Differential success in obtaining gametes between male and female Australian temperate frogs by hormonal induction: A review

Refrigerated storage and cryopreservation of hormonally induced sperm in the threatened frog, Litoria aurea

As sperm cryopreservation and other assisted reproductive technologies (ARTs) advance in common amphibian species, focus on applying non-lethal sperm collection methods to the conservation and genetic management of threatened species is imperative. The goal of this study was to examine the application of logistically practical ART protocols in a threatened frog (Litoria aurea). First, we tested the efficacy of various concentrations of human chorionic gonadotropin (hCG) (20, 40 IU/g bodyweight) and Gonadotropin releasing hormone antagonist (0.25 µg/g and 0.5 µg/g body weight GnRH-a) on the induction of spermatozoa. Using the samples obtained from the previous trials, we tested the effect of cold storage and cryopreservation protocols on long-term refrigerated storage and post-thaw sperm recovery. Our major findings include: (1) high quality sperm were induced with 20 and 40 IU/g bodyweight of (hCG); (2) proportions of live, motile sperm post-thaw, were recovered at higher levels than previously reported for L. aurea (>50%) when preserved with 15% v/v DMSO and 1% w/v sucrose; and (3) spermic urine stored at 5 °C retained motility for up to 14 days. Our findings demonstrate that the protocols developed in this study allowed for successful induction and recovery of high-quality spermatozoa from a threatened Australian anuran, L. aurea, providing a prime example of how ARTs can contribute to the conservation of rare and threatened species.

Cryopreservation Cooling Rate Impacts Post-Thaw Sperm Motility and Survival in Litoria booroolongensis

The cryopreservation and storage of gametes (biobanking) can provide a long-term, low-cost option for the preservation of population genetic diversity and is particularly impactful when applied to manage selective breeding within conservation breeding programs (CBPs). This study aimed to develop a sperm cryopreservation protocol for the critically endangered Booroolong frog (Litoria booroolongensis) to capture founder genetics within the recently established (est. 2019) CBP for this species. Hormone-induced sperm release was achieved using established protocols, and spermic urine samples were collected over a 6-h period. Pooled spermic urine samples (n = 3 males) were divided equally between two cryoprotectant (CPA) treatments and diluted by 1:5 (sperm:CPA) with either 15% (v/v) dimethyl sulfoxide + 1% (w/v) sucrose in simplified amphibian Ringer's (SAR; CPAA) or 10% (v/v) dimethylformamide + 10% (w/v) trehalose dihydrate in SAR (CPAB). The samples were cryopreserved in 0.25 mL straws using either a programmable freezer (FrA) or an adapted dry shipper method (FrB). The thawed samples were activated via dilution in water and assessed for viability and motility using both manual assessment and computer-assisted sperm analysis (CASA; 0 h, 0.5 h post-thaw). Upon activation, the survival and recovery of motility (total motility, forward progression and velocity) of cryopreserved sperm suspensions were higher for sperm preserved using FrB than FrA, regardless of CPA composition. This work supports our long-term goal to pioneer the integration of biobanked cryopreserved sperm with population genetic management to maximize restoration program outcomes for Australian amphibian species.

Recovery and Characterization of Spermatozoa in a Neotropical, Terrestrial, Direct-Developing Riparian Frog (Craugastor evanesco) through Hormonal Stimulation

The Vanishing Rainfrog (Craugastor evanesco) is an endemic and critically endangered frog species of Panama. It is suspected that 90% of the population has disappeared from the wild. Frogs were collected from the wild and brought to a Captive Breeding Program; however, accomplishing regular reproductive events for this species has been difficult. The objective of this study was to determine the effect of hormonal stimulation on the production and quality of C. evanesco spermatozoa, aiming to develop an efficient and safe sperm collection protocol as a tool to help reproduce this endangered species. Mature males received intra-peritoneal injections with one of six hormone treatments, including des-Gly10, D-Ala6, Pro-NHEt9-GnRH-A, Amphiplex or hCG. Urine samples were collected at 10 different time points post-injection. Quality assessments included sperm concentration, percentage motility, percentage forward progressive motility (FPM), osmolality, pH and morphology analysis. Our results indicate that the optimal treatment for the collection of highly concentrated sperm samples of C. evanesco is 4 µg/gbw GnRH, followed by Amphiplex and 2 µg/gbw GnRH as sub-optimal treatments and finally, 6 µg/gbw GnRH and 5 and 10 IU/gbw hCG as non-optimal treatments. GnRH-A at 4 μg/gbw and Amphiplex stimulated the production of samples with the highest sperm concentrations and quality, despite Amphiplex producing lower percentages of intact acrosome and tail. In contrast, hCG concentrations were not reliable inducers of sperm production, consistently showing lower concentrations, higher percentages of sperm abnormalities and more acidic spermic urine than that induced by Amphiplex and GnRH-A. Morphological assessments revealed that C. evanesco spermatozoa have a filiform shape with a large acrosome on the anterior part of an elongated head, a small midpiece and a long tail with two filaments joined together by an undulating membrane.

