Socio-ecological studies of the wild stump-tailed macaques in Thailand: What we have discovered and prospects for the future

The stump-tailed macaque, Macaca arctoides, is the most distinctive of its genus in terms of reproductive anatomy and behavior. The ultimate challenge is to clarify why unique reproductive traits have evolved in this species. Although there have been some previous studies of sexual behavior in this species, the animals studied were born in captivity or reared in laboratory conditions that do not reflect their natural environment. Because very few ecological and ethological studies have been conducted under natural conditions, there is still a lack of knowledge about this species. This was the starting point for this study. As the main outcome of this study, long-term behavioral observations were conducted with a wild population of stump-tailed macaques, and the mating strategies of the males were analyzed based on behavioral data. In parallel with this behavioral study, my colleagues and I conducted paternity tests using 10 microsatellite DNA markers on DNA samples collected using our newly developed non-invasive sampling method. The results of the paternity tests will be compared with the behavioral data to determine whether the mating strategies of the males have provided them with reproductive success. In the process of comparing mating strategies and reproductive success, a number of ancillary results were obtained, including a discussion of the unique facial expressions seen during copulating and the function of copulation calls by males. In this article, I describe and organize the background of each of these results and provide future perspectives.