Dialium seed coprophagy in wild western gorillas: Multiple nutritional benefits and toxicity reduction hypotheses

Abstract

Unraveling the relationship between the unusual feeding behaviors and the nutritional intake of endangered species may provide crucial information for understanding species response to habitat unpredictable changes. Primates occasionally re-ingest fruit seeds alongside ingestion of feces, a behavior called coprophagy. The nutritional benefit is one of the several non-mutual exclusive hypotheses proposed to explain this behavior. We investigated the ecological correlates of coprophagy in wild western gorillas. We tested whether coprophagy occurred during periods of lower fruit availability and whether it led to higher nutrient intake in comparison to the other food. Data integrated phenological, fecal and nutritional analyses of gorilla food with behavioral observations collected at two sites in Central Africa (Mbeli Bai: ad libitum observations on 15 groups/solitary males, October 2002-November 2005; Bai Hokou: 5-min scan on a habituated group, December 2004-December 2005). Coprophagy occurred at the end of the high-fruiting season in association of two Dialium species. Coprophagy correlated positively with the occurrence of Dialium spp. fruit in gorilla feces and in the feeding scans, and showed a positive trend with Dialium availability but not with total fruit availability. Nutritional comparison of Dialium seeds with other important gorilla food showed higher fat and mineral content, particularly of Mg, but also of phenols and tannins in Dialium seeds. We discuss how the effect of gut processing and gut heat via coprophagy may act as cooking-like effect: increasing the ability to maximize nutrient intake by concurrently softening fibers and decreasing the toxic effect of antifeedants, like in human traditional cooking. Our results support both the multiple nutritional benefit hypothesis and the toxicity reduction hypothesis. Since Dialium is precious timber, the importance of this tree for the critically endangered western gorillas should be taken with high consideration when planning controlled logging of degraded forests or in face of habitat changes.

The distribution of plant consumption traits across habitat types and the patterns of fruit availability suggest a mechanism of coexistence of two sympatric frugivorous mammals

“…However, the high consumption of Dialium spp. fruits in the dry season, when fruit availability is low, was also observed by Masi and Breuer () in the Republic of Congo and in the Central African Republic.…”

What, where and when: spatial foraging decisions in primates

“…For example, folivorous primates' resources are more homogeneously distributed and are present throughout the year (and are therefore easily accessible) than are resources of fruit specialists (e.g. Chapman, White & Wrangham, 1994;Chapman, Wrangham & Chapman, 1995;Sayers, 2013;Masi et al, 2015;Masi & Breuer, 2018).…”

Divergent strategies in faeces avoidance between two cercopithecoid primates

“…This group of animals has a popularized reputation for being rather liberal when it comes to their disposition towards faeces, owing to the many anecdotal reports of coprophagy, throwing faeces and even 'painting' their enclosure walls or other substrates with faeces [20,21]. Many such observations were made at captive facilities and are regarded as being abnormal or pathological signs of distress [21], but even in nature, chimpanzees (Pan troglodytes), bonobos (P. paniscus) and gorillas (Gorilla gorilla) may reingest undigested seeds from their own faeces [22][23][24][25]. Importantly, however, these behaviours usually concern their own waste products, which pose significantly fewer risks of encountering novel parasites.…”