As our planet continues to warm, the fate of these iconic creatures hangs in the balance. The sloth's strategy of extreme energy conservation, which has served them well for millions of years, may prove to be a liability in a rapidly changing world. Yet, by understanding these vulnerabilities, conservationists hope to develop strategies to protect these unique animals.
The researchers used a technique called indirect calorimetry to measure the oxygen consumption of 12 adult two-fingered sloths. The animals were placed in a metabolic chamber where the temperature could be controlled. Oxygen consumption was measured using an open-flow system, which involves pumping fresh air into the chamber and analyzing the air that comes out.
By measuring the difference in oxygen concentration between the incoming and outgoing air, the researchers could calculate how much oxygen the sloths were using, which is directly related to their metabolic rate. Body temperature was measured using small temperature loggers inserted rectally. The researchers also observed the sloths' posture in response to temperature changes.
The study found that sloths have a metabolic rate about 39% lower than expected for mammals of their size. Both highland and lowland sloths showed similar responses to temperature changes up to about 32°C. Above this temperature, lowland sloths were able to decrease their metabolic rate while highland sloths' metabolic rates continued to increase.
Highland sloths consistently had higher body temperatures than lowland sloths. When modeling the effects of a 2°C increase in ambient temperature due to climate change, the researchers predicted that lowland sloths' body temperature would increase by 2.13°C, while highland sloths' would increase by 1.53°C. However, the continuing increase in metabolic rate for highland sloths could make this temperature rise more problematic for them.
The study had several limitations. The sample size was relatively small, with only 12 sloths used for metabolic measurements and even fewer (3) highland sloths. All sloths were captive animals, which might not perfectly represent wild populations. The temperature changes in the metabolic chamber were relatively rapid, which might not accurately reflect gradual climate change. The model predicting the effects of climate change is simplistic and doesn't account for potential adaptations over time or other environmental factors that might influence sloth metabolism and survival.
The key takeaway from this study is that highland and lowland sloth populations may respond differently to climate change, with highland sloths potentially being more vulnerable. This highlights the importance of considering population-specific adaptations in conservation planning. The study also underscores the unique metabolic adaptations of sloths and how these might interact with climate change.
The researchers suggest that the limited ability of sloths to increase their energy intake might make it difficult for them to cope with increased metabolic demands from higher temperatures. This study provides important insights for sloth conservation and illustrates how climate change can have complex and varied effects on different populations of the same species.
This research was funded by donations to an Indiegogo crowdfunding campaign and the Sloth Conservation Foundation. The authors declared no competing interests. The study was approved by the Swansea University Animal Welfare & Ethical Review Process Group and the Costa Rican government.