Wood and meat as complementary sources of sodium for Kanyawara chimpanzees (Pan troglodytes)

Abstract

Objectives: Sodium, a vital micronutrient that is often in scarce supply for tropical herbivores, is sometimes found at high concentration in decaying wood. We tested two hypotheses for chimpanzees: first, that wood-eating facilitates acquisition of sodium; second, that wood-eating occurs in response to the low availability of sodium from other dietary sources. Materials and Methods:We studied the behavior of more than 50 chimpanzees of all age-sex classes in the Kanyawara community of Kibale National Park, Uganda. We quantified the sodium content of dietary items, including wood samples from tree species that chimpanzees consumed or did not consume. To assess variation in sodium intake, we used 7 years of data on time spent feeding on plant foods, 18 months of data on rates of food intake by adult females, and 20 years of data on meat-eating.Results: Major dietary sources of sodium were wood, fruits and meat. Chimpanzees consumed wood primarily from decaying trees of Neoboutonia macrocalyx (Euphorbiaceae), which had substantially higher sodium content than all other dietary items tested. Wood-eating was negatively correlated with fruit-eating. Females ate wood more often than males, while males had a greater probability of consuming meat at predation events.Discussion: We propose that females ate wood more often than males because females had reduced access to meat, their preferred source of sodium. This hypothesis suggests that the need for sodium is a motivating reason for chimpanzees to consume both meat and wood. K E Y W O R D S dietary salt, Kibale National Park, meat-eating, nutritional ecology, sex differences

The impact of excessive salt intake on human health

“…Whether this salt intakelow by contemporary standards imposed sufficient selection pressure to retain evolved salt appetite is uncertain. On the one hand, chimpanzees retain salt-seeking behaviours when environmental sodium is low 84 and salt-craving is reported in humans with salt-wasting disorders such as Gitelman Syndrome 85 and adrenal insufficiency 86 , including a classical case report of a child who consumed salt in mineral form 87 . On the other hands, salt craving is not a consistent feature of saltwasting disorders and controlled experiments that induce salt-depletion in healthy people do not provide evidence of an innate salt appetite 88 .…”

Contrasting biodiversity and food web structure of three temporary freshwater habitats in a tropical biodiversity hotspot

“…In the dry season, tree holes provide water when other shallow water bodies do not contain water any more. Based on information in the present study, it is plausible that higher concentrations of salts accumulating in tree holes from rain‐washed Sahara dust could be an additional contributing factor, as it may be a way for chimpanzees to consume salts that are not readily available in this area, located far from the nearest ocean (Reynolds et al, 2009; Reynolds et al, 2015; Rutering et al, 2020). There are distinct threats for each habitat type.…”

Wild Chimpanzee Welfare: A Focus on Nutrition, Foraging and Health to Inform Great Ape Welfare in the Wild and in Captivity

“…There has been a growing amount of research on non-fruit food items rich in microminerals. Foods such as insects [ 32 , 41 ], crustaceans [ 55 ], pith [ 56 ], soil [ 57 ], and decaying wood/bark [ 58 , 59 ] contain essential microminerals, including calcium, phosphorous, magnesium, potassium, sodium, chlorine, sulfur, iron, zinc, copper, manganese, iodine, cobalt, selenium, and chromium because research on captive nonhuman primates found that they are imperative for physiological processes [ 48 ]. In a wild community, at Budongo Forest in Uganda, a micromineral consumption summary reported chimpanzee ( P.t.…”

“…Some food items with considerable amounts of sodium are animal prey and ripe fruits [ 20 , 32 , 37 ], followed by pith and decaying wood [ 56 , 58 , 59 ]. Sodium is essential in maintaining and regulating water intake in the body and iron is essential for transferring oxygen in the circulatory system.…”