Application of Reproductive Technologies to the Critically Endangered Baw Baw Frog, Philoria frosti

Reproductive technologies (RTs) can assist integrated conservation breeding programs to attain propagation targets and manage genetic diversity more effectively. While the application of RTs to enhance the conservation management of threatened amphibians has lagged behind that of other taxonomic groups, a recent surge in research is narrowing the divide. The present study reports on the first application of RTs (hormone-induced spawning, hormone-induced sperm-release, and sperm cryopreservation) to the critically endangered Baw Baw frog, Philoria frosti. To determine the effect of hormone therapy on spawning success, male-female pairs were administered either 0 μg/g gonadotropin-releasing hormone agonist (GnRHa), 0.5 μg/g GnRHa, or 0.5 μg/g GnRHa + 10 μg/g metoclopramide (MET) (n = 6-7 pairs/treatment), and the number of pairs ovipositing, total eggs, and percent fertilisation success were quantified. To determine the effect of hormone therapy on sperm-release and to establish the peak time to collect sperm post-hormone administration, males were administered 0 IU/g (n = 4), or 20 IU/g hCG (n = 16). Total sperm, sperm concentration, and percent viability were quantified at 0, 2, 4, 6, 8, 10, and 12 h post-hormone administration. Overall, the percentage of pairs ovipositing was highest in the GnRHa + MET treatment, with 71% of pairs ovipositing, compared to 57% and 33% of pairs in the GnRHa and control treatments, respectively. The quantity of sperm released from males in response to hCG peaked at 4 h post-hormone administration, though it remained high up to 12 h. The percent sperm viability also peaked at 4 h post-administration (94.5%), exhibiting a steady decline thereafter, though viability remained above 77% throughout the 12 h collection period. The remaining sperm samples (n = 22) were cryopreserved using established protocols and biobanked for long-term storage and future conservation applications. The mean post-thaw sperm viability was 59%, and the percent total motility was 17%. The results from this preliminary study will direct further applications of RTs to the critically endangered Baw Baw frog to assist with species recovery.

The Increasing Role of Short-Term Sperm Storage and Cryopreservation in Conserving Threatened Amphibian Species

Multidisciplinary approaches to conserve threatened species are required to curb biodiversity loss. Globally, amphibians are facing the most severe declines of any vertebrate class. In response, conservation breeding programs have been established in a growing number of amphibian species as a safeguard against further extinction. One of the main challenges to the long-term success of conservation breeding programs is the maintenance of genetic diversity, which, if lost, poses threats to the viability and adaptive potential of at-risk populations. Integrating reproductive technologies into conservation breeding programs can greatly assist genetic management and facilitate genetic exchange between captive and wild populations, as well as reinvigorate genetic diversity from expired genotypes. The generation of offspring produced via assisted fertilisation using frozen-thawed sperm has been achieved in a small but growing number of amphibian species and is poised to be a valuable tool for the genetic management of many more threatened species globally. This review discusses the role of sperm storage in amphibian conservation, presents the state of current technologies for the short-term cold storage and cryopreservation of amphibian sperm, and discusses the generation of cryo-derived offspring.

Captive breeding in the endangered alpine tree frog, Litoria verreauxii alpina

Amphibians are experiencing dramatic worldwide declines and many species are reliant on captive breeding programs to ensure continued survival. However, captive breeding in amphibians is not always successful because many species, especially ones in decline, have particular and specific breeding needs. The endangered alpine tree frog, Litoria verreauxii alpina, has never been bred in captivity before. Due to its dramatic declines across the Australian Alps caused by the global pandemic chytridiomycosis, the species is a potential candidate for captive assurance colonies, which rely on captive breeding. For this study we tested hormone induction using two hormones that have had some success in other amphibian species, to no avail. We then tried outdoor breeding mesocosms during the winter/spring at temperatures similar to their natural breeding season, which was successful. Sixty-five percent of the egg masses laid successfully hatched tadpoles. Females laid more than one clutch over the experiment indicating either a shorter than annual ovulation cycle, or that females are capable of partial ovulation during breeding events. Outdoor breeding mesocosms are a possibility outside the native climate of a species, provided that temperatures overlap with their natural environment. Here, we highlight that troubleshooting is essential before embarking on a captive breeding program of a species that has not been bred before. Hormonal induction of breeding is not always successful; therefore, outdoor mesocosms might be required to achieve healthy tadpoles.

