Mycophagy in primates of the Issa valley, Tanzania

Mycophagy (fungi consumption) is an important animal-ecosystem interaction and provides nutrients for numerous mammalian taxa, such as primates. Although mushroom consumption is a widespread behaviour in about a quarter of all known primate species, surprisingly little is known about their use of mushrooms as either a staple or fallback food, and the relationship between mushroom availability and consumption. We used direct observational data on mushroom consumption in the diet of three sympatric primate species: Chimpanzees (Pan troglodytes schweinfurthii) and Red-tailed monkeys (Cercopithecus ascanius) from 2019-2022, and yellow baboons (Papio cynocephalus) from 2015-2022 in a mosaic woodland habitat in the Issa valley, western Tanzania, to address these gaps. We analysed mushroom consumption patterns and assessed mushroom availability from line transects for a period of 15 months (Oct 2022 – Dec 2023). Our findings show that mushrooms were a consistent dietary component for all three species during the wet season (October-April; chimpanzees – 4 %, baboons – 17 %, and red-tailed monkeys – 4 %), while baboons also continued to consume mushrooms (> 10 % of their annual diet) even when availability was low outside the wet season. This is also the first report of mushroom consumption by a red-tailed monkey. We conclude that mushrooms serve as a fallback resource for Issa chimpanzees and red-tailed monkeys, while they represent a preferred food for Issa baboons. We contextualise mushroom consumption as a potential strategy of niche partitioning to reduce interspecific feeding competition as well as underscore the importance of mycophagy and its role in primate dietary ecology and human evolution.