Male reproductive timing in Rhesus macaques is influenced by the 5HTTLPR promoter polymorphism of the serotonin transporter gene

The 5HTTLPR polymorphism in the promoter region of the human serotonin transporter (SLC6A4) gene is known to be as-sociated with various stress-related psychological and psychiat-ric phenomena. We observed that a similar diallelic polymor-phism in the orthologous gene of rhesus macaques (Macaca mu-latta) 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 sig-nificantly more reproductive than homozygotes at intermediate age (10–13 yr), the opposite held true before and after this pe-riod (n 5 682 offspring; randomization P 5 0.014). This asso