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Tadpole diet is likely to vary in response to environmental conditions and nutritional needs throughout growth and development. We investigated seasonal variation in diet composition of Bokermannohyla saxicola tadpoles and compared diets between two developmental stages with a significant difference in size. We found that the diet of B. saxicola tadpoles was dominated by periphytic algae, in accordance with their benthic habits. Considering number of cells ingested, tadpole trophic niches were broader in more advanced developmental stages. Tadpole trophic niches were narrower during the summer (wet season) than during the winter (dry season), which may reflect increased consumption of more energetic food items during the warm period when primary productivity is expected to be higher. Tadpole metabolism is likely to be higher in the summer and increased energetic needs might be supplied in this manner. However, results differed when biovolume was considered instead of number of cells ingested, with larger items assuming a greater importance and niches being usually larger in the summer. In these cases, the increased ingestion of diatoms (likely to be more nutritive) in the summer may decrease the relative importance of large algae (e.g., Mougeotia sp.) that form the bulk of the diet. Both food availability/accessibility and tadpole feeding behaviour driven by nutritional needs may influence patterns of food acquisition. Given the importance of biofilms to tadpole diet, studies on the mechanisms by which tadpole nutritional needs and environmental conditions interact are likely to provide important insights into the dynamics of aquatic food webs. [ABSTRACT FROM AUTHOR]

We investigated how tadpoles of Bokermannohyla martinsi (Martin's Treefrog) and Bokermannohyla nanuzae (Jaboticatubas Treefrog) respond to a simulated predator attack. We tested whether escape variables (depths of microhabitats used, promptness to react, and distance covered while fleeing) varied throughout the year, depended on tadpole size, or both. We expected these variables to be relatively constant throughout the year and that smaller individuals would react more promptly to the stimulus, as they are likely more vulnerable to a broader set of predators. We compared depths used by tadpoles before and after fleeing and expected them to move to deeper microhabitats if depth confers extra protection. We also expected tadpoles positioned at deeper microhabitats to take longer to react and to move less. When comparing the two species, we expected the tadpoles of B. nanuzae, which are potentially cryptic to predators, to take longer to react and to flee shorter distances. We also recorded and compared types of stream substrates used before and after escape by each species and compared the two species regarding microhabitat (bottom type and depth) use. Microhabitat preferences differed between species, but microhabitat types were used in the same proportion before and after fleeing by both species. They showed similarity in promptness to react and distance covered while fleeing from a threat, suggesting that their different coloration does not lead to differentiation in these variables. [ABSTRACT FROM AUTHOR]

Phenotypic plasticity can improve fitness in unstable environments and can be expressed in many traits, such as life history attributes, growth and behavioural features. Microhabitat choice can have important consequences for development and survival of aquatic organisms and is expected to vary in response to stimuli, such as predation risk, food availability and temperature. At seasonal sites, microhabitat availability and associated benefits may change from season to season, which might lead to altered patterns of microhabitat use by tadpoles. We investigated this hypothesis in 17 streams from two localities in south-eastern Brazil. We tested whether water level drops significantly during the dry season, whether lower water level results in altered microhabitat availability and whether predation risk changes between seasons, based on predator density. We then tested whether tadpoles change their pattern of microhabitat use, their spatial niche breadth (given by diversity of used microhabitats) and spatial niche overlap (in the case of co-occurring species). We were able to include in our analyses tadpoles of four species of Hylidae, that occurred throughout both seasons. Stream depth decreased in the dry season, but microhabitat availability remained relatively stable in many streams, and predator density did not change significantly. Tadpoles of three out of the four species studied were more abundant during the dry season, which may be an adaptation to adjust time of metamorphosis to the rainy season. Tadpoles changed their patterns of microhabitat use between seasons, although the potential causing factors investigated did not seem to be responsible. Tadpole plasticity in microhabitat use may indicate the existence of selective pressures that vary through time and space and are still not well understood. [ABSTRACT FROM AUTHOR]

Crypsis results from a complex interaction among prey coloration, background matching, behaviour and predator visual perception. Tadpoles are known to have varied adaptations to escape predation, but the use of crypsis is little explored, although it is likely for certain species. We investigated potential escape mechanisms related to active escape (fleeing) and crypsis improvement in Bokermannohyla alvarengai tadpoles, proposing a new method to measure cryptic potential. We studied the range of distances covered by threatened and fleeing tadpoles and the proportion of tadpoles that seek shelter or remain exposed after fleeing. We hypothesized that tadpoles that remain exposed may use alternative strategies to avoid detection, such as reaching deeper microhabitats or positioning themselves on substrates that confer greater crypsis than the ones they were on before disturbance. A significantly greater proportion of tadpoles remained exposed after disturbance and positioned themselves on backgrounds that offered greater cryptic potential, but did not differ in depth. Tadpoles may respond to a trade-off between sheltering and being cryptic. On the one hand, they may remain close to retreat sites or they may escape to microhabitats that provide appropriate background matching as a means to achieve crypsis. On the other hand, the absence of matching backgrounds in the tadpoles' vicinities may induce them to seek shelter. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 437–446. [ABSTRACT FROM AUTHOR]

Microhabitat use is an important component of anuran behavior in both the tadpole and the adult stages. It is potentially influenced by phylogeny and extant ecological factors acting as selective pressures, such as predation, competition, or physical habitat properties. We aimed to test whether patterns of microhabitat use vary among species, habitats and sites, and how much of this variation can be explained by phylogenetic relatedness. We collected data on microhabitat use at five different sites, where we obtained a total of 4,230 records of individual tadpoles of 34 species in 15 genera and 7 families, and a total of 1,163 records of adult individuals of 39 species in 16 genera and 8 families. Mantel tests conducted to relate species dissimilarities in microhabitat use and phylogenetic relatedness indicated a weak but significant relationship for adult anurans, and no relationship for tadpoles. Our results suggest that microhabitat use is a plastic and variable trait, overcoming phylogenetic signal in tadpoles. In adult anurans, very little of the variation in microhabitat use can be explained by phylogenetic relatedness. Microhabitat use is not a good predictor of phylogeny, but it may be a very interesting subject to study natural selection and adaptation. [ABSTRACT FROM AUTHOR]

We studied the composition and richness of local tadpole assemblages in several streams at forest site in southeastern Brazil. We initially focused on species distributions within streams, comparing the relative availability of microhabitats with the relative use of each microhabitat type by tadpoles of different species, in order to assess the existence of preference patterns. Then we assessed the role of features assumed to influence species distributions among streams, which may influence breeding site selection by adult frogs and, consequently, tadpole distribution. These features were stream size, tadpole predator abundance, structure of marginal vegetation, and microhabitat availability for tadpoles. We looked for gradients of species richness along gradients of the variables noticed to influence tadpole assemblage composition. Tadpoles of all species showed selectivity in microhabitat use. Species distribution among streams was influenced mostly by number of potential tadpole predators present, stream volume, arboreal vegetation cover at stream margins, and tadpole microhabitat diversity, though only the first two variables accounted for gradients in species richness. Even though smaller streams tend to shelter more anuran species than larger ones at sites in southeastern Brazil, we recommend the conservation of streams of a range of sizes and structural features, since anuran assemblages associated with streams vary in species composition along gradients in these characteristics. [ABSTRACT FROM AUTHOR]