The role of androgenic steroids in shaping social phenotypes across the lifespan in male marmosets (Callithrix spp.).

Steroid hormones, particularly androgens and their metabolic derivatives, play a prominent role in shaping morphological, behavioral, and social phenotypes in many organisms, including primates. This paper reviews the endocrine correlates of development in male marmoset monkeys of the genus Callithrix (C. kuhlii and C. geoffroyi). A lifespan developmental perspective is adopted, in which our knowledge of hormone effects and profiles from prenatal periods through old age is described. Prenatal steroid hormones appear to play a prominent role in shaping behavioral and morphological phenotypes both the prepartum and in the early postpartum periods of life, with exposure to high gestational androgen associated with reduced fetal growth and lower levels of juvenile play. Early postnatal elevations in androgen levels in males are ubiquitous in Callithrix, and play a role in the further differentiation of male genital morphology and behavior. Changes in androgens as males approach puberty are similar to the conventional primate pattern, and unlike in female marmosets, gonadal steroidogenesis appears to be independent of social context. In adults, androgens appear to be an important modulator of paternal responsiveness to infants, since androgens are low at times when males typically engage in maximal levels of care, and fathers that care for offspring extensively appear to have lower androgen levels than fathers that are less involved in offspring care. Finally, aging in male marmosets is associated with reduced androgen levels. This reduction appears to be attributable to deficits in central mechanisms, since experimental induction and inhibition of gonadal steroid synthesis and release appears to be normal in older males. Together, these results suggest a complex picture of lifetime involvement of androgens in shaping marmoset phenotypes.