Abstract:
In vertebrates, reproductive endocrine concentrations are strongly differentiated by sex, with androgen
biases typifying males and estrogen biases typifying females. These sex differences can be reduced in
female-dominant species; however, even the most masculinised of females have less testosterone (T)
than do conspecific males. To test if aggressively dominant, female meerkats (Suricata suricatta) may
be hormonally masculinised, we measured serum androstenedione (A4), T and estradiol (E2) in both
sexes and social classes, during both ‘baseline’ and reproductive events. Relative to resident males,
dominant females had greater A4, equivalent T and greater E2 concentrations. Males, whose endocrine
values did not vary by social status, experienced increased T during reproductive forays, linking T to
sexual behaviour, but not social status. Moreover, substantial E2 concentrations in male meerkats may
facilitate their role as helpers. In females, dominance status and pregnancy magnified the unusual
concentrations of measured sex steroids. Lastly, faecal androgen metabolites replicated the findings
derived from serum, highlighting the female bias in total androgens. Female meerkats are thus strongly
hormonally masculinised, possibly via A4’s bioavailability for conversion to T. These raised androgen
concentrations may explain female aggressiveness in this species and give dominant breeders a
heritable mechanism for their daughters’ competitive edge.
