Variation in chewing efficiency of Yakushima Japanese macaque (Macaca fuscata yakui)

Abstract

ObjectivesChewing efficiency plays an important role in the survival and distribution of primates. Yet, little is known about the intra‐specific variation of chewing efficiency. The purpose of this study is to report the pattern of seasonal and regional variation in chewing efficiency among Yakushima Japanese macaques (Macaca fuscata yakui).Materials and MethodsFecal samples of Yakushima Japanese macaques were collected from lowland, highland and summit areas in Yakushima between July 2015 and March 2016 (n = 236). Using sieving analysis, we compared fecal particle size (dMEAN) and proportion of finest particles p(0) between different geographical areas and seasons.ResultsSeasonally, in the lowland zone, there was a non‐significant decrease in dMEAN during spring, while p(0) was significantly higher during summer than it was during winter and spring. Regionally, dMEAN was higher in the summit zone than it was in other areas during autumn, while p(0) was also higher in the summit zone.ConclusionsWhile seasonal variation in dMEAN can be explained by the reported difference in the proportions of food categories in diet between seasons, its influence is mitigated, possibly by the selective feeding of less mechanically challenging parts in each category. Regional variation in dMEAN and p(0) may be the results of bamboo consumption in this area. Combining our data with studies that focus on seasonal and regional variations of food properties or gut microbes might provide a better understanding of the relation between diet, chewing and digestion in Yakushima macaques.

Effects of diet and age–sex class on the fecal particle size of wild Japanese macaques (Macaca fuscata yakui)

“…In comparison with the previous study (He et al, 2020), we found that, in autumn, the fecal particle size in the summit zone was significantly larger than the result in our study group (Umi-C) Comparison with a previous study on Japanese macaques in Yakushima. The data of the lowland, the highland, and the summit habitat came from a previous study (He et al, 2020). *** p < 0.0005 summit vs. this study, Z = 4.54, p < 0.0005; Figure 5b).…”

“…It remains unknown whether similar correlations exist in other less dietary specialized species. Japanese macaques (Macaca fuscata yakui) that relied on a potentially tough bamboo-dominant diet indeed had larger fecal particle sizes compared to their conspecifics that consumed a different diet (He et al, 2020). However, dietary toughness was not measured in that study.…”

“…Previous studies have found that several factors affect fecal particle sizes in different primate species, such as diet composition (Thiry et al, 2018;Weary et al, 2017), dietary toughness and age (Venkataraman et al, 2014), and re-mastication (Matsuda et al, 2014). However, some of these factors only pertained to species with a highly specialized lifestyle (Matsuda et al, 2014;Venkataraman et al, 2014), while the determinants of fecal particle size remain unclear in other species (He et al, 2020). These results indicate that the role of ecological factors in the determination of fecal particle size warrants further investigation.…”

“…Other particles on each sieve were transferred onto a pre-weighed tinfoil dish and desiccated at 103°C in a vacuum oven for 24 h. After cooling to room temperature in the desiccator, we weighed samples using an analytical balance with a measuring accuracy of 0.0001 g (Shimadzu Libror AEG-220; Shimadzu Scientific Instruments). A previous study of Japanese macaques in Yakushima reported fecal particle size data in the lowland zone in all seasons, as well as data in the highland zone and the summit zone in summer and autumn (He et al, 2020). We used the fecal particle size data from that study for comparison.…”

“…These variations make M. fuscata yakui a suitable model for investigating fecal particle size differences at the intraspecific level. The previous study of Japanese macaques in Yakushima found larger fecal particle sizes in the summit zone compared to the lowland in autumn and speculated that dietary composition and toughness were the causes (He et al, 2020). However, that speculation was based on fecal content analysis, which cannot assess diet composition in detail.…”