Smooth, rough, or striated: Influence of substrate texture on tadpoles’ growth rates

Tadpoles graze food upon a variety of substrates that differ in surface texture (e.g. smooth leaves, rough rocks). We tested how interspecific variation in the external oral morphology of nine species influenced tadpoles’ growth rate when feeding on smooth, striated or rough substrates. We looked into: differences in (1) emarginations and number of gaps in the marginal papillae rows among species, (2) number of gaps in the labial tooth rows and (3) number of labial tooth rows among species. Species with a single and complete marginal papillae row consumed a high amount of food upon all the substrates tested. Tadpoles with the same marginal papillae row configuration have the same ability to acquire food from the same substrates; tadpoles with more gaps in this soft tissue consumed more food only when grazing on rough substrates. Tadpoles with the same number of labial tooth rows, but different number of gaps in these structures grew well regardless the substrate textures. However, tadpoles with generalized oral configuration, i.e., labial tooth row formula 2(2)/3(1), had higher growth rates than the other species. Tadpoles with a high number of labial tooth rows were generalists in terms of substrate surface textures. Tadpoles with few keratinized structures were specialists on smooth surfaces. We demonstrated that variation in oral morphology influences tadpoles’ ability to acquire food from substrates with different textures, with consequences to growth rate. We provide insights about specializations in feeding behavior and the adaptive significance of variation in external oral morphology.