Annual cycles of reproductive steroids in the Blotched Blue-tongued Lizard, Tiliqua nigrolutea (Scincidae)

T. nigrolutea is a large skink distributed across south-eastern mainland Australia and Tasmania. This species is torpid throughout winter with males emerging (Sept-Oct), roughly one month before females (Nov) in spring. Mating occurs in November, with gestation for approximately three months over summer. Parturition occurs in early autumn.\ \ I have investigated the annual cycles of the sex steroids, progesterone (P4) and testosterone (T), in T. nigrolutea. Captive animals were maintained under natural lighting conditions with supplementary heat for basking. In females, plasma P4 levels increase through early pregnancy. Concentrations peak (6.3 plus or minus 2.2 ng/ml) during the second trimester (Feb) and drop to basal levels (< 1 ng/ml) before parturition. This closely resembles the pattern previously reported for the sleepy lizard, T. rugosa, and is comparable with hormone profiles during pregnancy in some other viviparous reptiles. Plasma T in males peaks (10.2 plus or minus 3.5 ng/ml) in October, coincident with peak testis size, the presence of mature sperm in the testis and aggressive male-male interactions. This peak in plasma T concentration is, however, temporally dissociated from mating behaviour and plasma T concentrations are lower than those reported for other reptiles.