Hormonal and Morphological Aspects of Growth and Sexual Maturation in Wild-Caught Male Vervet Monkeys (Chlorocebus aethiops pygerythrus)

Abstract

Knowledge of baseline changes in testosterone (T) and other androgens is central to both investigations of morphological, physiological, and behavioral correlates of inter-individual variation in the timing and shape of key events and transitions over the life course and questions of the evolution of species-specific schedules of maturation in primates. T represents an important determinant of spermatogenesis in male mammals and plays a central role in the expression of male sexual behavior and the development of secondary sex characteristics. This research integrates hormonal and morphometric methods to determine age-related changes in fecal testosterone (fT) metabolites and morphological markers of sexual maturation, including testicular volume, body mass (measured as BMI), and canine length, over the life course in a cross-sectional sample (n = 56) of wild-caught South African male vervet monkeys (Chlorocebus aethiops pygerythrus). Contrary to expectations of this study, T was not significantly associated with age (p = 0.1316 by ANOVA). However, BMI (p = 0.00022) and testis volume (p = 4.335e-06) were strongly related to age, corresponding to the eruption of the canine teeth at adolescence (3-4 years of age). These results strongly suggest the existence of an adolescent growth spurt in male vervets. An interpretation of activation of the development of these maturational markers in preparation for challenges encountered at reproductive maturity, including dispersal and reproduction, is tentatively adopted here following Jolly and Phillips-Conroy (2003, 2006). However, future longitudinal observations to determine changes within individuals are necessary to provide greater confidence in this interpretation.