Chondrocranial morphology and ontogenetic allometry in larval Bufo americanus (Anura, Bufonidae)

Abstract

Available descriptions of chondrocranial morphology among larvae of Bufo species are inconsistent, the range of variation in chondrocranial structure is not well defined, and no detailed quantitative descriptions of cranial ontogeny currently exist for any species of the genus. This study describes chondrocranial morphology in larval Bufo americanus based on three samples of tadpoles and provides comparisons with other species of Bufo. Additionally, this study provides the first data on ontogenetic allometry of the chondrocranium in Bufo and demonstrates fine-scale intraspecific shape variation among samples of B. americanus larvae. Chondrocranial morphology in B. americanus is overall similar to that reported for larvae of other members of the genus. Morphometric analyses indicate that although chondrocranial shape differs consistently among samples from three localities, patterns of ontogenetic allometry are conserved. Common principal components analysis of the chondrocranial measurements indicates a mixture of allometric and isometric scaling. Measurements associated with the oral region, braincase, and otic capsule tend to scale with negative allometry, whereas those associated with the posterior palatoquadrate and insertion sites for the major jaw and buccal muscles scale with isometry or positive allometry. These data provide further evidence that the anuran chondrocranium is not a static structure during premetamorphic stages. Furthermore, these patterns are similar to those previously reported for Rana sylvatica, suggesting the hypothesis that these allometries may represent a general pattern in larval anurans.