Sperm parameters following hormonal induction of spermiation in an endangered frog [the alpine tree frog] (Litoria verreauxii alpina)

CONTEXT

With global amphibian biodiversity rapidly declining, improving reproductive technology outcomes has become essential. Captive breeding programs have struggled because amphibian breeding physiology often requires specific environmental cues that reproductive technologies can circumvent.

AIMS

This study tests the efficiency of hormonal induction by evaluating sperm quality in the endangered Litoria verreauxii alpina.

METHODS

We assessed the effects of exogenous hormones - gonadotrophin-releasing hormone agonist (GnRH-a, Lucrin), and human chorionic gonadotrophin (hCG, Chorulon) - on sperm quality.

KEY RESULTS

Hormone induction with hCG showed high efficacy while GnRH-a yielded a low response in producing sperm. Sperm quantity was affected by time post injection, with the greatest quantity at 1h post injection. Sperm quality was also affected by time, where the sperm head size decreased by 11% at 7h post injection.

CONCLUSIONS

Based on the results from this study, we recommend that that sperm be collected soon after induction, and not more than 4h post induction in L. v. alpina. More work needs to be completed before recommending an optimal hormone induction method and dose, but 120IU of hCG per male was successful for inducing spermiation.

IMPLICATIONS

This study represents a useful starting point for developing assisted reproductive techniques for non-model organisms.

Common goals, different stages: the state of the ARTs for reptile and amphibian conservation

Amphibians and reptiles are highly threatened vertebrate taxa with large numbers of species threatened with extinction. With so many species at risk, conservation requires the efficient and cost-effective application of all the tools available so that as many species as possible are assisted. Biobanking of genetic material in genetic resource banks (GRBs) in combination with assisted reproductive technologies (ARTs) to retrieve live animals from stored materials are two powerful, complementary tools in the conservation toolbox for arresting and reversing biodiversity decline for both amphibians and reptiles. However, the degree of development of the ARTs and cryopreservation technologies differ markedly between these two groups. These differences are explained in part by different perceptions of the taxa, but also to differing reproductive anatomy and biology between the amphibians and reptiles. Artificial fertilisation with cryopreserved sperm is becoming a more widely developed and utilised technology for amphibians. However, in contrast, artificial insemination with production of live progeny has been reported in few reptiles, and while sperm have been successfully cryopreserved, there are still no reports of the production of live offspring generated from cryopreserved sperm. In both amphibians and reptiles, a focus on sperm cryopreservation and artificial fertilisation or artificial insemination has been at the expense of the development and application of more advanced technologies such as cryopreservation of the female germline and embryonic genome, or the use of sophisticated stem cell/primordial germ cell cryopreservation and transplantation approaches. This review accompanies the publication of ten papers on amphibians and twelve papers on reptiles reporting advances in ARTs and biobanking for the herpetological taxa.

Reproduction technologies for the sustainable management of Caudata (salamander) and Gymnophiona (caecilian) biodiversity

We review the use of reproduction technologies (RTs) to support the sustainable management of threatened Caudata (salamanders) and Gymnophiona (caecilian) biodiversity in conservation breeding programs (CBPs) or through biobanking alone. The Caudata include ∼760 species with ∼55% threatened, the Gymnophiona include ∼215 species with an undetermined but substantial number threatened, with 80% of Caudata and 65% of Gymnophiona habitat unprotected. Reproduction technologies include: (1) the exogenous hormonal induction of spermatozoa, eggs, or mating, (2) in vitro fertilisation, (3) intracytoplasmic sperm injection (ICSI), (4) the refrigerated storage of spermatozoa, (5) the cryopreservation of sperm, cell or tissues, (6) cloning, and (7) gonadal tissue or cell transplantation into living amphibians to eventually produce gametes and then individuals. Exogenous hormone regimens have been applied to 11 Caudata species to stimulate mating and to 14 species to enable the collection of spermatozoa or eggs. In vitro fertilisation has been successful in eight species, spermatozoa have been cryopreserved in seven species, and in two species in vitro fertilisation with cryopreserved spermatozoa has resulted in mature reproductive adults. However, the application of RTs to Caudata needs research and development over a broader range of species. Reproduction technologies are only now being developed for Gymnophiona, with many discoveries and pioneering achievement to be made. Species with the potential for repopulation are the focus of the few currently available amphibian CBPs. As Caudata and Gymnophiona eggs or larvae cannot be cryopreserved, and the capacity of CBPs is limited, the perpetuation of the biodiversity of an increasing number of species depends on the development of RTs to recover female individuals from cryopreserved and biobanked cells or tissues.

