. guayapae, P. nebulosum, P. tucumanum, and P. marmoratum have the shortest hind-limb elements relative to snout-vent length, and all but P. marmoratum also have keratinized inner metatarsal tubercles. The combination of these features has been considered a fossorial specialization on biomechanical grounds. Pleurodema brachyops, P. diplolister, P. guayapae, P. nebulosum, and P. tucumanum also have the shortest hatching time and larval period. A short larval period has been related to arrestment in the elongation phase of anuran limbs. Both burrowing performance and developmental effects could explain the variation in the limb morphology within Pleurodema.