Macaque mothers’ preconception testosterone levels relate to dominance and to sex of offspring

There is increasing evidence to support hypotheses that suggest that mammalian females may have some influence over which sex of offspring they conceive. In the search for a mechanism by which this might occur, female testosterone has become a focus of interest. We investigated the relation between level of faecal testosterone in female Barbary macaques, Macaca sylvanus, measured prior to conception, and the subsequent sex of the offspring. We found that macaques bearing male offspring had higher mean preconception testosterone levels than those bearing female offspring. High testosterone levels were also associated with high maternal dominance. Consistent with theories of sex allocation, testosterone has been shown to underpin dominance behaviour and is also likely to be related to good condition. In addition, female testosterone, unlike male testosterone, rises in response to chronic stress, thus providing a pathway whereby environmental stressors might influence sex allocation.