| Geophagy, or soil consumption, is a behavior observed across a broad diversity of vertebrate species, yet the factors driving this phenomenon remain elusive. Studies of sympatric species that exhibit significant differences in diet can help elucidate the ecological basis of geophagy. Five distinct hypotheses were tested using sympatric species that may best explain the benefit of soil consumption in primates: antacid relief, plant secondary metabolite (PSM) adsorption, parasite mitigation, alleviation of diarrhea, and nutrient supplementation. I conducted observations of diademed sifakas (Propithecus diadema) and common brown lemurs (Eulemur fulvus) in primary rainforest habitats of Tsinjoarivo, Madagascar. I studied animals of both sexes and multiple age classes from both species during two seasons (June-August and October-November, 2014). I recorded the frequency of plant food and soil consumption and collected plant materials and soils the lemurs consumed, as well as subsequent fecal samples from study subjects. Sampling results were compared to assess whether geophagy was associated with dietary consumption of fruit and/or fiber, and if soil played a role in the level and composition of gastrointestinal parasites encountered. Geophagy did not appear to afford the same function for both species at all times throughout the year. PSM neutralization, parasite mitigation, and nutrient supplementation were the most likely non-exclusive functions. Captive colony managers would do well to provide these species, and likely others, with the opportunity to consume soil as it plays a specific physiological function in the diet and health of primates. |
