Meeting Abstract

P1.5  Jan. 4  The Ontogeny of Developmental Plasticity in Amphibians LEDON-RETTIG, C.C.*; PFENNIG, D.W.; NASCONE-YODER, N.; UNC, Chapel Hill; UNC, Chapel Hill; North Carolina State Univ. ledonret@email.unc.edu

Anuran larvae typically develop a long coiled gut that is considered adaptive for organisms with a low quality diet of detritus. As the tadpole undergoes metamorphosis and adopts a carnivorous diet, the gut is remodeled into the shorter, less coiled form of an adult. While this transition is canalized in many species, spadefoot toads (Spea) exhibit alternative developmental trajectories, in which larvae that eat fairy shrimp and/or conspecifics can diverge to become a carnivorous tadpole. The carnivore morph develops predatory features, such as behavioral and craniofacial alterations, and a shorter, less coiled gut. Although carnivore induction has been hypothesized to result from precocious metamorphosis, the specific developmental mechanisms underlying this polyphenism are largely unknown. We compared the ontogeny of gut development in the presence and absence of an inducing diet (shrimp) in spadefoot toads (Spea multiplicata and S. bombifrons) that differ in their propensity to develop carnivores, and in a closely related species (Scaphiopus couchii) that is solely omnivorous. After feeding, intestinal elongation proceeded less rapidly in tadpoles that consumed shrimp compared with those that consumed detritus, and this attenuation was observed earlier and more frequently in the species that has the greatest tendency to produce carnivores. These results indicate that the shorter �carnivore� intestine morphology may not be the result of a heterochronic acceleration of the gut shortening that occurs during metamorphosis, but is instead generated by a reduced rate of early gut elongation. Moreover, histological sections of shrimp-fed tadpoles illustrate that intestinal epithelial growth and differentiation is less substantial than in detritus-fed tadpoles, suggesting the larvae’s early physiological response to diet may ultimately contribute to their divergent morphologies.