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

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.

Male Cope's gray treefrogs (Hyla chrysoscelis) in amplexus have elevated and correlated steroid hormones compared to solitary males

Gonadal steroid hormones are typically elevated during the breeding season-a finding known as an associated reproductive pattern. Though less studied, there is also evidence, in both sexes, for elevated adrenal/interrenal steroids, including acute elevations on the day of mating. I investigated gonadal and interrenal steroids in wild male Cope's gray treefrogs at breeding aggregations. I collected blood from males found in amplexus with female mates (amplexed males) and males sampled at the same time and location that were actively advertising vocally and without a mate (solo males). Concentrations of plasma corticosterone, testosterone, and 17β-estradiol (CORT, T and E2, respectively) were validated and measured. These two categories of males differed in four ways: (1) amplexed males exhibited significantly elevated concentrations of all three steroids compared to solo males (CORT: +347 %; T: +60 %; and E2: +43 %); (2) these hormone profiles alone accurately predicted male mating category with ca. 83 % accuracy using a discriminant function analysis; (3) amplexed males exhibited significant between-hormone correlations (T and E2 were positively correlated and CORT and E2 were negatively correlated) whereas no correlations were found in solo males; (4) amplexed males showed a negative correlation with CORT concentration and the time of night, whereas no such pattern was present in solo males. These findings suggest an acute and strong coactivation of the interrenal and gonadal axes that could drive phenotypic integration during this fitness-determining moment. I discuss these findings and suggest experiments to determine causation, including the role of motor behavior driving endocrine states and the role of female selection on endocrine profiles.

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.

Gamete Collection, Artificial Fertilization and Captive-Rearing of Eggs in a Terrestrial-Breeding Anuran with Parental Care: Alytes obstetricans

The genus Alytes consists of six primitive terrestrial-breeding species (five of them endangered or present in restricted distributions) with unique male parental care. Alytes obstetricans was used as a model for the development of assisted reproductive technologies for gamete collection, artificial fertilization and captive-rearing of embryos. Sperm collection was achieved with human chorionic gonadotropin (hCG), but only 17 to 50% of males responded to the hormone. In addition, an effect of captivity on sperm quality was observed. A combination of gonadotropin-releasing hormone agonist (GnRHa) and hCG was tested for induction of ovulation, and 100% of females responded to the treatment. Recently collected sperm was used in artificial fertilization, and 10% of eggs showed complete embryo development. To design a method for captive-rearing of embryos, natural clutches (n = 13) were removed from males and divided into two sub-clutches. One was kept with all eggs together and in the other, the egg string was cut and eggs were split individually. All sub-clutches with eggs kept separated presented embryo survival (ranging from 27 to 61%) that hatched normally, while only one sub-clutch with embryos maintained together had some embryo survival (36%). These results may contribute to the management of this and related 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.

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.

Spermiation response to exogenous hormone therapy in hibernated and non-hibernated boreal toads (Anaxyrus boreas boreas)

Conservation programs for threatened high- elevation amphibian species rely on hibernation to trigger appropriate male reproductive behaviours and gametogenesis. Although common practice and anecdotal observations have supported the practice of hibernation, there is limited empirical evidence documenting the effects on reproduction in these species. In this study, the effect of hibernation on sperm quantity and quality was evaluated for the alpine species Anaxyrus boreas boreas. Hibernated (n=19) and non-hibernated (n=21) male toads were administered 10IUg-1 body weight (BW) human chorionic gonadotropin (hCG) and spermic urine was collected over 24h. Hibernation had no effect on the number of males undergoing spermatogenesis, but hibernated males produced sperm in higher concentrations. Sperm quality was measured in terms of total motility, forward progressive motility and quality of forward progression. Although there was no difference in the total sperm motility of samples from hibernated and non-hibernated toads, the percentage of sperm exhibiting forward progressive motility and the quality of forward progression was significantly greater from hibernated toads. These results support our hypothesis that hibernation impacts both sperm quantity and quality in male boreal toads. This study will better inform captive breeding management decisions for threatened alpine species, in imminent danger of extinction.

Hormone treatment does not reliably induce spermiation or mating in Hamilton

Amidst a global amphibian decline, captive breeding has become an important component of many conservation management programs. Some species fail to readily reproduce in captivity, including leiopelmatid frogs, an archaic lineage endemic to New Zealand. Assisted reproductive technologies can improve the reproductive potential and genetic management of captive programs. Herein we describe efforts to induce spermiation and mating in the threatened Hamilton's frog Leiopelma hamiltoni using a gonadotrophin-releasing hormone agonist and human chorionic gonadotrophin. The spermiation response was poor, with few individuals releasing spermatozoa and a low sperm concentration (mean (±s.e.) 27.4±8.5×103 spermatozoa mL-1) when spermiation was stimulated. The sperm concentration peaked 12-24h after hormone administration, suggesting this species may be slower to react than other anurans. Spermic urine was present in five males before hormone treatment. The sperm concentration was higher in this group (128.7±54.9×103 spermatozoa mL-1) than in the hormone-induced males. All spermatozoa observed exhibited no motility or, at most, a limited swaying movement with no forward progression. In separate hormone induction trials with 60 individuals (two males to one female per trial), no mating was exhibited during the 12h after treatment. Further studies to hormonally stimulate gamete release and mating are needed in leiopelmatids.

