Recent advances and prospects in germplasm preservation of rare and endangered species

Fertility preservation strategies using cryopreservation have enormous potential for helping sustain and protect rare and endangered species, especially to assist managing or 'rescuing' the genomes of genetically valuable individuals. However, wide-scale applications are still limited by significant physiological variations among species and a sheer lack of fundamental knowledge about basic reproductive traits as well as in germplasm cryobiology. Cryo-studies have been conducted in more species (mainly vertebrates) in the recent years but a vast majority still remains un-studied. Semen cryopreservation represents the most extensive effort with live births reported in more and more species after artificial insemination. Oocyte freezing remains challenging and unsuccessful in wild species and will require more research before becoming a standard procedure. As an alternative to fully grown gametes, gonadal tissue preservation has become a promising option in vertebrates. Yet, more fertility preservation options are necessary to save species so a change in strategy might be required. It is worthwhile thinking beyond systematic characterizations and considering the application of cutting edge approaches to universally preserve the fertility of a vast array of species.

Non-invasive reproductive and stress endocrinology in amphibian conservation physiology

Non-invasive endocrinology utilizes non-invasive biological samples (such as faeces, urine, hair, aquatic media, and saliva) for the quantification of hormones in wildlife. Urinary-based enzyme immunoassay (EIA) and radio-immunoassay have enabled the rapid quantification of reproductive and stress hormones in amphibians (Anura: Amphibia). With minimal disturbance, these methods can be used to assess the ovarian and testicular endocrine functions as well as physiological stress in captive and free-living populations. Non-invasive endocrine monitoring has therefore greatly advanced our knowledge of the functioning of the stress endocrine system (the hypothalamo-pituitary-interrenal axis) and the reproductive endocrine system (the hypothalamo-pituitary-gonadal axis) in the amphibian physiological stress response, reproductive ecology, health and welfare, and survival. Biological (physiological) validation is necessary for obtaining the excretory lag time of hormone metabolites. Urinary-based EIA for the major reproductive hormones, estradiol and progesterone in females and testosterone in males, can be used to track the reproductive hormone profiles in relationship to reproductive behaviour and environmental data in free-living anurans. Urinary-based corticosterone metabolite EIA can be used to assess the sublethal impacts of biological stressors (such as invasive species and pathogenic diseases) as well as anthropogenic induced environmental stressors (e.g. extreme temperatures) on free-living populations. Non-invasive endocrine methods can also assist in the diagnosis of success or failure of captive breeding programmes by measuring the longitudinal patterns of changes in reproductive hormones and corticosterone within captive anurans and comparing the endocrine profiles with health records and reproductive behaviour. This review paper focuses on the reproductive and the stress endocrinology of anurans and demonstrates the uses of non-invasive endocrinology for advancing amphibian conservation physiology. It also provides key technical considerations for future research that will increase the accuracy and reliability of the data and the value of non-invasive endocrinology within the conceptual framework of conservation physiology.

Investigating patterns in the spermiation response of eight Australian frogs administered human chorionic gonadotropin (hCG) and luteinizing hormone-releasing hormone (LHRHa)

Exogenous LHRHa and hCG are routinely employed to induce spermiation in vivo in anurans. To date, however, few studies have directly compared the efficacy of these two hormones. The aim of this study was threefold. First to quantify the spermiation response of eight Australian anuran species (Crinia glauerti, Crinia georgiana, Crinia pseudinsignifera, Geocrinia rosea, Heleioporus albopunctatus, Heleioporuseyrei, Neobatrachus pelobatoides and Pseudophryne guentheri) administered LHRHa and hCG. Second, to determine whether variance in spermiation responses is related to a species' reproductive mode (aquatic vs. terrestrial) or family (Limnodynastidae vs. Myobatrachidae). Third, to compare the quantity and quality of spermatozoa obtained via hormone administration (LHRHa and hCG) to spermatozoa obtained via testis removal and maceration. There was no significant difference in the viability of spermatozoa obtained from hCG or LHRHa administration in any of the eight study species. The sperm viability of samples ranged from 28-84% in C. georgiana and G. rosea, respectively. The hormone that induced the release of the highest number of spermatozoa differed among species, with all five species belonging to the family Myobatrachidae responding better to LHRHa, and the three species from the family Lymnodynastidae releasing a greater number of spermatozoa in response to hCG. Importantly, these results provide the first preliminary evidence that hCG and LHRHa efficacy in anurans may be predicted by phylogeny. Understanding such broad-scale patterns in the response of anurans to exogenous hormones will expedite the application of assisted reproductive technologies to novel species.

