Amphibian Declines in the Twenty-First Century: Why We Need Assisted Reproductive Technologies

Abstract

Each amphibian species is evolutionarily distinct, having developed highly specialized and diverse reproductive strategies in both terrestrial and aquatic environments. These unique reproductive patterns and mechanisms, key to species propagation, have only been explored in a limited number of laboratory models. Although the development of applied reproductive technologies for amphibians has proven useful for a few threatened species, the real benefit of this technology has been new insights into the reproductive adaptations, behavior, endocrinology, and physiological mechanisms that have evolved over millions of years. As the basic fundamental database on amphibian reproductive physiology has grown, so has the applied benefit for species conservation. In particular, technologies such as non-invasive fecal and urinary hormone assays, hormone treatments for induced breeding or gamete collection, in vitro fertilization, and the ability to establish genome resource banks have all played important roles in monitoring or managing small populations of captive species. Amphibians have the ability to produce a large excess of germplasm (up to 10,000 ovulated eggs in a single reproductive event) that if not collected and preserved, would represent a wasted valuable resource. We discuss the current state of knowledge in assisted reproductive technologies for amphibians and why their extinction crisis means these available tools can no longer be implemented as small-scale, last-ditch efforts. The reproductive technologies must be established early as a key component of large-scale species recovery.

Reproductive Techniques for Ovarian Monitoring and Control in Amphibians

“…Other than seasonality and the associated circulating hormone milieu, ovarian control may also be tightly linked to age, time spent in captivity and exposure to repeated hormone administration, for which there is little information in the literature 11,12,13 . The implementation of hormone therapies to elicit reproductive behaviors, gamete production, maturation and oviposition has become a widely reported approach to resolving common reproductive problems associated with captivity 4,8,14,15,16 . Because the mechanisms controlling reproduction in vertebrates are highly conserved, there are a number of hormones, neuropeptides and commercially available drugs used therapeutically in other taxonomic groups that can also be used reliably in a number of amphibian species ( Table 1).…”

“…In in vitro studies, PGF 2α is a potent inducer of ovulation 31 , while in vivo it can induce oviposition of retained eggs in Rana muscosa 4,30,32 . Pituitary extracts are also effective inducers of ovulation 15,16,34 ; however, concerns surrounding biosecurity and the potential for disease transmission are often a deterrent for captive breeding colonies when considering this approach 35 .…”

Effects of freezing and activation on membrane quality and DNA damage in Xenopus tropicalis and Xenopus laevis spermatozoa

“…In the face of the current global amphibian extinction crisis, sperm cryopreservation represents a key potential strategy for supporting threatened populations and enabling the future reestablishment of recently extinct species (Clulow et al 2014). There is also increasing interest in the use of sperm cryopreservation for storing genetically altered lines of amphibians, especially Xenopus laevis and Xenopus tropicalis, given their growing importance as biomedical models (Khokha 2012;O'Neill and Ricardo 2013;Pratt and Khakhalin 2013;Schmitt et al 2014).…”

Effects of hormonal stimulation on the concentration and quality of excreted spermatozoa in the critically endangered Panamanian golden frog (Atelopus zeteki)

“…Males amphibians excrete spermic urine following hormonal stimulations but results vary among species [9,13,14]. Human chorionic gonadotropin (hCG) has been widely used in numerous amphibian species including Xenopus, Bufo and Litoria to collect spermic urine [15][16][17][18].…”