Fecal testosterone concentrations may not be useful for monitoring reproductive status in male blue-tongued lizards (Tiliqua nigrolutea: Scincidae)

Abstract

Assessment of reproductive status in animals generally depends on monitoring hormone concentrations in plasma, but blood sampling often involves significant stress to the subject. Monitoring steroid profiles by assaying excreted steroids in urine and/or fecal samples is non-invasive, but does pose some problems.There are, however, only two published reports of the application of fecal steroid monitoring to reptiles. We compare the profile of fecal T with that for plasma T through the reproductive cycle of blotched blue-tongued lizards, and also examine the relative proportions of conjugated and free T in feces. Testosterone was detected in all samples assayed, and fecal T concentrations ranged from ~ 500 ng g-1 to ~1500 ng g-1 dry feces. Plasma hormone cycles were not reported, but the patterns of variation in fecal T concentrations appeared to show some correlation with reproductive activity. In contrast, our results suggest that there is an inverse relationship between concentrations of T in feces and in plasma of male blue-tongued skinks, with fecal T concentrations being highest during the non-breeding season, when plasma T levels are low. Our results suggest, therefore, that assay of fecal T concentrations may not be useful for assessing reproductive status in blue-tongued lizards because of the lack of correlation between T concentrations in feces and plasma.