Near-Infrared Spectroscopy (NIRS) as a Method for Biological Sex Discrimination in the Endangered Houston Toad (Anaxyrus houstonensis)

Biological sex is one of the more critically important physiological parameters needed for managing threatened animal species because it is crucial for informing several of the management decisions surrounding conservation breeding programs. Near-infrared spectroscopy (NIRS) is a non-invasive technology that has been recently applied in the field of wildlife science to evaluate various aspects of animal physiology and may have potential as an in vivo technique for determining biological sex in live amphibian species. This study investigated whether NIRS could be used as a rapid and non-invasive method for discriminating biological sex in the endangered Houston toad (Anaxyrus houstonensis). NIR spectra (N = 396) were collected from live A. houstonensis individuals (N = 132), and distinct spectral patterns between males and females were identified using chemometrics. Linear discriminant analysis (PCA-LDA) classified the spectra from each biological sex with accuracy ≥ 98% in the calibration and internal validation datasets and 94% in the external validation process. Through the use of NIRS, we have determined that unique spectral signatures can be holistically captured in the skin of male and female anurans, bringing to light the possibility of further application of this technique for juveniles and sexually monomorphic species, whose sex designation is important for breeding-related decisions.

Impacts of invasive cane toads on an Endangered marsupial predator and its prey

Recent research has revealed that impacts of some invasive species are chronic. Invasive cane toads Rhinella marina have apparently caused rapid and severe population-level declines of the Endangered northern quoll Dasyurus hallucatus across tropical Australia; however, more targeted, quantitative impact data are needed to disentangle this from other threats such as fire regimes, disease, feral cats and dingos. Moreover, repeatable counts before, during, after and long after toad invasion are needed in order to determine if short-term impacts are chronic vs. transitory. We used game cameras to monitor 2 quoll populations and their prey over a 5 yr period spanning the invasion of the toxic cane toads in 2 gorges in northwestern Australia. We predicted severe declines in quolls with the toad invasion, and predatory release of 2 prey species of quolls, a rodent and a smaller marsupial. Quolls declined quickly upon arrival of toads, becoming undetectable in one gorge and barely detectable in the other. Identification of individuals via unique spot patterns confirmed that the declines in detection rates were due to changes in relative abundance rather than decreases in activity. Despite quoll declines we found no evidence of mesopredator release; small mammals generally declined as toads arrived. Our research confirmed rapid population-level declines of quolls, and possibly smaller mammals, associated with arrival of invasive cane toads. Importantly, our surveys provide a baseline for future surveys to determine whether these short-term impacts are chronic or transitory, and whether recovery requires assistance from managers.

Influence of oviposition-inducing hormone on spawning and mortality in the endangered Panamanian golden frog (Atelopus zeteki)

Background

With Panamanian golden frogs (Atelopus zeteki; PGFs) likely extirpated from the wild, ensuring long-term sustainability of captive populations is crucial in order to conserve this critically endangered species. Unfortunately, PGFs display a unique reproductive behavior involving a prolonged period of amplexus leading to challenges in their successful captive propagation. The Maryland Zoo in Baltimore has observed high levels of mortality during the breeding season and suboptimal reproductive success leading to the use of hormone stimulation to aid in reproduction and health management.

Methods

This project aimed to develop induced ovulation and health management protocols by (1) evaluating different doses of gonadotropin releasing hormone analogue (GnRHa), (2) comparing the efficacy of GnRHa and GnRHa + metoclopramide, (3) determining latency periods and the effects of pulsed hormone sequences; and (4) establish if mortality is impacted by hormone therapy. Female PGFs (n = 174) were given GnRHa either in various concentrations (Experiment 1) or combined with metoclopramide (Experiment 2), and oviposition success, latency, and mortality were measured as binary response variables.

