Temperature has an important effect on amphibians, influencing virtually all physiological systems. Thermoregulation is used to manage unfavourable thermal conditions, but has been poorly studied in aquatic amphibians, and no information is available for adult aquatic anurans. We studied the temperatures to which the Critically Endangered and high Andean fully aquatic Titicaca water frog Telmatobius culeus is exposed and investigated possible thermoregulation strategies of the species in the wild. We measured water temperature in different seasons, microhabitats and depths at which T. culeus is most abundant. We established transects to obtain population densities and activity patterns of the species during the day. Seasonal and daily temperature variations as well as temperature variations among depths and microhabitats were noted. These variations were associated with densities of visible T. culeus, where adult densities were higher at depths with more stable temperatures. T. culeus behaviour associated with thermoregulation strategies in the aquatic habitat included depth selection and movement of individuals between different microhabitats. Selection of microhabitat depended on the temperature at a site and the hour of the day. These results indicate possible behavioural thermoregulation strategies such as movement to different sites or basking used by a highly specialized amphibian, and provide insights into how aquatic benthic organisms use strategies for thermoregulation in aquatic heterogeneous environments. These strategies are probably also used by other aquatic organisms from the tropical Andes. Knowledge of how these organisms respond to temperature could also help to understand the impact of global warming on their status.

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Body nutrient profiles in ecological studies allow for relating the nutritional status of consumers and their effects on the movement and retention of elements in ecosystems, as well as reflecting feeding conditions and habitat quality. This study compared the detailed whole‐body nutrient composition (macronutrients, minerals, fatty acids and amino acids) of two omnivorous natives Orestias killifish from Lake Titicaca (Orestias agassizii and Orestias luteus, Valenciennes), the largest lake in the Andes, as an indirect tool to understand differences in their feeding ecology. Although both species are usually described as omnivorous fish, both have amphipods (Hyalella spp) as their main food source. Our results showed that both killifish had a comparable macronutrient composition, and the mineral concentrations of Mg, P and Ca (reflecting bony structures) differed between them. Many of the saturated fatty acids were significantly lower in O. luteus, and O. agassizii had higher concentrations of cis‐vaccenic acid (18:1n11 (cis)), supporting the idea of a higher algal contribution to the diet of this fish. The lower histidine and higher taurine concentrations in O. agassizii compared with O. luteus (independent of body size) may reflect its ubiquitous behaviour and plasticity. This study shows how whole‐body nutrient analysis can identify differences in feeding ecology and feeding behaviour between related species.

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