Landscape genetics reveal fine-scale boundaries in island populations of Indonesian long-tailed macaques

Human activities directly and indirectly influence the gene flow of wildlife populations, significantly affecting their population structure. On Bali, Indonesia, long-tailed macaque (Macaca fascicularis) populations are associated with relatively undisturbed forest remnants, providing resources for macaques through human worship practices. To evaluate the long-term impact of this anthropogenic landscape on gene flow in macaques, we measured the microsatellite heterozygosity and genetic distance of 15 populations across the island. We then used assignment tests to measure more contemporary movement between populations. We found significant population structure across the island and found that despite this significant structuring, contemporary macaque dispersal across the island is relatively high, with a number of first generation migrants detected. Moreover, we identified one population in the core of the island that acts as a magnet for migrants, receiving 50 % of the first generation migrants in this analysis. Finally, we used individual-level Bayesian clustering analysis combined with kriging techniques to measure fine-scale genetic structure and identify significant boundaries relative to the landscape. Significant genetic structure suggests that the existence of forested temple sites and long-term co-existence with humans may have contributed to relative isolation between populations, even though macaques are known for their high dispersal abilities. However, more recent changes in land use practices in Bali, such as reallocation of lands for tourism, are influencing the patterns of dispersal and increasing the movement of individuals between novel sites, shifting the population structure of the macaques and potentially reducing island-wide genetic diversity.