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. 2016 Oct 18:6:35492.
doi: 10.1038/srep35492.

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

Charli S Davies  1   2 , Kendra N Smyth  1   2   3 , Lydia K Greene  1   2   3 , Debbie A Walsh  1   2 , Jessica Mitchell  1   2 , Tim Clutton-Brock  1   4   5 , Christine M Drea  1   2   3   6
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Exceptional endocrine profiles characterise the meerkat: sex, status, and reproductive patterns

Charli S Davies et al. Sci Rep. .

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.

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Figures

Figure 1
Figure 1. In sexually mature meerkats, dominant females (red) and animals during reproductive events (hatched bars) generally have greater concentrations of sex steroids than do either subordinate females (pink), dominant males (dark blue), and subordinate males (light blue) or animals outside of reproductive events (solid bars), respectively.
Shown by sex and social status are mean + SEM baseline circulating concentrations of (top row) androstenedione (ng/ml), (middle row) testosterone (ng/ml) and (bottom row) estradiol (pg/ml). Shown by reproductive state for each steroid are (first column) baseline values (solid bars) for both sexes, (second column) subordinate male baseline values (solid bars) in relation to roving (hatched bars) and (third column) female baseline values (solid bars) in relation to pregnancy (hatched bars). Numbers of individuals are included for each category at the bottom of the bar graphs. ***P ψP < 0.10.
Figure 2
Figure 2. Concentrations of faecal androgen metabolites in sexually mature meerkats largely reproduce patterns observed for concentrations of serum androgens: dominant females (red) and animals during reproductive events (hatched bars) have greater concentrations than do either subordinate females (pink), dominant males (dark blue), and subordinate males (light blue) or animals outside of reproductive events (solid bars), respectively.
Shown are mean + SEM logged concentrations of faecal androgen metabolites (ng/g) by (a) baseline sex (solid bars) and social status for both sexes, (b) male baseline values (solid bars) in relation to roving (hatched bars) and (c) female baseline values (solid bars) in relation to pregnancy (hatched bars). Numbers of individuals are included for each category in the bottom of the bar graphs. ***P < 0.001, **P < 0.01 and *P < 0.05.
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