Optimisation of an oviposition protocol employing human chorionic and pregnant mare serum gonadotropins in the barred frog Mixophyes fasciolatus (Myobatrachidae)

BACKGROUND

Protocols for the hormonal induction of ovulation and oviposition are essential tools for managing threatened amphibians with assisted reproduction, but responses vary greatly between species and even broad taxon groups. Consequently, it is necessary to assess effectiveness of such protocols in representative species when new taxa become targets for induction. The threatened genus Mixophyes (family Myobatrachidae) has amongst the highest proportion of endangered species of all the Australian amphibians. This study developed and optimised the induction of oviposition in a non-threatened member of this taxon, the great barred frog (Mixophyes fasciolatus).

METHODS

Gravid female M. fasciolatus were induced to oviposit on one or more occasions by administration of human chorionic gonadotropin (hCG) with or without priming with pregnant mare serum gonadotropin (PMSG). Treatments involved variations in hormone doses and combinations (administered via injection into the dorsal lymph sacs), and timing of administration. Pituitary homogenates from an unrelated bufonid species (Rhinella marina) were also examined with hCG.

RESULTS

When injected alone, hCG (900 to 1400 IU) induced oviposition. However, priming with two time dependent doses of PMSG (50 IU, 25 IU) increased responses, with lower doses of hCG (200 IU). Priming increased response rates in females from around 30% (hCG alone) to more than 50% (p = 0.035), and up to 67%. Increasing the interval between the first PMSG dose and first hCG dose from 3 to 6 days also produced significant improvement (p<0.001). Heterologous pituitary extracts administered with hCG were no more effective than hCG alone (p = 0.628).

CONCLUSIONS

This study found that M. fasciolatus is amongst the few amphibian species (including Xenopus (Silurana) and some bufonids) that respond well to the induction of ovulation utilising mammalian gonadotropins (hCG). The optimal protocol for M. fasciolatus involved two priming doses of PMSG (50 IU and 25 IU) administered at 6 and 4 days respectively, prior to two doses of hCG (100 IU), 24 hours apart. This study is also the first to demonstrate in an amphibian species that responds to mammalian gonadotropins that an increase in the ovulation rate occurs after priming with a gonadotropin (PMSG) with FSH activity.

A comparison of human chorionic gonadotropin and luteinizing hormone releasing hormone on the induction of spermiation and amplexus in the American toad (Anaxyrus americanus)

BACKGROUND

Captive breeding programs for endangered amphibian species often utilize exogenous hormones for species that are difficult to breed. The purpose of our study was to compare the efficacy of two different hormones at various concentrations on sperm production, quantity and quality over time in order to optimize assisted breeding.

METHODS

Male American toads (Anaxyrus americanus) were divided into three separate treatment groups, with animals in each group rotated through different concentrations of luteinizing hormone releasing hormone analog (LHRH; 0.1, 1.0, 4.0 and 32 micrograms/toad), human chorionic gonadotropin (hCG; 50, 100, 200, and 300 IU), or the control over 24 hours. We evaluated the number of males that respond by producing spermic urine, the sperm concentration, percent motility, and quality of forward progression. We also evaluated the effects of hCG and LHRH on reproductive behavior as assessed by amplexus. Data were analyzed using the Generalized Estimating Equations incorporating repeated measures over time and including the main effects of treatment and time, and the treatment by time interaction.

