Changes in Plasma Testosterone, Estrogen, and Progesterone Concentrations Throughout the Annual Reproductive Cycle in Male Viviparous Blue-Tongued Skinks, Tiliqua nigrolutea, in Tasmania

Abstract

Few published studies have detailed comprehensively the correlations between plasma ste- roid hormone peaks and the timing of reproductive events in male squamate reptiles. We examined the patterns of plasma testosterone (T), estrogen (E) and progesterone (P4) concentrations in males of the vivip- arous blue-tongued skink, Tiliqua nigrolutea, throughout the annual cycle. Plasma T concentrations varied throughout the annual cycle, peaking at 10.9 ? 3.00 ng ml-' during spermiogenesis, coincident with agonistic male-male interactions, but falling prior to the mating period. Mean plasma T concentrations were basal (2-3 ng ml-1) during reproductive quiescence. Mean plasma E concentrations were significantly elevated (778.0 ? 120.00 pg ml-') during the mating period but basal (< 300 pg ml-1) both before and after mating. Mean plasma P4 concentrations peaked during the mating period (1.1 ? 0.17 ng ml-') and declined signif- icantly after mating. We propose a potential role for E and P4 in the stimulation of male reproductive behavior during the mating period.