Predicting the gender of subadult Komodo dragons (Varanus komodoensis) using two-dimensional ultrasound imaging and plasma testosterone concentration

Abstract

Six yearling Komodo dragons (Varanus komodoensis) underwent ultrasound examinations every three months over a nine-month period to assess the value of two-dimensional ultrasound imaging technology for the purpose of determining gender in this highly monomorphic species. Beginning at an age of 28 months, ovarian structures could be imaged, allowing a prediction of gender based on the presence or absence of ovarian follicles. Simultaneously, plasma testosterone concentration was measured monthly on each individual during the study period. Beginning at an age of 24 months, putative males had consistently elevated plasma testosterone values that were ∼40–60 times greater than those of putative females. In a blind comparison, predictions of gender based on plasma testosterone values matched the prediction of sex based on ultrasound imaging for all six individuals. The results indicate that measurements of circulating testosterone and two-dimensional ultrasound imaging together appear useful in the noninvasive determination of gender in juvenile V. komodoensis at just over two years of age. © 1996 Wiley-Liss, Inc.