Sperm concentration, coagulum weight, and testosterone levels differences according to social rank in male stump-tail macaques (Macaca arctoides)

摘要

In multi-female multi-male group-living species, both sexes can copulate with diverse partners. According to the priority of access model, high-ranking males have higher access to females during their fertile phases than the lower-ranking competitors. However, when females' ovarian cycles are synchronized, dominant males are unable to monopolize all females, which gives a chance to lower ranking males to sporadically copulate and increase their likelihood to fertilize a female. Therefore, subordinate males perhaps show physiological characteristics allowing them to contend with the advantage that the dominant males already have. It was investigated if sperm counts, weight of the seminal coagulum, and testosterone levels showed any differences according to their social rank in male stump-tailed macaques. Testosterone levels increased linearly in relation to social rank (P = 0.004). No evidence was found that in the first ejaculation dominant rank was positively related to sperm counts and weight of the seminal coagulum. In the second ejaculation a positive correlation between dominant rank and sperm counts and weight of the seminal coagulum was found (P & 0.001). By the third ejaculation there was a negative correlation between sperm counts and dominant rank (P & 0.001), but no variability in the weight of the seminal coagulum. The results showed that high-rank is related to better physiological conditions to sustain multiple ejaculations, thanks to having higher testosterone levels. (C) 2018 Elsevier Inc. All rights reserved.