Repeated exogenous hormone administration decreases sperm quantity and quality in threatened frog species (Litoria aurea)

Assisted reproductive technologies are important for protecting threatened amphibian species globally. These technologies can overcome amphibian breeding failure and improve threatened species management and research quality in the fields of reproductive biology and ecology. One assisted reproductive technology is inducing spermiation using exogenous hormone injections. However, the impacts of repeatedly administering exogenous hormones on sperm quality and quantity remain poorly understood. In this study we repeatedly administered an exogenous hormone - human chorionic gonadotropin - in the threatened Australian frog species, Litoria aurea. We analysed sperm quantity and quality over 3-4 hormonal administrations at biweekly, weekly, and fortnightly frequencies (n = 6 for each group). Sperm quality and quantity were assessed at three timepoints over a 6-hour period following each hormonal administration (hours 2, 4, and 6 post-injection). We found that repeated administrations significantly reduced sperm quantity and quality via reduced concentration, volume, total sperm counts, and viability. With repeated administrations, the timing of sperm release varied: after only one administration, sperm was released equivalently in hours 2, 4 and 6 post-injection, whereas after several administrations, sperm release was delayed such that 6 hr post-injection produced higher quantity and quality sperm. Overall, our results demonstrate that repeated hormonal administration of male L. aurea reduces sperm quantity and quality, and individuals will need substantial time to regenerate sperm between administrations.