RESULTS

The hormone hCG was significantly more effective at stimulating spermiation in male Anaxyrus americanus than LHRH and showed a dose-dependent response in the number of animals producing sperm. At the most effective hCG dose (300 IU), 100% of the male toads produced sperm, compared to only 35% for the best LHRH dose tested (4.0 micrograms). In addition to having a greater number of responders (P < 0.05), the 300 IU hCG treatment group had a much higher average sperm concentration (P < 0.05) than the treatment group receiving 4.0 micrograms LHRH. In contrast, these two treatments did not result in significant differences in sperm motility or quality of forward progressive motility. However, more males went into amplexus when treated with LHRH vs. hCG (90% vs. 75%) by nine hours post-administration.

CONCLUSION

There is a clear dichotomy between the two hormones' physiological responses on gamete production and stimulation of amplexus. Understanding how these two hormones influence physiology and reproductive behaviors in amphibians will have direct bearing on establishing similar breeding protocols for endangered species.

Comparative cryobiological traits and requirements for gametes and gonadal tissues collected from wildlife species

A major challenge to retaining viability of frozen gametes and reproductive tissues is to understand and overcome species-specificities, especially because there is substantial diversity in cryobiological properties and requirements among cell types and tissues. Systematic studies can lead to successful post-thaw recovery, especially after determining: 1) membrane permeability to water and cryoprotectant, 2) cryoprotectant toxicity, 3) tolerance to osmotic changes, and 4) resistance to cooling and freezing temperatures. Although species-dependency ultimately dictates the ability of specific cells and tissues to survive freeze-thawing, there are commonalities between taxa that allow a protocol developed for one species to be useful information for another. This is the reason for performing comparative cryopreservation studies among diverse species. Our laboratory has compared cellular cryotolerance, especially in spermatozoa, in a diverse group of animals-from corals to elephants-for more than 30 yrs. Characterizing the biophysical traits of gametes and tissues is the most efficient way to develop successful storage and recovery protocols, but, such data are only available for a few laboratory, livestock, and fish species, with virtually all others (wild mammals, birds, reptiles, and amphibians) having gone unstudied. Nonetheless, when a rare animal unexpectedly dies, there is no time to understand the fundamentals of biophysics. In these emergencies, it is necessary to rely on experience and the best data from taxonomically-related species. Fortunately, there are some general similarities among most species, which, for example, allow adequate post-thaw viability. Regardless, there is a priority for more information on biophysical traits and freezing tolerance of distinctive biomaterials, especially for oocytes and gonadal tissues, and even for common, domesticated animals. Our colleague, Dr John Critser was a pioneer in cryobiology, earning that moniker because of his advocacy and devotion to understanding the differences (and similarities) among species to better store living genetic material.

Effect of priming injections of luteinizing hormone-releasing hormone on spermiation and ovulation in Gϋnther's toadlet, Pseudophryne guentheri

BACKGROUND

In the majority of vertebrates, gametogenesis and gamete-release depend on the pulsatile secretion of luteinizing hormone-releasing hormone (LHRH) from the hypothalamus. Studies attempting to artificially stimulate ovulation and spermiation may benefit from mimicking the naturally episodic secretion of LHRH by administering priming injections of a synthetic analogue (LHRHa). This study investigated the impact of low-dose priming injections of LHRHa on gamete-release in the Australian toadlet Pseudophryne guentheri.

METHODS

Toadlets were administered a single dose of two micrograms per. gram LHRHa without a priming injection (no priming), or preceded by one (one priming) or two (two priming) injections of 0.4 micrograms per. gram LHRHa. Spermiation responses were evaluated at 3, 7 and 12 hrs post hormone administration (PA), and sperm number and viability were quantified using fluorescent microscopy. Oocyte yields were evaluated by stripping females at 10-11 hrs PA. A sub-sample of twenty eggs per female was then fertilised (with sperm obtained from testis macerates) and fertilisation success determined.

