Changes in Plasma Progesterone, Estrogen, and Testosterone Concentrations throughout the Reproductive Cycle in Female Viviparous Blue-Tongued Skinks, Tiliqua nigrolutea (Scincidae), in Tasmania

Abstract

Changes in mean plasma concentrations of progesterone (P4), estrogen (E) and testosterone (T) in a captive population of female viviparous skinks, Tiliqua nigrolutea were examined. Reproductively active and quiescent individuals were present in the population concurrently, allowing a comparison between these two conditions. Mean plasma progesterone concentrations were basal (1-2 ng ml-1) until the start of gestation and peaked in the second trimester (12.7 +/- 1.27 ng ml-1), before falling significantly prior to parturition. An increase in mean plasma estrogen concentrations occurred coincident with the vitellogenic period; mean plasma estrogen concentration peaked at 715.1 +/- 106.68 pg ml-1 shortly before ovulation. Mean plasma testosterone concentrations in reproductively active females peaked in the periovulatory period (6.3 +/- 0.63 ng ml-1) and had returned to basal concentrations (< 1 ng ml-1) two weeks later. Changes in mean plasma steroid concentrations were correlated with reproductive condition, and are discussed in terms of potential in vivo steroid interactions and the multihormone control of reproduction.