Results

Overall, the use of exogenous hormones significantly decreased mortality when compared to the control data of natural egg-laying females. GnRHa doses of 0.05 μg/g body weight produced similar ovulation rates compared to higher doses, and the addition of metoclopramide did not increase oviposition success compared to GnRHa alone. Lastly, results indicate the majority of female PGFs will release eggs within 48 h following the initial pulse of hormones with a small percentage ovipositing after a second pulse.

Conclusion

Findings from this study will benefit captive management of PGFs by documenting the increased survival of females when given hormone stimulation and defining appropriate GnRHa doses and expected latency to spawning.

Cryopreservation of spermatozoa obtained postmortem from the European common frog Rana temporaria

Cryopreserved spermatozoa offers a reliable, efficient and cost-effective means to perpetuate the genetic variation of endangered amphibian species in concert with conservation breeding programs. Here we describe successful cryopreservation of testicular spermatozoa of the common frog Rana temporaria , preliminarily stored in the carcasses of decapitated animals at +4°C for 0, 1 and 4 days. The motility, membrane integrity and fertilisation capability of fresh testicular spermatozoa treated with cryoprotective medium supplemented with 15% dimethylformamide (DMF) or 15% dimethylsulfoxide (DMSO) were examined. DMSO had a significantly greater toxic effect on fresh frog spermatozoa than DMF. Low levels of DNA fragmentation were seen in spermatozoa stored in the testis for different times and then treated with DMF (mean (±s.e.m.) 8.2±0.7% and 18.2±1.8% after 0 and 4 days storage respectively). After 1 day of storage in frog carcasses, the quality of spermatozoa cryopreserved with DMF was not significantly different from that of control spermatozoa (0 days of storage). After 4 days of storage, the quality of frozen-thawed spermatozoa was significantly lower in the DMF-treated than control group: 35% of the spermatozoa cryopreserved with DMF retained motility, 25% maintained the ability to fertilise fresh oocytes and 80% of fertilised oocytes survived to hatch.

Integrating biobanking could produce significant cost benefits and minimise inbreeding for Australian amphibian captive breeding programs

Captive breeding is an important tool for amphibian conservation despite high economic costs and deleterious genetic effects of sustained captivity and unavoidably small colony sizes. Integration of biobanking and assisted reproductive technologies (ARTs) could provide solutions to these challenges, but is rarely used due to lack of recognition of the potential benefits and clear policy direction. Here we present compelling genetic and economic arguments to integrate biobanking and ARTs into captive breeding programs using modelled captive populations of two Australian threatened frogs, namely the orange-bellied frog Geocrinia vitellina and the white bellied frog Geocrinia alba . Back-crossing with frozen founder spermatozoa using ARTs every generation minimises rates of inbreeding and provides considerable reductions in colony size and program costs compared with conventional captive management. Biobanking could allow captive institutions to meet or exceed longstanding genetic retention targets (90% of source population heterozygosity over 100 years). We provide a broad policy direction that could make biobanking technology a practical reality across Australia's ex situ management of amphibians in current and future holdings. Incorporating biobanking technology widely across this network could deliver outcomes by maintaining high levels of source population genetic diversity and freeing economic resources to develop ex situ programs for a greater number of threatened amphibian species.

Amphibian reproductive technologies: approaches and welfare considerations

Captive breeding and reintroduction programs have been established for several threatened amphibian species globally, but with varied success. This reflects our relatively poor understanding of the hormonal control of amphibian reproduction and the stimuli required to initiate and complete reproductive events. While the amphibian hypothalamo-pituitary-gonadal (HPG) axis shares fundamental similarities with both teleosts and tetrapods, there are more species differences than previously assumed. 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. 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). Species-dependent methods for handling, restraint and hormone administration (including route and frequency) are discussed to ensure optimal welfare of captive breeding stock. 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). Further research is required to develop hormone therapies for a greater number of species to boost global conservation efforts.

