Larval diet of the frog Alsodes gargola (Leptodactylidae: Telmatobiinae) and some ecological considerations on its role in alpine and mountain aquatic environments in Patagonia

Abstract

AbstractAlsodes gargola is an endemic species from northwest Patagonia, Argentina. Its tadpoles inhabit oligotrophic high altitude lakes and mountain streams from their sources. Tadpole diet is an important yet still unknown feature of its biology. This study analyzes alimentary tract content from A. gargola tadpoles collected from several of the species' typical habitats. For each group of items eaten, frequency of occurrence and its importance in the diet according to biovolume was calculated. Tadpole feeding behavior was also observed. The most common items were periphyton and plant material. The predominant algae were diatoms (typically periphytic), chlorophytes (periphytic and some planktonic) and a few cyanobacteria. Planktonic components were found in low proportion in all samples. The animal component (mainly from periphyton) was represented by ciliates, flagellates and amoebae, and varied according to the habitats, as did vascular plant fragments. There was a wide size range of ingested particles (from 10 to 400 μm) and a wide variety of components, according to the features of each habitat. These results suggest that tadpole of A. gargola are grazers of the periphytic community and detritus gatherers. The larval diet matches the tadpole's morphological and structural adaptations to a lotic-benthic habitat (depressed body, ventral subterminal oral disc capable of adherence, dorsal eyes, low, subparallel fins) and direct observation of behavior in natural environments (slow-swimming bottom-dwelling tadpoles in still water or streams with slow-flowing microhabitats). We discuss the ecological role of slow-developing tadpoles (regulation of periphyton development), which attain large biomass in their particular ecosystems, where they are the only aquatic vertebrates.