Metabolic Depression in Estivating Long-Neck Turtles (Chelodina rugosa)

Long-neck turtles, Chelodina rugosa, inhabit seasonally ephemeral water holes on the coastal floodplains of the wet-dry tropics of Australia. Late in the annual dry season, the turtles bury themselves in the drying mud and estivate for as long as 4-5 mo until the wet season rains begin. We measured the oxygen consumption of five turtles that were induced to estivate in containers of mud at 30° C. This was typical of soil temperatures measured in natural estivation sites. The metabolic measurements of estivating turtles were compared to the standard metabolic rates (SMRs) at 30° C of these five postestivation turtles after they had spent 36 h in water and to the SMRs of 10 preestivation turtles. There was no difference between the pre- and postestivation SMRs, but the metabolic rates of estivating turtles decreased over about 2 wk to 28% of the SMR. This was not a response to starvation, because postestivation turtles were not fed. This metabolic depression conserves energy and, presumably, water during estivation, which lengthens the time the turtles can survive the dry conditions and allows them to emerge from estivation with more resources for growth and reproduction.