For other species, replicating the specific environmental stimuli required for reproduction has been unsuccessful, and these programs have been hindered by an inability to reliably and predictably initiate amphibian breeding behaviour, achieve high rates of fertilization or generate large numbers of genetically diverse and viable offspring ( Kouba et al., 2009 Silla and Byrne, 2019). A number of programs report partial to high success rates following the provision of traditional methods of environmental manipulation to induce reproduction in captivity. Captive breeding and reintroduction programs (also known as conservation breeding programs) have been established for several threatened and endangered amphibian species globally, assisting to prevent species extinction by maintaining genetically representative captive assurance colonies, while providing individuals for release ( Silla and Byrne, 2019). In response to the amphibian biodiversity crisis, several important interventionist conservation actions have been recommended, including the establishment of ex situ captive breeding and reintroduction programs ( Gascon et al., 2007). A moral and ethical obligation now exists to assist threatened species recovery and protect species from further decline ( Minteer and Collins, 2013). All vertebrate classes have been affected, though amphibians are exhibiting the most dramatic declines, with an estimated 41% of species threatened with extinction ( IUCN, 2020). Unprecedented rates of species decline have resulted in the sixth mass extinction currently threatening global biodiversity and ecosystem functioning. Further research is required to develop hormone therapies for a greater number of species to boost global conservation efforts.

We summarize advances in hormone therapies and discuss two case studies that illustrate some of the challenges and successes with amphibian reproductive technologies: the mountain yellow-legged frog ( Rana muscosa USA) and the northern corroboree frog ( Pseudophryne pengilleyi Australia). Species-dependent methods for handling, restraint and hormone administration (including route and frequency) are discussed to ensure optimal welfare of captive breeding stock. Reproductive technologies have the potential to overcome these challenges but should be used in concert with traditional methods that manipulate environmental conditions (including temperature, nutrition and social environment).

As a result, many amphibian captive breeding programs fail to reliably initiate breeding behaviour, achieve high rates of fertilization or generate large numbers of healthy, genetically diverse offspring. While the amphibian hypothalamo–pituitary–gonadal (HPG) axis shares fundamental similarities with both teleosts and tetrapods, there are more species differences than previously assumed. This reflects our relatively poor understanding of the hormonal control of amphibian reproduction and the stimuli required to initiate and complete reproductive events. Captive breeding and reintroduction programs have been established for several threatened amphibian species globally, but with varied success.

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