Leaf swallowing and parasite expulsion in Khao Yai white‐handed gibbons (Hylobates lar), the first report in an Asian ape species

Abstract

Leaf swallowing behavior, known as a form of self-medication for the control of nematode and tapeworm infection, occurs widely in all the African great apes (Pan troglodytes schweinfurthii, P. t. troglodytes, P. t. verus, P. t. vellerosus, Pan paniscus, Gorilla gorilla graueri), except mountain gorillas. It is also reported to occur in a similar context across a wide array of other animal taxa including, domestic dogs, wolves, brown bears, and civets. Despite long-term research on Asian great and small apes, this is the first report of leaf swallowing in an Asian species, the white-handed gibbon (Hylobates lar) in Khao Yai National Park, central Thailand. We present the first evidence of leaf swallowing (Gironniera nervosa Planch CANNABACEA) behavior (N = 5 cases) and parasite (Streptopharagus pigmentatus) expulsion (N = 4 cases), recorded during 4,300 hr of direct animal observations during two distinct research projects. We recovered 4-18 rough, hairy, and hispid surfaced leaves from each sample, undigested and folded, from the freshly evacuated feces of five different individuals (2 males, 3 females, 5 to 34+ years old) living in three different social groups, between the hours of 06:00 to 10:30. Based on close inspection of the leaves, as observed in chimpanzees, it was clear that they were taken into the mouth, one at a time, folded and detached from the stem with the teeth before swallowing them whole. All instances occurred during the rainy season, the time when nematode worms were also found in the feces, although they were not found together with leaves in the same feces. These striking similarities in the details of leaf swallowing between white-handed gibbons and African great apes, and other animal species, suggest a similar self-medicative function.

Gastrointestinal parasite infections and self-medication in wild chimpanzees surviving in degraded forest fragments within an agricultural landscape mosaic in Uganda

“…Additional unknown factors may be involved, warranting further investigation. An understanding of the reasons behind the unusually high frequency of leaf swallowing at this site, may lead to a broader understanding of the behaviour in great apes and indeed other species that also exhibit this behaviour [ 99 – 101 ].…”

Host Cognition and Parasitism in Birds: A Review of the Main Mechanisms

“…Chimpanzees, for example, chew the piths of Vernonia amygdalina and swallow Aspilia leaves, which are thought to facilitate the expulsion of intestinal nematodes and cestodes (Huffman, 2001). Gibbons in Thailand are also thought to use Gironniera nervosa leaves for similar purposes (Barelli and Huffman, 2017). A recent comparative analysis found that primate species with a larger absolute brain are more likely to self-medicate, suggesting that self-medication is, to some degree, cognitively demanding (Neco et al, 2019).…”

Self‐medication in nonhuman primates: A systematic evaluation of the possible function of the use of medicinal plants

“…Moreover, alive and motile parasites or parasite fragments have been found trapped or attached to the leaves' surface in the dung after some hours of leaf‐swallowing (e.g., nematode Oesophagostomum stephanostomum , Huffman et al, 1996; tapeworm Bertiella studeri , Wrangham, 1995). Recently, leaf‐swallowing and parasite expulsion ( Streptopharagus pigmentatus ) was reported for the first time in an Asian ape species, the gibbon ( Hylobates lar , Barelli & Huffman, 2016). This suggests that this adaptive self‐medicative behavior is not restricted to African great apes and might occur more widely than previously found.…”

“…More often than not, direct or indirect observations of self‐medication in primates are not the specific focus of research, but unexpected events during field data collection (Huashuayo‐Llamocca & Heymann, 2017; Morrogh‐Bernard et al, 2017; Wrangham, 1995; Wrangham & Nishida, 1993). Therefore, more focused efforts and research on long‐term study sites with well‐habituated primate groups are important sites for future systematic investigations of self‐medication (e.g., Barelli & Huffman, 2016). Furthermore, besides a systematic and intensive sample collection, researchers from different research areas, such as ethnobotany, behavioral ecology, primatology, and pharmacology, should collaborate and integrate their field and laboratory research in future multidisciplinary studies to further advance this topic.…”