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Abstract
Research into the development of reproductive technologies for amphibians has increased in recent years due to the rapid decline of amphibian species globally. Reproductive technologies have great potential to overcome captive breeding failure and improve the propagation and genetic management of threatened species. However, the incorporation of these technologies into conservation breeding programs has been protracted, primarily as a result of trial-and-error approaches to the refinement of hormone therapies. The present study investigated the effects of: (1) GnRH-a dose (0, 0.5, 1, 2, 4, 8 or 16 μg g-1), and (2) hCG dose (0, 2.5, 5, 10, 20 or 40 IU g-1), on the sperm-release response of the critically endangered Booroolong frog. Administration of GnRH-a at a dose of 0.5 μg g-1 resulted in the greatest number of sperm released (mean total sperm = 3.5 ×106, n = 11). Overall, hCG was more effective at eliciting spermiation in Booroolong frogs, with peak sperm release (mean total sperm = 25.1 ×106, n = 10) occurring in response to a dose of 40 IU g-1. Sperm output in response to 40 IU g-1 hCG was greatest between 1 and 6 h and steadily declined between 8 and 24 h post-hormone administration. Percent sperm motility peaked between 4 and 10 h (58.1-62.7%), and sperm velocity between 4 and 12 h (24.3-27.2 μm s-1). Booroolong frogs join a small, but growing number of amphibian species that exhibit improved spermiation in response to hCG. Further research is required to identify optimal hormone-induction protocols for threatened amphibians and expedite the incorporation of reproductive technologies into CBPs.
Highlights
Ongoing species decline and extinction continues to threaten vertebrate biodiversity across all taxonomic groups and geographic locations globally (Ceballos et al, 2015)
The number of frogs spermiating in response to 0 IU g−1 human chorionic gonadotropin (hCG) (0%) was significantly lower than the number of frogs spermiating in response to all other treatments (2.5, 5, 10, 20 or 40 IU g−1 hCG; 100 %; Fisher’s Exact tests, P < 0.05)
The total number of sperm released in response to the administration of 40 IU g−1 hCG differed significantly over time (LME; F13 = 12.131, P < 0.0001), with peak sperm release occurring between 1 and 6 h and steadily declining between 8 and 24 h post-hormone administration (Fig. 4a)
Summary
Ongoing species decline and extinction continues to threaten vertebrate biodiversity across all taxonomic groups and geographic locations globally (Ceballos et al, 2015). Amphibians have experienced an exceptionally rapid loss of biodiversity, with at least 2100 species at imminent risk of extinction, representing 31.8% of all described species (IUCN, 2017). In response to this extinction crisis, conservation breeding programs (CBPs) have been established for a number of threatened amphibian species with some evidence of successful reintroduction and species recovery (Harding et al, 2016). Reproductive failure threatens the genetic viability and adaptive capacity of captive colonies and in many cases has limited the generation of largenumbers of individuals for reintroduction (Silla and Byrne, 2019). When used in concert with traditional captive breeding methods, reproductive technologies may improve the efficiency and sustainability of CBPs and enhance program success (Silla and Byrne, 2019)
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