https://studyfinds.org/sloths-metabolic-limits-climate/
SWANSEA, United Kingdom — In the lush rainforests of Central and South America, sloths have perfected the art of energy conservation. These slow-moving mammals have evolved to exist on an extremely low-calorie diet, operating within a finely tuned energy budget where minimal expenditure is linked to minimal energy intake. But as our planet warms, this balance may be disrupted, potentially pushing some sloth populations to their metabolic limits.
A study led by Rebecca N. Cliffe and her colleagues from the Sloth Conservation Foundation and Swansea University has revealed that climate change could have profound implications for the survival of sloth populations, particularly those living in high-altitude regions. The research, published in PeerJ, demonstrates that sloths from different altitudes respond differently to temperature changes, with highland sloths potentially facing an uncertain future in a warming world.
Sloths are known for their incredibly slow metabolism, which is about 39% lower than what would be expected for a mammal of their size, according to general mammalian predictions. This adaptation allows them to subsist on a diet of low-nutrient leaves, but it also means they have little energy to spare. Sloths are presumed to exist within a narrow and finely tuned energy budget, which, combined with their limited ability to move to new areas, means that even small changes in temperature could have significant impacts on their survival.
The research team focused on two-fingered sloths (Choloepus hoffmanni) from both lowland and highland areas in Costa Rica. They measured the sloths’ oxygen consumption and body temperature when exposed to different ambient temperatures, ranging from 18°C to 34°C (64°F to 93°F). They also tracked changes in body temperature and posture over several days in response to natural temperature fluctuations.
What they discovered was surprising. While all sloths showed similar responses to temperature changes at the lower end of the scale, their reactions diverged significantly as temperatures rose above 32°C (90°F). Lowland sloths demonstrated an ability to depress their metabolism in response to high temperatures, effectively reducing their energy expenditure and body temperature. Highland sloths, however, lacked this capability. Instead, their metabolic rates continued to increase as temperatures rose, potentially pushing them into an unsustainable energy deficit.
