Morphological Differentiation and Adaptation of the Larvae of Rana berlandieri and Rana sphenocephala (Rana pipiens complex) in Sympatry

pipiens complex, were analyzed for morphological differentiation using multivariate techniques. Field-collected and laboratory-reared larvae of both species were compared for 12 morphometric characters. R. berlandieri larvae differ from R. sphenocephala larvae in having a more fusiform body shape, greater tail musculature development, a longer tail, relatively narrow dorsal and ventral tail fins, a shorter gastrointestinal tract length, fewer oral papillae on the lower labium, and a smaller ratio of interocular distance/ internareal distance. The number of oral papillae, however, is phenotypically plastic and probably varies with diet or mode of feeding. Pigmentation differences include tail blotching in R. berlandieri vs relatively uniform melanophore distribution in the tail fin of R. sphenocephala. Most of the morphological differentiation can be explained on the basis of larval habitat and dietary differences between these two species. R. berlandieri larvae are stream-adapted and probably more benthivorous than are the pond-adapted, planktivorous R. sphenocephala larvae.