Inter- and intraspecific sexual behavior in two species of macaque: A possible behavioral barrier to gene flow

Adult male pigtail and rhesus monkeys have longer latencies for sexual responding to females of the other species than to females of their own species. Further, males of both species show testosterone rises when introduced to new conspecific females, but neither showed hormonal rises when introduced to extraspecific females. The rhesus males during the nonbreeding season for rhesus showed neither a hormonal rise nor any sexual behavior when introduced to cycling and receptive pigtail females. These data are used to argue that whereas cogeneric females may have some similarities with conspecific females, males are less attracted to them. Initial agonistic responses might preclude the long association requisite for the development of sexual behavior between extraspecific macaques and thus serve as a behavioral barrier to gene flow among sympatric macaques, which are physiologically freely interfertile.