Efficacy of short-term cold storage prior to cryopreservation of spermatozoa in a threatened lizard

Assisted reproductive technologies (ARTs) have a significant role to play in reptile conservation, yet are severely lacking. Previous attempts to cryopreserve spermatozoa in the threatened lizard Varanus panoptes achieved approximately 48% motile sperm post-thaw for samples frozen immediately after collection. However, the feasibility of extended cold storage before cryopreservation has not been tested. We held V. panoptes spermatozoa at either 25°C or 4°C for 8 days, assessing sperm motility at days 1, 2, 4 and 8. Subsamples were cryopreserved on days 1 and 4 following the previously reported protocol for this species. Percentage motility decreased rapidly at 25°C, but did not decrease significantly until 4 days after collection at 4°C, with >30% motility maintained after 8 days. There was no significant difference in post-thaw motility or viability of samples cryopreserved after 1 or 4 days storage at 4°C, yielding substantial results for both parameters (mean motility 23.8% and 28.1% and mean viability 50.1% and 57.5% after 1 and 4 days respectively). We demonstrate the capacity to extend sperm viability for up to 8 days in unfrozen samples and to produce acceptable post-thaw motility in samples frozen after 4 days of storage, contributing to the development of valuable ARTs for lizards and other reptiles.

Efficacy of hormone stimulation on sperm production in an alpine amphibian (Anaxyrus boreas boreas) and the impact of short-term storage on sperm quality

The Southern Rocky Mountain boreal toad (Anaxyrus boreas boreas) has disappeared from much of its range in the alpine regions of Central and Western North America, and restoration efforts are compromised by limited knowledge of this species' reproductive biology. This study aimed to establish whether assisted reproductive techniques could be used to improve breeding output in captive boreal toads by determining the most effective concentration of human chorionic gonadotropin (hCG) for induction of spermiation and viability of sperm during cold storage. Male toads (n = 21) were treated with a Low (3 IU g^-1), Medium (10 IU g^-1), or High (15 IU g^-1) concentration of hCG and spermic urine samples were collected over 24 hrs. Treatment effectiveness was evaluated by measuring the response rate, Total Motility (TM), Forward Progressive Motility (FPM), Quality of FPM (QFPM), and concentration. For short-term cold storage, spermic urine samples (n = 13) were stored at 4 °C for 14 days and sperm TM and FPM monitored daily. All treatments induced spermiation; however, a greater number of toads produced sperm in the Medium and High treatments compared to the Low. Overall, TM, FPM, QFPM and sperm concentration were similar across all three treatments, but variation existed in the timing and duration of peak sperm production. Sperm motility was maintained for up to 14 days in cold storage, although the quality slowly decreased over time. An effective reproduction strategy for the boreal toad will provide a means to improve captive breeding efforts and increase our understanding of the reproductive physiology of alpine Bufonids.

Hormone-induced ovulation and artificial fertilisation in four terrestrial-breeding anurans

The development and application of reproductive technologies has great potential to enhance the conservation management of threatened amphibians globally. The present study quantified the efficacy of protocols previously developed for Pseudophryne guentheri for hormonally inducing egg release and artificial fertilisation in three additional terrestrial-breeding species of Australian ground frog; namely Pseudophryne bibronii , Pseudophryne coriacea and Heleioporus eyrei . Females of each species were administered a priming dose of 0.4µg g-1 of gonadotropin-releasing hormone analogue (GnRHa), followed by an ovulatory dose of 2µg g-1 GnRHa. Egg release was achieved in all species (response 94.7-100%), but early embryo survival differed significantly, ranging from 23.8% to 89.3%. Overall, the protocols were considered effective in P. guentheri , P. bibronii and P. coriacea , but further protocol refinement is required for H. eyrei .

Sperm collection and storage for the sustainable management of amphibian biodiversity

Current rates of biodiversity loss pose an unprecedented challenge to the conservation community, particularly with amphibians and freshwater fish as the most threatened vertebrates. An increasing number of environmental challenges, including habitat loss, pathogens, and global warming, demand a global response toward the sustainable management of ecosystems and their biodiversity. Conservation Breeding Programs (CBPs) are needed for the sustainable management of amphibian species threatened with extinction. CBPs support species survival while increasing public awareness and political influence. Current CBPs only cater for 10% of the almost 500 amphibian species in need. However, the use of sperm storage to increase efficiency and reliability, along with an increased number of CBPs, offer the potential to significantly reduce species loss. The establishment and refinement of techniques over the last two decades, for the collection and storage of amphibian spermatozoa, gives confidence for their use in CBPs and other biotechnical applications. Cryopreserved spermatozoa has produced breeding pairs of frogs and salamanders and the stage is set for Lifecycle Proof of Concept Programs that use cryopreserved sperm in CBPs along with repopulation, supplementation, and translocation programs. The application of cryopreserved sperm in CBPs, is complimentary to but separate from archival gene banking and general cell and tissue storage. However, where appropriate amphibian sperm banking should be integrated into other global biobanking projects, especially those for fish, and those that include the use of cryopreserved material for genomics and other research. Research over a broader range of amphibian species, and more uniformity in experimental methodology, is needed to inform both theory and application. Genomics is revolutionising our understanding of biological processes and increasingly guiding species conservation through the identification of evolutionary significant units as the conservation focus, and through revealing the intimate relationship between evolutionary history and sperm physiology that ultimately affects the amenability of sperm to refrigerated or frozen storage. In the present review we provide a nascent phylogenetic framework for integration with other research lines to further the potential of amphibian sperm banking.

