Characterization of fecal hormone patterns associated with the reproductive cycle in female veiled chameleons ( Chamaeleo calyptratus)

Abstract

Reptiles have gained popularity in the North American and European pet trade. Large numbers of captive-born veiled chameleons, Chamaeleo calyptratus, are produced annually but knowledge of their reproductive cycle has been limited to anecdotal observations. This study describes the hormonal changes associated with reproductive cycling in female veiled chameleons using non-invasive fecal evaluation of metabolites of the three principal ovarian steroids, estradiol (E2), testosterone (T), progesterone (P), and their metabolites, by enzyme immunoassays. The hormone patterns were compared with follicular development and ovulation as determined by magnetic resonance imaging (MRI). Three main cycle stages were identified on MRI: the previtellogenic stage (PV) with the absence of visible follicular structures, vitellogenic stage (V) with the presence of round follicular structures >2 mm diameter, and the gravid stage with the presence of oval egg structures. Although the absolute values of the baselines and peaks for each hormone varied among animals, approximately 24-fold increases over mean P baseline values and 7.5-fold increases over mean E2 and T baseline values were associated with biological events. E2 rose during vitellogenesis, peaked in late vitellogenesis and fell shortly thereafter. P rose during the late vitellogenic stage, peaked in mid-gravidity and fell to baseline values at oviposition. Ovulation occurred with the decreasing E2:P ratio. T levels varied during the pre- and vitellogenic stages then mirrored P with a distinct peak during the time of ovulation and gravidity. These data provides us with the necessary background for future studies on the reproductive biology of this species.