Temperature effects on metabolism and energy requirement during the fast growth phase in the red-footed tortoise, Chelonoidis carbonaria.

Abstract

Early life is a challenging phase because of the high rates of morphophysiological development and growth. Changes in ambient temperature, which directly affect energy metabolism and digestive functions in ectotherms, may be of great impact during this phase. We addressed this issue in red-footed tortoise (Chelonoidis carbonaria) hatchlings kept in captivity. To this end, we investigated the effect of temperature (28 °C and 18 °C) on mass-specific gross energy intake (GEI_m), daily body mass gain (MG), daily intake of gross energy (GEI), digestible energy (DEI), resting metabolic rate (RMR), and specific dynamic action (SDA) components during different seasons in the first 13 months after hatching. Greater GEI_m and MG were observed in spring (381.7 ± 84.9 J.g^-0.86.day^-1 and 0.9 ± 0.4 g.day^-1) and summer (356.9 ± 58.9 J.g^-0.86.day^-1 and 1.0 ± 0.4 g.day^-1). The highest and lowest RMRs at 28 °C were observed in spring (36.4 ± 5.1 kJ.kg^-1.day^-1) and winter (22.4 ± 6.2 kJ.kg^-1.day^-1), respectively. Regardless season, hatchlings showed greater GEI and DEI, O₂ consumption, CO₂ production, RMR, maximum metabolic rate after feeding (FMR_MAX), and heat increment (FMR_MAX- RMR) at 28 °C compared to 18 °C. In addition, the significant body mass influence showed allometric exponents of 0.62 at 28 °C and 0.92 at 18 °C for RMR. Our results indicate an important effect of environmental temperature on energy requirements and utilization in C. carbonaria hatchlings, which is seasonally influenced even in this early phase of life.