A model protocol for the cryopreservation and recovery of motile lizard sperm using the phosphodiesterase inhibitor caffeine

Reproductive technologies such as genome storage and assisted reproduction have a significant role to play in ending or reversing species extinctions. However, such technologies for non-model organisms (i.e. non-mammalian species) are poorly developed. This is particularly true for the reptiles, in which there is a dearth of successful protocols for cryopreserving reptile spermatozoa, despite limited attempts. We investigated sperm cryopreservation in the Australian lizard Varanus panoptes with the objective of addressing the unmet need for an optimized cryopreservation protocol for the spermatozoa of squamate reptiles. We tested the efficacy of two cryoprotectants [dimethyl sulfoxide (DMSO) and glycerol] as well supplementation with a phosphodiesterase inhibitor (caffeine) to promote post-thaw motility. For cryopreservation, sperm were cooled in straws suspended in liquid nitrogen vapour for 5 minutes (approximately -135°C), before being plunged into liquid nitrogen (approximately -196°C), and later thawed in a water bath at 35°C. Samples were incubated post-thaw for 10 minutes in the presence or absence of 10 mM of caffeine. Both cryoprotectant type and concentration significantly affected percent sperm motility pre-freezing, with DMSO being less cytotoxic than glycerol and motility decreasing at higher concentrations of both cryoprotectant types. While cold shock did not significantly affect sperm motility, both cryoprotectant type and concentration did significantly impact the motility of post-thawed spermatozoa. Thus, mid-range concentrations (10% v/v) of DMSO and glycerol yielded a greater post-thaw motility compared with 5 and 20% v/v, while DMSO proved superior to glycerol. The addition of caffeine resulted in a significant recovery of post-thaw motility for both cryoprotectants, with higher rates of motility being associated with higher cryoprotectant concentrations. These protocols provide a significant step forward for in situ and ex situ management of threatened reptiles and add to recent evidence that reptilian sperm may have the full range of phosphorylation-mediated cellular mechanisms associated with capacitation, motility and metabolic regulation found in mammalian sperm.

Paradoxical population resilience of a keystone predator to a toxic invasive species

Abstract ContextThe invasive cane toad (Rhinella marina) has decimated populations of a keystone predator, the yellow-spotted monitor (Varanus panoptes), causing trophic cascades in Australian animal communities. Paradoxically, some V. panoptes populations coexist with toads. Demonstrating patterns in heterogeneous population-level impacts could reveal mechanisms that mediate individual effects, and provide managers with the ability to predict future impacts and assist in population recovery. AimsThe aim of the present study was to search for spatial patterns of population resilience of V. panoptes to invasive cane toads. MethodsPublished literature, unpublished data, reports and anecdotal information from trained herpetologists were used to test the emerging hypothesis that resilient predator populations are mainly coastal, whereas non-resilient populations are mostly inland. Key resultsPost-toad invasion data from 23 V. panoptes populations supported the idea that toad impacts on V. panoptes were heterogeneous; roughly half the populations could be designated as resilient (n=13) and half as non-resilient (n=10). Resilient populations had longer times since toad invasion than did non-resilient populations (39 versus 9 years respectively), supporting the idea that some recovery can occur. Non-resilient populations were exclusively inland (n=10), whereas resilient populations were split between inland (n=5) and coastal (n=8) populations. Resilient inland populations, however, were mainly confined to areas in which decades had passed since toad invasion. ConclusionsThe findings suggest that coastal V. panoptes populations fare much better than inland populations when it comes to surviving invading cane toads. ImplicationsUnambiguous recovery of monitor populations remains undemonstrated and will require long-term population monitoring before and after toad invasion.

