Prenatal androgen exposure (PAE) plays a pivotal role in masculinizing the developing body and brain, and extreme exposure may contribute to autism, anxiety disorder and schizophrenia. One commonly used biomarker for PAE is the pointer-to-ring-finger digit length (2D:4D) ratio. Although this biomarker is widely used in human studies, relatively few studies have investigated 2D:4D ratio in nonhuman primates, particularly rhesus macaques (Macaca mulatta), one of the most commonly used animals in biomedical research. Thus far, data suggest that sexual dimorphism in 2D:4D ratio may be in the opposite direction in some monkey species, when compared to the pattern exhibited by humans and great apes. Using a large sample size, we investigated whether rhesus monkeys’ 2D:4D ratio shows the same sex-differentiated pattern present in other Old World monkey species. We also investigated whether individual differences in 2D:4D ratio are associated with the social dominance rank of subjects’ mothers during pregnancy, and the social dominance rank the subjects attained as adults. Subjects were 335 rhesus monkeys between 3 years and 24 years of age (M = 6.6). Maternal dominance rank during pregnancy and subjects’ adult dominance rank were categorized into tertiles (high, middle and low). Results showed that, across both hands, male rhesus monkeys exhibited higher 2D:4D ratio than females, a pattern consistent with other monkey species and a reversal from the pattern typically observed in humans and apes. This sex difference was modulated by maternal dominance rank, with female offspring of high-ranking and middle-ranking mothers exhibiting masculinized 2D:4D ratio, indicating that maternal dominance rank during pregnancy may influence levels of PAE. There was no association between subjects’ 2D:4D ratio and the social dominance rank they attained as adults. These findings show a consistent sex difference in Old World monkeys’ 2D:4D ratio that diverges from the pattern observed in apes and humans, and suggest maternal social dominance rank modulates PAE in rhesus monkeys.
Prenatal androgens and estrogens organize the course of body and brain development, contributing to lasting sex differences in brain structure and behavior (Ehrhardt & Meyer-Bahlburg, 1979; MacLusky & Naftolin, 1981). Although prenatal androgens are produced primarily by the testes of the male fetus and are principal hormones that masculinize male genitalia and body morphology (Hughes, 2001), both male and female fetuses experience prenatal androgen exposure from secondary sources. For example, some androgens are produced as byproducts when other steroids are synthesized, and some androgens may originate from the mother (see Knickmeyer & Baron-Cohen, 2006). Although these levels of androgen exposure are typically not high enough to lead to virilization of females' genitalia, they could lead to individual differences within females. Prenatal estrogens are also produced endogenously by both
This longitudinal study spans two generations of rhesus monkeys. First, the study investigates the effects of early rearing experiences on the maternal behavior of first-generation mothers (rates of premature infant rejection) and, second, the study investigates the effects of maternal rejection on the behavior of secondgeneration infants. Rhesus macaque mother-infant dyads (Macaca mulatta-N = 176
Teenage alcohol abuse is a major health concern, particularly because the majority of alcohol consumed by teenagers is via binge drinking, a known risk factor for increasing the likelihood for the development of future alcohol use disorders (AUDs). Identifying individuals at risk for excessive alcohol intake in adolescence is a step toward developing effective preventative measures and intervention programs. As adults with AUDs tend to self-medicate their anxiety with alcohol, this longitudinal study assesses the role of infant anxiety-like temperament in the development of adolescent alcohol abuse using a nonhuman primate model. From birth until they were 5 months of age, behaviors of 64 rhesus monkeys (Macaca mulatta) were coded twice a week using an objective mother-infant scoring system that included behaviors traditionally used to assess anxiety and fearfulness in rhesus monkeys. When subjects were four months old, plasma cortisol was obtained. When subjects were adolescents (M age = 44.88 months), another plasma cortisol sample was obtained about one month prior to allowing them unfettered access to an 8.4% (v/v) aspartamesweetened alcohol solution for one hour a day over five-to-seven weeks. Results showed that behavioral indications of anxiety-like temperament in infancy, including high levels of mother-infant mutual ventral contact, low levels of environmental exploration, and low levels of interactions with peers were predictive of high adolescent alcohol intake (ie, drinking to intoxication).
Attempts to describe the latent structure of human infant temperament have led some to suggest the existence of three major dimensions. An earlier exploratory factor analysis (EFA) supported a triadic structure of temperament in week-old rhesus monkey infants, paralleling the structure in human infants. This study sought to con
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