RESULTS

No priming induced the release of the highest number of spermatozoa, with a step-wise decrease in the number of spermatozoa released in the one and two priming treatments respectively. Peak sperm-release occurred at 12 hrs PA for all priming treatments and there was no significant difference in sperm viability. Females in the control treatment failed to release oocytes, while those administered an ovulatory dose without priming exhibited a poor ovulatory response. The remaining two priming treatments (one and two priming) successfully induced 100% of females to expel an entire clutch. Oocytes obtained from the no, or two priming treatments all failed to fertilise, however oocytes obtained from the one priming treatment displayed an average fertilisation success of 97%.

CONCLUSION

Spermiation was most effectively induced in male P. guentheri by administering a single injection of LHRHa without priming. In contrast, female P. guentheri failed to ovulate without priming. A single priming injection induced the release of oocytes of high viability compared to oocytes obtained from females in the two priming treatment which underwent a process of over-ripening.

Hormonal induction of gamete release, and in-vitro fertilisation, in the critically endangered southern corroboree frog, Pseudophryne corroboree

BACKGROUND

Conservation Breeding Programs (CBP's) are playing an important role in the protection of critically endangered anuran amphibians, but for many species recruitment is not successful enough to maintain captive populations, or provide individuals for release. In response, there has been an increasing focus on the use of Assisted Reproductive Technologies (ART), including the administration of reproductive hormones to induce gamete release followed by in vitro fertilisation. The objective of this study was to test the efficacy of two exogenous hormones to induce gamete release, for the purpose of conducting in vitro fertilisation (IVF), in one of Australia's most critically endangered frog species, Pseudophryne corroboree.

METHODS

Male frogs were administered a single dose of either human chorionic gonadotropin (hCG) or luteinizing hormone-releasing hormone (LHRHa), while female frogs received both a priming and ovulatory dose of LHRHa. Spermiation responses were evaluated at 3, 7, 12, 24, 36, 48, 60 and 72 h post hormone administration (PA), and sperm number and viability were quantified using fluorescent microscopy. Ovulation responses were evaluated by stripping females every 12 h PA for 5 days. Once gametes were obtained, IVF was attempted by combining spermic urine with oocytes in a dilute solution of simplified amphibian ringer (SAR).

RESULTS

Administration of both hCG and LHRHa induced approximately 80% of males to release sperm over 72 h. Peak sperm release occurred at 12 h PA for hCG treated males and 36 h PA for LHRHa treated males. On average, LHRHa treated males released a significantly higher total number of live sperm, and a higher concentration of sperm, over a longer period. In female frogs, administration of LHRHa induced approximately 30% of individuals to release eggs. On average, eggs were released between 24 and 48 h PA, with a peak in egg release at 36 h PA. IVF resulted in a moderate percentage (54.72%) of eggs being fertilised, however all resultant embryos failed prior to gastrulation.

CONCLUSIONS

Hormone treatment successfully induced spermiation and ovulation in P. corroboree, but refinement of gamete induction and IVF techniques will be required before ART protocols can be used to routinely propagate this species.

Effects of luteinizing hormone-releasing hormone and arginine-vasotocin on the sperm-release response of Günther's Toadlet, Pseudophryne guentheri

BACKGROUND

Luteinizing hormone-releasing hormone (LHRH) is an exogenous hormone commonly used to induce spermiation in anuran amphibians. Over the past few decades, the LHRH dose administered to individuals and the frequency of injection has been highly variable. The sperm-release responses reported have been correspondingly diverse, highlighting a need to quantify dose-response relationships on a species-specific basis. This study on the Australian anuran Pseudophryne guentheri first evaluated the spermiation response of males administered one of five LHRHa doses, and second, determined whether AVT administered in combination with the optimal LHRHa dose improved sperm-release.

METHODS

Male toadlets were administered a single dose of 0, 1, 2, 4 or 8 micrograms/g body weight of LHRHa. A 4 micrograms/g dose of AVT was administered alone or in combination with 2 micrograms/g LHRHa. Spermiation responses were evaluated at 3, 7 and 12 h post hormone administration (PA), and sperm number and viability were quantified using fluorescent microscopy.

RESULTS

LHRHa administration was highly effective at inducing spermiation in P. guentheri, with 100% of hormone-treated males producing sperm during the experimental period. The number of sperm released in response to 2 micrograms/g LHRHa was greater than all other doses administered and sperm viability was highest in the 1 microgram/g treatment. The administration of AVT alone or in combination with LHRHa resulted in the release of significantly lower sperm numbers.

