Exceptional endocrine profiles characterise the meerkat: sex, status, and reproductive patterns

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.

Androgens predict parasitism in female meerkats: a new perspective on a classic trade-off

“…Consistent with a prior report [12], dominant females had significantly greater FAM concentrations than did subordinate females (electronic supplementary material). The females' log FAM concentrations (x 2 (1) ¼ 12.97, p , 0.001),…”

“…We conducted this study on a previously described, wellhabituated, wild population of meerkats living in the Kuruman River Reserve in South Africa's Kalahari Desert [12][13][14][15][16][17][18]. Our focal subjects, from 12 clans (or groups), were 37 sexually mature female meerkats (11 dominant, 25 subordinate and 1 that achieved dominant status during the study and is represented in both social classes).…”

“…Following extraction, we analysed FAM via enzyme immunoassay, using previously validated methods [12,17]. We analysed samples in duplicate (re-analysing those for which coefficients of variation exceeded 10%).…”

“…concentrations in female meerkats (Suricata suricatta)-a species in which all females naturally experience raised androstenedione and T [12]-relate to parasite loads in a manner similar to that experienced by many males [4][5][6][7][8].…”

“…Although subordinate females show some degree of hormonal 'masculinization,' the dominant female has significantly greater concentrations of total androgen than does any other group member [12], which may enable her to restrict the development and reproduction of potential rivals [14,15]. Dominance status dramatically increases reproductive success, but can also incur immunosuppressive costs, as evidenced by increased parasitism [16].…”