Aromatase, 5 alpha- and 5 beta-reductase in brain, pituitary and skin of the sex-role reversed Wilson's phalarope.

Abstract

While intrasexual competition for mates is generally considered to be an androgen-dependent characteristic of reproductively active males, in the Wilson's phalarope (Phalaropus tricolor) it is the female that acquires the brighter nuptial plumage and aggressively competes for access to the less aggressive males. Despite this pronounced sex-role reversal, circulating sex steroid hormones of breeding phalaropes are similar to those of avian species displaying traditional male-female reproductive roles. To investigate whether these behavioural and morphological steroid-dependent differences may be due to differences in target organ metabolism of circulating androgen, [3H]androstenedione in the presence of an NADPH-generating system was incubated with homogenates of brain, pituitary and skin of male and female Wilson's phalaropes collected from a naturally breeding population. Oestrone, 5 alpha-androstanedione and 5 beta-androstanedione were measured as endpoints of aromatization, 5 alpha-reduction and 5 beta-reduction respectively. Aromatase activity in the anterior hypothalamus/preoptic area (AHPOA) and posterior hypothalamus was greater in breeding males with high circulating concentrations of testosterone than in females, and activity in the AHPOA was greater in breeding than in non-breeding males (with low circulating testosterone). Aromatase levels did not differ in septum, archistriatum, hyperstriatum or pituitary. 5 alpha- and 5 beta-reductase were detected in all neuroendocrine tissues sampled and although there were no significant male-female differences, 5 alpha-reductase was greater in the AHPOA of breeding than of nonbreeding males.(ABSTRACT TRUNCATED AT 250 WORDS)