Applying cryopreservation to anuran conservation biology

The case for considering the term 'mitochondrial vesicle' as a misnomer in publications about assisted reproductive technologies (ART) for amphibians

The term 'mitochondrial vesicle' was first used in 2003 in a description of anuran sperm and persists to this day throughout the literature on assisted reproductive technologies (ART) for amphibians. In the present paper, we argue that the term is inappropriate because the widely accepted definition of a 'vesicle' refers to an integral structure with an enclosing lipid bilayer/membrane. Moreover, there are no electron micrographs that show a vesicular structure encapsulating mitochondria on amphibian sperm heads in the literature. In fact, in 1993, the mitochondria in the anuran sperm head had been described as positioned in 'mitochondrial collars' or 'mitochondrial sheaths' surrounded by the plasma membrane of the sperm head. On the other hand, mitochondrial-derived vesicles are defined as vesicles shed from mitochondria surfaces, potentially creating confusion. Therefore, our view is that the term 'mitochondrial vesicle' should be avoided in describing the positioning of mitochondria on sperm.

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.

Development of an amphibian sperm biobanking protocol for genetic management and population sustainability

Sperm cryopreservation is a vital tool in amphibian assisted reproductive technologies that aids in genetic and population management, specifically for at-risk species. Significant advancements have been made in the cryopreservation of amphibian sperm, yet there is little information on how the cryopreservation process influences fertilization and embryonic development. In this study, we tested several cryoprotective agents (CPAs) and freezing rates on sperm recovery, fertilization potential and embryo development using Fowler's toads (Anaxyrus fowleri) as a model amphibian species for application to at-risk anurans. Three cryoprotectant treatments were tested, which included 10% trehalose + 0.25% bovine serum albumin with (1) 5% N,N-dimethylformamide (DMFA); (2) 10% DMFA; or (3) 10% dimethyl sulfoxide (DMSO). Additionally, sperm in each cryoprotectant was frozen at two different rates, -32 to -45°C/min and -20 to -29°C/min. Post-thaw sperm analysis included motility, morphology, viability, fertilization success and embryo development. Results show that 10% DMFA produced significantly higher (P = 0.005) post-thaw sperm motility than 5% DMFA and was similar to 10% DMSO. Furthermore, sperm frozen at -32 to -45°C/min had significantly higher post-thaw motility (P < 0.001) compared to sperm frozen at -20 to -29°C/min. We also found that embryos fertilized with sperm frozen with 5% DMFA resulted in significantly higher (P = 0.02) cleavage than 10% DMSO, yet there was no other effect of CPA on fertilization or embryo development. Furthermore, embryos fertilized with sperm frozen at -32 to -45°C/min resulted in significantly higher cleavage (P = 0.001), neurulation (P = 0.001) and hatching (P = 0.002) numbers than sperm frozen at a rate of -20 to -29°C/min. Overall, eggs fertilized with frozen-thawed sperm produced 1327 tadpoles. These results provide insight towards a biobanking strategy that can be applied to imperilled species to preserve genetic lineages and bolster offspring genetic diversity for reintroduction.

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.

First natural breeding of the endangered dusky gopher frog (Lithobates sevosus) in captivity

To date, all captive breeding of the dusky gopher frog, Lithobates sevosus, a federally listed endangered species, has been accomplished using in vitro fertilization (IVF). Here, we describe multievent and highly fecund captive reproduction of dusky gopher frogs driven solely by natural environmental factors. Six pairs of L. sevosus were kept in a 3.7 × 4.4 m² outdoor enclosure designed to resemble their natural breeding habitat, which included a pool and three artificial burrows. Modifications to the enclosure that simulated temperatures and conditions within their natural range during winter were added in October and removed in late February. Following a warm, rainy period, five egg masses were laid between March 5 and 11, 2020. The number of oocytes per egg mass was 2300 ± 409 (range = 1341–3565), with the total across all five egg masses being 11,501. Of these oocytes, the hatching rate was 68.58 ± 10.05% (range = 37.53%–95.59%), with a total of 7887 successful hatchlings overall. Clutch sizes were similar to those in the wild and greater than those typically produced using IVF; thus, natural breeding can substantially increase the number of frogs available for reintroduction programs. Although assisted reproductive technologies such as IVF will continue to be useful for ensuring the success of strategic genetic pairings of captive L. sevosus, the new tool of nonassisted reproduction in specifically designed outdoor enclosures is an important advancement for the conservation and recovery of this endangered species.

The first captive breeding of the dusky gopher frog, Lithobates sevosus, triggered by environmental factors rather than assisted laboratory technologies is reported. Natural breeding increased recruitment into captive and in situ populations.

The ART of bringing extinction to a freeze - History and future of species conservation, exemplified by rhinos

The ongoing mass extinction of animal species at an unprecedented rate is largely caused by human activities. Progressive habitat destruction and fragmentation is resulting in accelerated loss of biodiversity on a global scale. Over decades, captive breeding programs of non-domestic species were characterized by efforts to optimize species-specific husbandry, to increase studbook-based animal exchange, and to improve enclosure designs. To counter the ongoing dramatic loss of biodiversity, new approaches are warranted. Recently, new ideas, particularly the application of assisted reproduction technologies (ART), have been incorporated into classical zoo breeding programs. These technologies include semen and oocyte collection, artificial insemination, and in-vitro embryo generation. More futuristic ideas of advanced ART (aART) implement recent advances in biotechnology and stem-cell related approaches such as cloning, inner cell mass transfer (ICM), and the stem-cell-associated techniques (SCAT) for the generation of gametes and ultimately embryos of highly endangered species, such as the northern white rhinoceros (Ceratotherium simum cottoni) of which only two female individuals are left. Both, ART and aART greatly depend on and benefit from the rapidly evolving cryopreservation techniques and biobanking not only of genetic, but also of viable cellular materials suitable for the generation of induced pluripotent stem cells (iPSC). The availability of cryopreserved materials bridges gaps in time and space, thereby optimizing the available genetic variability and enhancing the chance to restore viable populations.