CONCLUSION

Overall, results from this study suggest that in P. guentheri, LHRHa is effective at inducing spermiation, but that AVT inhibits sperm-release.

Biotransport phenomena in freezing mammalian oocytes

Water transport across the cell plasma membrane and intracellular ice formation (IIF)-the two biophysical events that may cause cell injury during cryopreservation-were studied by cryomicroscopy and modeling using mammalian (Peromyscus) oocytes. Unusually high activation energy for water transport across the cell plasma membrane was identified indicating that the water transport process is unusually sensitive to temperature (and cooling rate). Although literally all studies on IIF were conducted using protocols with ice-seeding (seeding extracellular ice usually at ≥-7 °C), it is not used for cell cryopreservation by vitrification that is becoming increasingly popular today. In this article, we show that ice-seeding has a significant impact on IIF. With ice-seeding and cooling at 60 °C/min, IIF was observed to occur over a wide range from approximately -8 to -48 °C with a clear change of the ice nucleation mechanism (from surface- to volume-catalyzed nucleation) at approximately -43 °C. On the contrary, without ice-seeding, IIF occurred over a much narrower range from approximately -19 to -27 °C without a noticeable change of the nucleation mechanism. Moreover, the kinetics of IIF without ice-seeding was found to be strongly temperature (and cooling rate) dependent. These findings indicate the importance of quantifying the IIF kinetics in the absence of ice-seeding during cooling for development of optimal vitrification protocols of cell cryopreservation.

Lessons from biodiversity--the value of nontraditional species to advance reproductive science, conservation, and human health

Reproduction is quintessential to species survival. But what is underappreciated for this discipline is the wondrous array of reproductive mechanisms among species- variations as diverse as the morphology of the species themselves (more than 55,000 vertebrate and 1.1 million invertebrate types). We have investigated only a tiny fraction of these species in reproductive science. Besides the need to fill enormous gaps in a scholarly database, this knowledge has value for recovering and genetically managing rare species as well as addressing certain reproductive issues in humans. This article provides examples, first to advise against oversimplifying reproduction and then to show how such knowledge can have practical use for managing whole animals, populations, or even saving an entire species. We also address the expected challenges and opportunities that could lead to creative shifts in philosophy and effective actions to benefit more species as well as a future generation of reproductive scientists.

Hormonal induction of spawning in 4 species of frogs by coinjection with a gonadotropin-releasing hormone agonist and a dopamine antagonist

BACKGROUND

It is well known that many anurans do not reproduce easily in captivity. Some methods are based on administration of mammalian hormones such as human chorionic gonadotropin, which are not effective in many frogs. There is a need for simple, cost-effective alternative techniques to induce spawning.

METHODS

Our new method is based on the injection of a combination of a gonadotropin-releasing hormone (GnRH) agonist and a dopamine antagonist. We have named this formulation AMPHIPLEX, which is derived from the combination of the words amphibian and amplexus. This name refers to the specific reproductive behavior of frogs when the male mounts and clasps the female to induce ovulation and to fertilize the eggs as they are laid.

RESULTS

We describe the use of the method and demonstrate its applicability for captive breeding in 3 different anuran families. We tested several combinations of GnRH agonists with dopamine antagonists using Lithobates pipiens. The combination of des-Gly10, D-Ala6, Pro-LHRH (0.4 microrams/g body weight) and metoclopramide (10 micrograms/g BWt. MET) was most effective. It was used in-season, after short-term captivity and in frogs artificially hibernated under laboratory conditions. The AMPHIPLEX method was also effective in 3 Argentinian frogs, Ceratophrys ornata, Ceratophrys cranwelli and Odontophrynus americanus.

CONCLUSION

Our approach offers some advantages over other hormonally-based techniques. Both sexes are injected only once and at the same time, reducing handling stress. AMPHIPLEX is a new reproductive management tool for captive breeding in Anura.