Natal dispersal in rhesus macaques is related to serotonin transporter gene promoter variation

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.