Habitat complexity and its use correlate with soil-transmitted helminthiasis in two social groups of Macaca maura (H.R. Schinz, 1825), endangered primates endemic to Sulawesi island, Indonesia

Sulawesi endemic Macaca maura is included in the IUCN Red List as Endangered due to anthropogenic disturbance and fragmentation of its habitat. Residual populations have a scattered distribution in the karst forests of south Sulawesi. Here the dissolution of limestone layers has created a multi-level landscape hardly accessible for ground predators and humans. In this study, we aimed to obtain better knowledge on the ecological flexibility of M. maura in the use of such a complex habitat, and its consequences on health status. Since all data published on M. maura were obtained from a single group (group B), an additional group (G) was habituated to human presence. We analysed 50 vegetation plots (10 × 20 metres) to discriminate structural features in terms of feeding options (e.g. key food species diversity, density and DBH) and anthropogenic disturbance (e.g. human trails and solid litter). We then correlated these data with habitat use and helminth infection. We collected 74 faecal samples from 18 different adult individuals belonging to both groups. Vegetation analysis suggested that there were 2 suitable habitats: a Ground Forest (e.g. higher abundance of key food species) and a Karst Tower Forest (e.g. lower presence of human trails and solid litter). Gastrointestinal investigation revealed a positive correlation between the prevalence of Trichuris sp. and time devoted to ground food-related activities in all individuals (Spearman correlation, rs = 0.665, p = 0.003). Moreover, behavioural data confirmed that group B, the larger study group of the area, spent most of its activity time in the Ground Forest (N group B = 33 ± 1; N group G = 18 ± 1; χ 2 = 134.30, d.f. = 1, p < 0.001). Since resource availability and predation risk can influence foraging decisions and, ultimately, space use, the “group size effect” might explain the significantly higher proportion of time spent by group B in the Ground Forest. Consequently, due to the Trichuris faecal-oral contamination life-cycle, the chance of infecting individuals based on their feeding habits might be described according to the “soil-transmitted helminthiasis hypothesis”