Sex differences in brain structure and behaviour are well documented among vertebrates. An excellent model exploring the neural mechanisms of sex differences in behaviour is represented by sex-role-reversed species. In the majority of bird species, males compete over access to mates and resources more strongly than do females. It is thought that the responsible brain regions are therefore more developed in males than in females. Because these behaviours and brain regions are activated by androgens, males usually have increased testosterone levels during breeding. Therefore, in species with sex-role reversal, certain areas of the female brain should be more developed or steroid hormone profiles should be sexually reversed. Here, I studied circulating hormone levels and gene expression of steroid hormone receptors and aromatase in a captive population of barred buttonquails (Turnix suscitator). While females performed courtship and agonistic behaviours, there was no evidence for sexually reversed hormone profiles. However, I found female-biased sex differences in gene expression of androgen receptors in several hypothalamic and limbic brain regions that were already in place at hatching. Such sex differences are not known from non-sex-role-reversed species. These data suggest that increased neural sensitivity to androgens could be involved in the mechanisms mediating sex-role-reversed behaviours.
Supplementary Figure S1:
Autoradiograms of coronal sections through the brain of a female (Panels A-L) and male (Panels M-X) buttonquail at hatching day (P0) illustrating the expression of AR, ERα, ERβ and ARO mRNA visualised by in situ hybridisation. For each gene, sections are presented in a rostral to caudal order. Panels A-D and M-P are at the level of the anterior commissure.
Panels I-L and U-X are at the level of the caudal hypothalamus. Abbreviations: BSTM, bed
nucleus of the stria terminalis; CA, commisura anterior; ICo, nucleus intercollicularis; LS,
lateral septum; MBH, mediobasal hypothalamus; POM, medial preoptic nucleus; TnA,
nucleus taeniae of the amygdala.
Supplementary Video S1:
Sequence showing the performance of the booming call by a female barred buttonquail.
Supplementary Video S2:
Sequence showing the performance of a chase by a female barred buttonquail.
Supplementary Video S3:
Sequence showing the performance of courtship feeding by a female buttonquail.