The common tenrec (Tenrec ecaudatus) just may be a living representative of ancestral placental mammals and they are very interesting when it comes to body temperature regulation and torpor. Torpor is a complex series of physiological changes that reduce an animal’s physical activity as well as heart, breathing and metabolic rates, which also results in decreases in body temperature than can be as low as their surrounding environment. Many mammalian heterotherms undergo hibernation marked by periodic arousals during which time they return to normal body temperature and metabolism, which allows them to get rid of wastes, consume foods, and restore immune function. Tenrecs, on the other hand, hibernate for periods up to 9 months without arousals and have flexible metabolic rates and body temperatures often below 35°C. In fact, observations have shown that the animals may be either active or in torpor in environmental conditions ranging from 12-28°C. While it is to be expected that torpid animals have body temperatures approaching that of the environment, researchers were surprised to see that active animals also had body temperatures within 1°C of the environment. In fact, the metabolic rates of active cold animals were similar to torpid animals. In a new study published in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology, researchers were interested in figuring out what makes tenrecs so unique as that may help us understand how endothermy evolved.
By comparing animals that maintained stable body temperatures of about 32°C with those that were in torpor and had temperatures around 14°C, they discovered that the torpid animals and cold but active animals had more variations in proteins compared to warm animals that showed less variation. In addition, 50.9% of the liver proteins were different between active and torpid animals. Their findings showed changes in genes related to fasting that are typically seen in other mammals such as decreases in genes related to metabolism and the use of metabolic processes that require oxygen in addition to increases in the production of ketones. They also found that the lack of periodic arousals may prevent tenrecs from resetting their homeostasis like other hibernating mammals, which may result in errors that reduce their survival. This may explain why the animals have such large litters (up to 32 young!!).
Khudyakov JI, Treat MD, Shanafelt MC, Deyarmin JS, Neely BA, van Breukelen F. The liver proteome response to torpor in a basoendothermic mammal, Tenrec ecaudatus, provides insights into evolution of homeothermy. American Journal of Physiology – Regulatory, Integrative and Comparative Physiology. In Press.