Development of assisted reproductive technologies for the conservation of Atelopus sp. (spumarius complex)

Abstract

Amphibians are in peril, given the ongoing sixth mass extinction of wildlife. Thus, Conservation Breeding Programs (CBPs) are attempting to breed some species under laboratory conditions. The incorporation of assisted reproduction technologies (ARTs), such as hormonal stimulation, sperm collection and cryopreservation, and in vitro fertilization is contributing to successful CBPs. The objective of this study was to apply ARTs in sexually mature individuals of an undescribed species of Atelopus (spumarius complex) (harlequin frog). Our procedure involves hormonal induction of gametogenesis in this species. We were able to induce gamete release through administration of human chorionic gonadotropin (hCG) in males, and in females this has been achieved through the sequential administration of hCG (priming doses), and combinations of hCG with gonadotropin releasing hormone analogue, GnRHa (ovulary dose). We standardized sperm cryopreservation by performing toxicity tests of cryoprotectants, fast/slow freezing and thawing, as well as supplementation of non-penetrating cryoprotectants (sugars). Next, we performed in vitro fertilization, evaluated the fertilization capacity of the cryopreserved sperm, and describe external features of fresh and cryopreserved sperm. We found that 10 IU/g hCG induced the release of the highest sperm concentrations between 3 and 5 h post-injection, while 2.5 IU/g hCG induced the release of eggs in most treated females. Under cryopreservation conditions, the highest recovery of forward progressive motility or FPM was 26.3 ± 3.5%, which was obtained in cryosuspensions prepared with the 5% DMF and 2.5% sucrose. Cryopreserved sperm showed narrower mitochondrial vesicles after thawing, while in frozen samples without cryodiluent showed 31% of spermatozoa lost their tails. In most cases, our attempts of in vitro fertilization were successful. However, only ∼10% of embryos were viable. Overall, our study demonstrates that the development of ARTs in individuals of Atelopus sp. (spumarius complex) bred in laboratory can be successful, which result in viable offspring through in vitro fertilization. Our study provides a baseline for assisted breeding protocols applicable to other harlequin frogs of the genus Atelopus.