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In nature, tadpoles encounter food on substrates oriented at different angles (e.g. vertically along stems, horizontally on the bottom of the pond). We manipulated the orientation of food-covered surfaces to test how different orientations of surfaces affect tadpoles' feeding efficiency. We studied taxa that differed in the oral morphology of their larvae and position in the water column. We hypothesized that species would differ in their ability to graze upon surfaces at different orientations and that differences in the tadpoles' feeding ability would result in different growth rates. The orientation of food-covered surfaces did not affect the growth rate of bottom-dwelling tadpoles (whose growth rate varied only between species). Among midwater tadpoles, some species appear to have a generalist strategy and experienced a high relative growth rate on numerous substrate orientations, whereas others achieved high growth rates only on flat substrates (i.e. at 0° and 180°). We conclude that oral morphology constrains tadpoles' ability to feed at different substrate orientations, and this could lead to niche partitioning in structurally complex aquatic environments. Because physical parameters of the environment can affect tadpoles' growth rate, characterizing these features might help us better understand how competition structures tadpole assemblages.

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One of the many taxonomic challenges found in the Dendropsophus microcephalus species group is the Dendropsophus walfordi distinction from D. nanus. Recent phylogenetic inferences have indicated the paraphyly of these species, although they were not designed to assess this issue. To contribute to the delimitation of these species, we analyzed the 12S, 16S and COI mitochondrial genes, the morphological traits, and the advertisement calls of specimens from northern Amazonia to Argentina, including the type localities of D. nanus and D. walfordi. Paraphyly of D. nanus with respect to D. walfordi was inferred by maximum-parsimony and Bayesian analyses, and five major clades exhibiting nonoverlapping geographic distributions were recognized. The bPTP and ABGD analyses supported the existence of five independently evolving lineages in this complex. Acoustic and morphological data clearly distinguished the clade that included the topotypes of D. walfordi from the others, corroborating the validity of this species. To avoid the paraphyly of D. nanus with respect to D. walfordi, we recognize the clade distributed from central-southern Brazil to Argentina as D. nanus, the clade distributed in Amazonia as D. walfordi, and discuss the existence of unnamed cryptic species closely related to D. nanus and D. walfordi.

Two of the most fundamental questions in tadpole biology, also applicable to most small, under‐studied organisms are: (1) ‘Why are they built the way they are?’ and (2) ‘Why do they live where they do?’ Regrettably, despite significant progress in most aspects of tadpole biology, the answers to these questions are not much better now than they were in the last century. We propose that an autecological approach, that is the careful observation of individuals and how they interact with the environment, is a potential path towards a fuller understanding of tadpole ecomorphology and evolution. We also discuss why more attention should be given to studying atypical tadpoles from atypical environments, such as torrential streams, water‐filled cavities of terrestrial plants and wet rock surfaces neighbouring streams. Granted, tadpoles are rare in these settings, but in those unusual habitats the physical environments can be well described and characterized. In contrast, the more common ponds where tadpoles are found are typically too structurally complex to be easily delineated. This makes it difficult to know exactly what individual tadpoles are doing and what environmental parameters they are responding to. Our overall thesis is that to understand tadpoles we must see exactly what they are doing, where they are doing it, and how they are doing it. This takes work, but we suggest it is feasible and could greatly advance our understanding of how anuran larvae have evolved. The same strategies for studying tadpoles that we encourage here can be applied to the study of many other small and fast‐moving animals.