Hormonal induction and seasonal variation in male reproductive viability of the Southern Rocky Mountain boreal toad.

Abstract

The Southern Rocky Mountain boreal toad (Anaxyrus boreas boreas) depends on both the rearing of wild-collected egg masses and a long-standing conservation breeding program (CBP), the latter of which heavily relies on assisted reproductive technologies (ARTs) to support wild populations. Achieving consistent reproductive success in the CBP, however, remains a significant challenge. Natural breeding has not led to a sustained increase in reproductive capacity, prompting the exploration of exogenous hormone treatments as an alternative strategy. This study specifically examined male responses to the administration of human chorionic gonadotropin (hCG), a previously tested hormone, in combination with gonadotropin-releasing hormone agonist (GnRH-A), either individually or together, to evaluate their effects on sperm induction and viability across different seasons. Insights into how hormone treatments and seasonality influence sperm acquisition can guide managers in improving breeding outcomes within ex situ populations by enhancing their understanding of reproductive health, applying hormone treatments at the optimal time of year, and determining the best timing for high quality sperm collection. These advancements can increase reproductive capacity and support long-term genetic management through biobanking. Results indicated that combining hCG and GnRH-A yielded the highest sperm quantity and quality, although further optimization of hormone dosages could improve outcomes. Seasonal factors significantly influenced hormonal efficacy, with variations in sperm concentration and quality observed across months.