Using reproductive technologies to assess the development of secondary sexual characteristics, ovarian senescence and hermaphroditism in the endangered mountain yellow-legged frog Rana muscosa

Anurans can display a host of intriguing sexual syndromes, including hermaphroditism and sex reversal. Using a multifaceted approach for diagnosing and characterising hermaphroditism in the endangered anuran species Rana mucosa , we tracked changes in female reproductive status using hormone monitoring, ultrasound examinations, individual life history, fertilisation records and post-mortem findings. Seven individuals originally sexed as females developed secondary male sexual characteristics, behaviour and hormone profiles and, in some cases, had testicular tissue despite having previously laid eggs. Our results suggest that reproductive technologies can shed light on life history patterns and reproductive anomalies that may affect endangered anuran survival.

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 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.

Excreted testosterone and male sexual proceptivity: A hormone validation and proof-of-concept experiment in túngara frogs

Conventional methods for sampling hormones often preclude strong inference experimental designs, including repeated measures of both hormones and behavior and balanced or simultaneous designs for hormone-behavior sampling. In amphibians there is an opportunity to non-invasively and repeatedly sample excreted steroids in the water. We examined testosterone (T) in túngara frogs (Physalaemus (=Engystomops) pustulosus) using minimally invasive water-borne methods. First, we validated procedures for the collection, extraction and measurement of T in adult males and females using pharmacological challenges coupled with estimates of parallelism and recovery determination. Next, we extended the timeline of sampling over 9 days in order to evaluate the kinetics of excretion (baseline phase, challenge phase, recovery phase), including the estimation of individual differences during baseline sampling. We also estimated concentrations of creatinine (Cr) in each water sample and evaluated whether correcting for this proxy of urine concentration significantly decreased error variance in T estimates. Lastly, we incorporated a standardized and repeated measures assay of male sexual proceptivity (phonotaxis) during the predicted peak T and recovery T timepoints. We found strong evidence supporting the utility of these methods for precise, biologically informative estimates of T in both sexes. Males had higher T than females and responded to pharmacological challenges by elevating T substantially within 48 h of challenge (hCG, GnRH). Males exhibited repeatability in baseline T and phonotaxis frequencies were positively associated with higher T. Adjusting T levels for the simultaneous measure of Cr significantly improved model fit, which in conjunction with marked variation in urine concentration, suggests that urine likely serves as the major source of excreted T. In summary, this proof-of-concept and methods study demonstrates the utility and accuracy of measuring water-borne T and behavior in amphibians.

Evaluating amphibian biobanking and reproduction for captive breeding programs according to the Amphibian Conservation Action Plan objectives

The Amphibian Conservation Action Plan (ACAP), published in 2007, is a formal document of international significance that proposed eleven relevant actions for global amphibian conservation. Action seven of the ACAP document addresses the use of amphibian captive programs as a conservation tool. Appendix material under this action explores the potential use of Genome Resource Banking (biobanking) as an urgently needed tool for these captive programs. ACAP proposed twelve objectives for Genome Resource Banking which exhibit little emphasis on reproduction as a vital underlying science for amphibian Captive Breeding Programs (CBP's). Here we have reassessed the original twelve ACAP objectives for amphibian reproduction and biobanking for CBP's as a contribution to future ACAP review processes. We have reviewed recent advances since the original objectives, as well as highlighted weaknesses and strengths for each of these objectives. We make various scientific, policy and economic recommendations based on the current reality and recent advances in relevant science in order to inform future ACAP towards new global objectives. The number of amphibian CBP'S has escalated in recent years and reproductive success is not always easily accomplished. Increases in applied and fundamental research on the natural history and reproductive biology of these species, followed by the appropriate development and application of artificial reproductive technologies (ART's) and the incorporation of genome resource banks (GRB's), may turn CBP's into a more powerful tool for amphibian conservation.

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.

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.

Evaluation of different temporal periods between hormone-induced ovulation attempts in the female Fowler's toad Anaxyrus fowleri

Many amphibian species reinitiate the processes of preparing for reproduction (e.g. oogenesis) soon after breeding indicating hormone-induced ovulation could potentially be achieved out-of-season, which would lead to higher annual fecundity compared to mono-seasonal breeding. Such strategies would be beneficial to captive breeding programs for threatened species that are short-lived, have aging populations or need large numbers of offspring to meet reintroduction goals for species recovery. Unfortunately, little is known regarding how female anurans respond to multiple ovulation events within a year, which could lead to higher annual fecundity compared to mono-seasonal breeding. Thus, we evaluated the effect of temporal period between exogenous hormone stimulation events on egg production using the Fowler's toad Anaxyrus fowleri as a model species. Female toads (n = 21) were administered hormone therapy twice in 1 year with toads randomly assigned to a treatment of either a 4-, 8- or 12-month recovery period between hormone stimulations. Ovulation was induced using two priming doses of human chorionic gonadotropin (100 IU; hCG) 72 h apart, followed by a resolving dose of hCG (500 IU) plus gonadotropin releasing hormone analogue (GnRHa; 15 μg) given 24 h after the second priming injection. Measured response variables include the number of females ovulating after treatment, total number of eggs produced and percent fertilization, neurula and tadpole development. No significant treatment effects were observed for any response variable (P > 0.05). Findings from this study suggest that hormone therapy can be administered in a bufonid species every 4 or 8 months without significantly affecting the number of ovulating females, egg production, fertilization, neurulation or tadpole development. By collecting gametes out-of-season or multiple times throughout the year, captive breeding programs could potentially increase tadpole production for reintroductions as well as extend the breeding window in captivity.

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.