Sex steroid profiles align with phenotype in sex-reversed female lizards

Abstract

Vertebrate sex determination is remarkably diverse. In species with genetic sex determination, reproductive physiology and sex-specific behaviour are influenced by sex chromosomes and sex steroid hormones. However, some species experience sex reversal where the influence of sex chromosomes on sexual development is modulated by mutations or environmental conditions, leading to animals that phenotypically mismatch with their genotype. In these species, sex-reversed (‘discordant’) individuals can theoretically exhibit traits that are similar to either their phenotypic or genotypic sex. In the central bearded dragon (Pogona vitticeps), high incubation temperatures produce sex-reversed females with male-type sex chromosomes (ZZf). ZZf display a mix of male-like and intermediate traits compared to males (ZZm) and concordant females (ZWf). Sex steroid profiles could drive these differences but are yet to be examined in P. vitticeps. We measured testosterone (T) and estradiol (E2) in ZWf, ZZf, and ZZm dragons at three timepoints across a breeding season. As sex steroids can potentially affect offspring if maternal hormones are transmitted to eggs, we also compared T and E2 levels in egg yolks from ZZf and ZWf females. Sex-reversed ZZf had lower T levels than males and similar T and E2 levels to ZWf across the breeding season. ZWf and ZZf laid eggs with similar levels of T and E2. We found a negative association between maternal and yolk E2 levels, but no association between maternal and yolk T. Our results show that sex steroid profiles in sex-reversed ZZ female P. vitticeps reflect phenotypic, not genotypic sex, suggesting circulating sex steroids do not drive trait differences between discordant and concordant females.