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The 5HTTLPR polymorphism in the promoter region of the human serotonin transporter (SLC6A4) gene is known to be associated with various stress-related psychological and psychiatric phenomena. We observed that a similar diallelic polymorphism in the orthologous gene of rhesus macaques (Macaca mulatta) was related to the reproductive life history of 580 males residing in the free-ranging colony of Cayo Santiago, Puerto Rico, between 1985 and 1998. At first glance, the polymorphism appeared to be selectively neutral because no difference in total reproductive output was noted between males of different 5HTTLPR genotypes. However, whereas heterozygotes were significantly more reproductive than homozygotes at intermediate age (10‐13 yr), the opposite held true before and after this period (n 5 682 offspring; randomization P 5 0.014). This association, which explains approximately 7% of the observed variation in sire age, most likely reflects different natal dispersal patterns and represents the first reported instance of a genetic influence on reproductive timing in mammals. behavior, male reproductive timing, male sexual function, neurotransmitters, rhesus macaques, serotonin transporter

Rhesus macaque females regularly copulate with a number of partners, and produce a single offspring per reproductive cycle in over 99% of cases. We used genotyping of 10 STR markers to determine paternity in the Cayo Santiago population of rhesus macaques. About 1,500 monkeys have been analyzed to date, with their marker genotypes entered into a computerized database. These data enable us to report the first documented case in any cercopithecine nonhuman primate species of the production of twin offspring sired by different males.

Gene conversion and balancing selection have been invoked to explain the ubiquitous diversity of the antigen-presenting proteins encoded in the vertebrate major histocompatibility complex (MHC). In the present study, direct evidence for over-dominant selection promoting MHC diversity in primates is provided by the observation that, in a large free-ranging population of rhesus macaques, males heterozygous at MHC class II locus Mamu-DQB1 sired significantly more offspring than homozygotes (the male-specific selection coefficient s equals 0.34). This heterozygote advantage appeared to be independent of the actual male Mamu-DQB1 genotype. No similar effect emerged for a captive group of monkeys of similar genetic background but under veterinary care.

A VNTR polymorphism previously characterized in the promoter region of the human serotonin transporter (SLC6A4) gene was also found to segregate two major alleles (l and s) among the free-ranging rhesus macaques of Cayo Santiago, Puerto Rico. When VNTR genotypes were related to age at male natal dispersal on Cayo Santiago, ss homozygotes (43 of 532 males tested) were found to have left their natal groups significantly earlier (age 57.1 ± 2.6 months) than carriers of the l allele (ll age, 71.5 ± 2.1 months; ls age, 63.5 ± 1.5 months; P = 0.0001). Since migration implies reproductive costs and benefits that change with age at dispersal, migration at an intermediate age might have conferred a heterozygote advantage serving to maintain the VNTR polymorphism via overdominant selection.

Commentary on Cherkas et al. (2004). Genetic Influences on Female Infidelity and Number of Sexual Partners in Humans: A Linkage and Association Study on the Role of the Vasopressin Receptor Gene (AVPR1A). Twin Research, 7, 649–658.

The 5HTTLPR polymorphism in the promoter region of the human serotonin transporter (SLC6A4) gene is known to be associated with various stress-related psychological and psychiatric phenomena. We observed that a similar diallelic polymorphism in the orthologous gene of rhesus macaques (Macaca mulatta) was related to the reproductive life history of 580 males residing in the free-ranging colony of Cayo Santiago, Puerto Rico, between 1985 and 1998. At first glance, the polymorphism appeared to be selectively neutral because no difference in total reproductive output was noted between males of different 5HTTLPR genotypes. However, whereas heterozygotes were significantly more reproductive than homozygotes at intermediate age (10-13 yr), the opposite held true before and after this period (n = 682 offspring; randomization P = 0.014). This association, which explains approximately 7% of the observed variation in sire age, most likely reflects different natal dispersal patterns and represents the first reported instance of a genetic influence on reproductive timing in mammals.

In many mammalian species, male reproductive success appears to climb sharply at young adulthood, form a brief plateau during prime ages, and decline among older animals, a pattern often attributed to reduced physical condition with ageing. However, solid evidence to either substantiate or refute this profile among nonhuman primates is lacking. Here, we combine a decade of genetic analysis of paternity among free-ranging rhesus macaques, Macaca mulatta, with information about body condition in order to evaluate how changes in morphology might govern age-specific reproduction among males. We show that age-specific reproductive success traverses the same life history profile as found in other mammals, but reductions in reproductive output with advanced age were associated with reduced chances of survivorship rather than accompanied by diminished body condition. We demonstrate that variance in male age at onset of reproduction is three times greater than variance in female age at onset of reproduction. We provide the first evidence from primates that age-specific reproductive output among males is not a consequence of age-related changes in body condition, but reflects social and demographic factors.

Rhesus macaque females regularly copulate with a number of partners, and produce a single offspring per reproductive cycle in over 99% of cases. We used genotyping of 10 STR markers to determine paternity in the Cayo Santiago population of rhesus macaques. About 1,500 monkeys have been analyzed to date, with their marker genotypes entered into a computerized database. These data enable us to report the first documented case in any cercopithecine nonhuman primate species of the production of twin offspring sired by different males.

A systematic search was performed for DNA sequence variation in genes regulating neurotransmitter metabolism in rhesus macaque (Macaca mulatta). These genes included dopamine and serotonin receptors and transporters, and tyrosine hydroxylase. A total of 13 single nucleotide polymorphisms in five different genes were identified, namely: DRD1 (-244T->G), q = 0.45; DRD1 (-179C->T), q = 0.19; DRD1 (-127G->A), q = 0.25; DRD1(-11T->G), q = 0.08; DRD1(-81C->T), q = 0.19; DRD3 (248G->A), q= 0.08; DRD3(341G->C), q = 0.11; DRD3(377A->G), q = 0.19; DRD3 (403C->T; A59V), q= 0.11; DRD4(2608G->A), q= 0.48; HTR1D(-506G->T), q = 0.47; HTR1D(-173C->T), q = 0.47; and HTT(340G->A), q = 0.39. The nucleotide positions listed correspond to the human homologs.