Seasonal patterns of plasma steroid hormones in males and females of the bearded dragon lizard, Pogona barbata.

Pogona barbata is an Australian lizard that produces several large clutches of eggs between August and December (spring to early summer). Mating takes place around ovulation. The seasonal pattern of reproductive hormones in males and females of P. barbata was determined by radioimmunoassay of plasma progesterone (P), estradiol-17beta (E-17beta), corticosterone (B), and total androgen (TA). In females, P began to rise in August and was elevated from September to December. Corticosterone and TA were detectable but low and did not vary with time of year or reproductive condition. Estradiol-17beta was only detectable in a few females and exhibited no elevation with vitellogenic activity. These results suggest that B and TA are not involved in female reproduction. Estrogens may be either so low they could not be detected or they were present in a form other than estradiol-17beta. The high sensitivity of the estradiol-17beta radioimmunoassay suggests the latter. In males, TA peaked at the beginning of spring. They then declined to a minimum during November and December. However, concentrations recovered in the postbreeding activity period, January to April (summer and autumn). These patterns are consistent with the observation of maximum spermatogenic activity in spring, followed by the cessation of spermatogenesis directly after the breeding period and testicular recrudescence in February (late summer).