Sloths, known for taking life very calmly, are among the slowest land animals in the world. Specifically, the three-toed sloth (Bradypus tridactylus ) is the laziest sloth of all, as it barely travels about two meters per minute and, only in the case of being threatened by a predator, can it ‘run’ at about 7 , 5 cm per second (and he is already looking for speed).
It is surprising how this idling life form may have been evolutionarily selected up to the present day. However, it seems that this very slowness is the reason for its evolutionary success. It turns out that their slow metabolism allows them to survive only by feeding on plant species with little energy value, such as the ceiba ( Ceiba pentandra ) and yagrumo ( Cecropia peltata ) leaves. Of course, how could it be different, digesting them also takes time and digestions of up to 50 days have been recorded, often discomfort!
Fortunately or unfortunately, animals are open energy systems and after the matter and energy that we acquire from the environment undergoes a transformation, one part of them is used and the other is expelled outside. In the case of sloths, this process usually happens once a week (like when some humans go on vacation). When it comes to going to the bathroom, everything gets complicated, since this is the only time when they abandon life in the heights and come down from the trees to defecate and urinate. This situation puts them in serious danger, since for a long time they are exposed to predators such as anacondas, jaguars and ocelots.
But, why expose yourself to these dangers and not defecate from above, as most arboreal animals do? The answer is still a mystery to science. There are several hypotheses, some of them criticized by the latest work by Julian Monge-Najera, a researcher at the Distance State University of Costa Rica, and published in the UNED Research Notebooks in 2021. In his study, Monge-Najera rejects symbiotic theories such as fertilization of trees with feces; communication between individuals through chemical messages; obtaining nutrients from the soil, as the claws get dirty and lick them afterwards; and increasing populations of moths, which grow in their buried feces. The scientist rejects them all for lack of experimental support and contradictions in the scientific literature itself. Finally, Monge-Najera proposes a new theory in which he refers to natural selection , saying that, since the extinct ancestors of sloths were exclusively terrestrial, there has not been enough selective pressure for current species to leave the ground to defecate. . If true, it could be that the sloths did not take as much risk as they seem when coming down from the heights.
References:
Monge Nájera, J. (2021). Why sloths defecate on the ground: rejection of the mutualistic model. UNED Research Journal, 13 (1), 4. https://doi.org/10.22458/urj.v13i1.3438
