Another one bites the dirt: a closer look into geophagy in tadpoles of Thoropa miliaris (Spix, 1824).

Geophagy, the ingestion of earthy materials such as soil or sand, is present in different animal groups, including adult frogs and their larvae. In some species, the ingestion of sediments is an intrinsic aspect of the biology of these animals. During an investigation on aspects of the natural history and morphology of tadpoles of Thoropa miliaris (Cycloramphidae) we noticed that their intestines were filled with sediments. The first question that occurred to us involved whether ingestion was accidental or part of their behavioral repertoire. These tadpoles are found in rockfaces wetted by a slow running film of water, where besides a slime film of algae and moss, we do not observe significant accumulation of sediments. Another question involved knowing if the sediments ingested were already available in their habitat, or if they were biting off small pieces of the rocks where they live. To investigate that, we used a combination of light microscopy and synchrotron high-resolution x-ray microtomography techniques to study the morphology of the sediments in the habitat and intestines of 57 tadpoles in different stages of development (all with sediments in their digestive tracts) and based on that, determine its source. Comparisons of geometric features of the sediments on the habitat and in the tadpoles' intestines, favor the hypothesis that its source is already present in the habitat and that it is swallowed as water and food is sucked as part of the tadpole foraging and respiratory behavioral repertoire.