The effect of injection and topical application of hCG and GnRH agonist to induce sperm-release in the roseate frog, Geocrinia rosea

Reproductive technologies may assist amphibian conservation breeding programs (CBPs) to achieve propagation targets and genetic management goals. However, a trial-and-error approach to protocol refinement has led to few amphibian CBPs routinely employing reproductive technologies with predictable outcomes. Additionally, while injections can be safely administered to amphibians, perceived animal welfare risks, such as injury and disease transmission, warrant the development of alternative hormone administration protocols. The present study investigated the spermiation response of roseate frogs, Geocrinia rosea, administered various doses of human chorionic gonadotropin (hCG) and gonadotropin-releasing hormone agonist (GnRH-a) via subcutaneous injection. This study also quantified the spermiation response of frogs administered both hormones via topical application. Total sperm, sperm concentration and sperm viability were assessed over a 12-h period post hormone administration. Males released sperm in response to the injection of hCG (88-100% response; 5, 10 or 20 IU), but all samples collected from males administered hCG topically (100, 100 + DMSO or 200 IU hCG) were aspermic. In contrast, males consistently released sperm in response to both the injection (100% response; 1, 5 or 10 μg), or topical application (80-100% response; 50, 50 + DMSO or 100 μg) of GnRH-a. Overall, the administration of GnRH-a was more effective at inducing spermiation than hCG. Mean total sperm and sperm concentration were highest in response to the optimal topically applied dose of 100 μg GnRH-a (mean total sperm = 2.44 × 10³, sperm concentration = 1.48 × 10⁵ sperm/ml). We provide novel evidence that topical application provides a viable alternative to injection for the administration of GnRH-a to induce spermiation in amphibians.

Hormone-induced sperm-release in the critically endangered Booroolong frog (Litoria booroolongensis): effects of gonadotropin-releasing hormone and human chorionic gonadotropin

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.

Amphibian Assisted Reproductive Technologies: Moving from Technology to Application

Amphibians have experienced a catastrophic decline since the 1980s driven by disease, habitat loss, and impacts of invasive species and face ongoing threats from climate change. About 40% of extant amphibians are under threat of extinction and about 200 species have disappeared completely. Reproductive technologies and biobanking of cryopreserved materials offer technologies that could increase the efficiency and effectiveness of conservation programs involving management of captive breeding and wild populations through reduced costs, better genetic management and reduced risk of species extinctions. However, there are relatively few examples of applications of these technologies in practice in on-the-ground conservation programs, and no example that we know of where genetic diversity has been restored to a threatened amphibian species in captive breeding or in wild populations using cryopreserved genetic material. This gap in the application of technology to conservation programs needs to be addressed if assisted reproductive technologies (ARTs) and biobanking are to realise their potential in amphibian conservation. We review successful technologies including non-invasive gamete collection, IVF and sperm cryopreservation that work well enough to be applied to many current conservation programs. We consider new advances in technology (vitrification and laser warming) of cryopreservation of aquatic embryos of fish and some marine invertebrates that may help us to overcome factors limiting amphibian oocyte and embryo cryopreservation. Finally, we address two case studies that illustrate the urgent need and the opportunity to implement immediately ARTs, cryopreservation and biobanking to amphibian conservation. These are (1) managing the biosecurity (disease risk) of the frogs of New Guinea which are currently free of chytridiomycosis, but are at high risk (2) the Sehuencas water frog of Bolivia, which until recently had only one known surviving male.

Generation of a sexually mature individual of the Eastern dwarf tree frog, Litoria fallax, from cryopreserved testicular macerates: proof of capacity of cryopreserved sperm derived offspring to complete development

Amphibians are the most threatened vertebrate class globally based on recent rates of decline and extinction. Sperm cryopreservation and other assisted reproductive technologies have the potential to help manage small and threatened populations and prevent extinctions. There are a growing number of reports of recovery of amphibian sperm after cryopreservation, but relatively few published reports of amphibian embryos generated from frozen sperm developing beyond metamorphosis to the adult stage and achieving sexual maturation. In this study on the Eastern dwarf tree frog (Litoria fallax), a temperate amphibian species from eastern Australia, a small number of viable metamorphs and one sexually mature male frog (itself producing sperm) were produced from cryopreserved sperm, demonstrating the capacity of embryos generated from cryopreserved sperm to complete the life cycle to sexual maturity. Low progression rates between developmental stages were not deemed to be due to effects of cryopreservation, since control embryos from unfrozen sperm had a similarly low progression rate through development.