CONICET | Buscador de Institutos y Recursos Humanos

Ectotherm species are not capable of generating metabolic heat; therefore, they present diﬀerent strategies for regulating their body temperatures, ranging from a precise degree of thermoregulation to a passive thermoconformity with ambient temperatures. In reptiles, aerial basking is the most common mechanism for gaining heat. However, among aquatic reptiles, such as freshwater turtles, aquatic basking is also frequent. Hydromedusa tectifera is a turtle of exclusively aquatic and nocturnal habits widely distributed in South America. We studied the relationship between body temperature (Tb) of H. tectifera and its habitat, and explored the eﬀects of sex, life stage and body size and mass on Tb. Fieldwork was conducted in two streams of a mountain area of central Argentina. We recorded cloacal temperature, size and mass of 84 turtles. We also determined individuals? sex and life stage (adult/juvenile). Regarding ambient temperatures, we measured water temperature on the surface (Tsurf) and at depth of turtle capture (Tdepth) and air temperature. Mean Tb was 18.58 °C (Min = 10.20 °C; Max= 25.70 °C). Tsurf and Tdepth were highly correlated. Multi-model analysis using Akaike criterion indicated that Tb was strongly associated with water temperature, whereas air temperature and body size and mass did notshow a signiﬁcant eﬀect. There was also no eﬀect of turtle sex or life stage on Tb. Our results indicate that H.tectifera is a thermoconformer and eurythermal species. A nocturnal pattern of activity and a fully aquatic lifestyle are suggested as determinant factors.