Primatologist Michelle Rodrigues posted a cool write-up of our most recent paper on geophagy in saki monkeys on her blog SpiderMonkeyTales. Check it out below!
Saki monkeys are a Neotropical primate found in Amazonia. They are seed predators, which means that rather than ingesting seeds and passing them whole (like spider monkeys), their teeth and digestive system destroy the seeds they eat. This is a good way to get maximum nutrition from those seeds, but the seeds contain high levels of secondary compounds like tannins. Tannins are the bitter, astringent compounds that give coffee, tea, and wine their unique flavors, but high levels of tannins (much higher than we consume), can be toxic. Other Amazonian seed predators, like parrots, eat soil with clay and high cation exchange capacity, both of which neutralize the toxic effects. Seeds eaten by parrots in the same region have tannin levels toxic to most verterbrates. If the Sakis are eating the same seeds, how do they cope with those levels of toxins?
Sakis eat termite mounds, which contains soil, clay, and nutrients. Adams and colleagues tested between two hypotheses: 1) Sakis eat the termite mounds because they provide nutritious minerals (like vitamins), or 2) to help counteract the potentially toxic effects of secondary compounds (like a detox supplement). If the soil they ate from termite mounds contained more micronutrients, that would support the vitamin hypothesis. If the soils contained that have more clay and and cation exchange properties, that would support the detox hypothesis.
They observed how long the monkeys ate termite mounds, which age/sex classes at the termite mounds, if there were termites present. They also collected samples from termite mounds that the Saki fed at, and compared to control soil samples and unvisited termite mounds.
About 2/3 of the termite mounds contained termites, and Sakis did eat termites at the active mounds. However, they fed from both active and inactive termite mounds, all age/sex classes fed on the mounds. Termite mounds did have higher levels of some minerals than topsoil, and those levels were similar in the both the Saki-eaten mounds and univisited mounds. The eaten- and uneaten-termite mounds did not differ in in clay content, but the termite mounds that were eaten had twice the cation exchange capacity. Adams and colleagues conclude that the Sakis are eating the termite mounds primarly because it helps counteract the effect of the tannins, supporting the detox hypothesis.
So basically, Sakis are wisely self-medicating with termite mounds to counteract the effects of their potentially toxic diet!
An important caveat: Adams and colleagues do not use terms like the “vitamin” or “detox” hypothesis–I use these terms only to simply the function of termite-mound eating. Also, humans are not seed predators, so we do not have the same need for detoxing. Most talk of “toxins” in human diets is pseudoscience, and unless you’re eating some strange things that are not suitable for human consumption, you should have no need for detoxing!