Amphibian reproductive technologies: approaches and welfare considerations

Organization of enkephalinergic neuronal system in the central nervous system of the gecko Hemidactylus frenatus

Enkephalins are endogenous opioid pentapeptides that play a role in neurotransmission and pain modulation in vertebrates. However, the distribution pattern of enkephalinergic neurons in the brains of reptiles has been understudied. This study reports the organization of the methionine-enkephalin (M-ENK) and leucine-enkephalin (L-ENK) neuronal systems in the central nervous system of the gecko Hemidactylus frenatus using an immunofluorescence labeling method. Although M-ENK and L-ENK-immunoreactive (ir) fibers extended throughout the pallial and subpallial subdivisions, including the olfactory bulbs, M-ENK and L-ENK-ir cells were found only in the dorsal septal nucleus. Enkephalinergic perikarya and fibers were highly concentrated in the periventricular and lateral preoptic areas, as well as in the anterior and lateral subdivisions of the hypothalamus, while enkephalinergic innervation was observed in the hypothalamic periventricular nucleus, infundibular recess nucleus and median eminence. The dense accumulation of enkephalinergic content was noticed in the pars distalis of the hypophysis. In the thalamus, the nucleus rotundus and the dorsolateral, medial, and medial posterior thalamic nuclei contained M-ENK and L-ENK-ir fibers, whereas clusters of M-ENK and L-ENK-ir neurons were observed in the pretectum, mesencephalon, and rhombencephalon. The enkephalinergic fibers were also seen in the area X around the central canal, as well as the dorsal and ventral horns. The widespread distribution of enkephalin-containing neurons within the central nervous system implies that enkephalins regulate a variety of functions in the gecko, including sensory, behavioral, hypophysiotropic, and neuroendocrine functions.

Rearing density and food variety impact growth, development, and survival of larvae in the declining amphibian, Pseudacris maculata

Boreal chorus frogs (Pseudacris maculata Agassiz 1850) are a widespread amphibian in North America, but several populations are in decline. Specifically, we are developing captive breeding and reintroduction methods for the Great Lakes/St. Lawrence-Canadian Shield population. Here we present the effects of tadpole density, food variety, and addition of supplemental minerals to rearing water on the growth, development, and survival during the larval and metamorph/juvenile stages. We conducted two experiments using a factorial design. We found that low tadpole density (1 vs. 2 tadpoles/L) and high food variety (five food items vs. three food items) significantly increased tadpole body length and Gosner stage after 2 weeks (p < .001), increased survival to metamorphosis (p < .001), decreased time to metamorphosis (p < .001), and increased weight after metamorphosis (p < .001). On average, tadpoles in the high density/low food treatment, compared to the low density/high food, were 25% smaller after 2 weeks, had 3.9× lower survival to metamorphosis, took 1.25× longer to reach metamorphosis, and weighed 1.5× less after metamorphosis. In contrast, neither density (0.5 vs. 1 tadpole/L) nor mineral supplemented water affected growth and development, but tadpole survival was higher at 1 tadpole/L. Our findings demonstrate the feasibility of rearing boreal chorus frogs in captivity and provide guidelines for rearing this and similar species in a laboratory environment.

Ultrasound description of the coelomic cavity of the axolotl (Ambystoma mexicanum) in a clinically healthy population: a pilot study

Axolotls (Ambystoma mexicanum) are extensively studied for their relevance in human medical research. Despite being critically endangered in the wild, they have gained popularity as household pets. Although they have been kept in captivity for over a century, detailed descriptions of their coelomic organ anatomy remain limited. Also, this species exhibits significant variations compared to other amphibians. Ultrasound is a non-invasive and painless medical imaging technique, ideally suited for investigating internal organs or structures. This study focused on describing the ultrasound appearance of the axolotl coelomic cavity. It details the identification, localization and parenchymal description of major organs in 28 neotenic axolotls using ultrasound frequencies ranging from 7 to 15 MHz. The accuracy of the results was validated by comparing ultrasound findings with necropsy results from one male and one female axolotl. The heart, lung surface, liver and reproductive tracts were visualized. Measurements, along with confidence intervals, were calculated for the spleen, kidneys, testicles, gastric wall, gallbladder, and pylorus. Occasional detection of hyperechoic millimetric particles in the gallbladder or ascites was noted. However, visualization of the pancreas and bladder was not possible. This research outcomes involve the development of a comprehensive atlas comprising images obtained throughout the study. Additionally, the experiment established a reproducible and readily accessible protocol for conducting anatomy-morphological assessments in axolotl medicine. This protocol stands as a crucial preliminary stage before advancing to lesion identification.

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.

Captive breeding, embryonic and larval development of Ranitomeyavariabilis (Zimmermann & Zimmermann, 1988), (Anura, Dendrobatidae)

A solid basis to address the conservation challenges of amphibians requires an increased knowledge on their natural history and biology. Recent data on reproductive modes in amphibians suggest that they are much more complex and variable than previously thought but understudied. However, detailed information on the reproductive history is especially important to fill the current knowledge gaps. Following recent taxonomic changes in Ranitomeyavariabilis, information about captive-breeding management, image-based measurements of total length and surface area of the silhouette for individuals from embryonic to metamorphic development, and detailed larval staging for captive-bred specimens are provided from French Guiana. The development of R.variabilis from the stage eight (Gosner 1960) through metamorphosis took 79 to 91 days (n = 6) with a survival rate of 46%. The developmental stages largely matched those of the generalized staging system of Gosner (1960), with differences in the stages when labia and teeth differentiation and atrophy of the oral apparatus occurred. Compared with other studies the total length of R.variabilis tadpoles was greater at given stages than those of R.variabilis from a Peruvian population and those of the sister species, R.amazonica. Other studies concerning growth curves based on surface area data revealed that R.variabilis tadpoles at peak size were larger than those of R.amazonica, R.imitator, R.reticulata, R.sirensis, and R.vanzolinii, but smaller than R.benedicta. Our results represent the first embryonic and larval staging for R.variabilis, and detailed information is provided on their initial life phases. These data may facilitate the identification of R.variabilis tadpoles in the wild, as well helping to clarify the biogeographical distribution and taxonomic arrangement of the species. In addition, knowledge is added to the captive-breeding methodology for the species.

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.

Organization of the galaninergic neuronal system in the brain of the gecko Hemidactylus frenatus

Galanin (GAL) is a 29 amino acid peptide present in the central nervous system (CNS) as well as peripheral tissues in vertebrates. However, the brain distribution pattern of GAL is understudied in reptiles. The aim of this study was to determine the organization of galaninergic neuronal system in the brain of the gecko Hemidactylus frenatus, a tropical and sub-tropical lizard, using rabbit anti-galanin antibody. In the telencephalon, GAL-ir perikarya and fibres were found in the lateral septal nucleus, but only GAL-ir fibres were observed in the striatum, nucleus accumbens, anterior commissure, nucleus centralis amygdalae, dorsal and medial septal nuclei, nucleus of the diagonal band of Broca and in the optic chiasma. In the preoptic region, a cluster of GAL-ir cells and fibres was observed in the periventricular preoptic area and lateral preoptic area. GAL-ir perikarya and fibres were observed in hypothalamic areas such as the supraoptic nucleus, suprachiasmatic nucleus, paraventricular nucleus, periventricular nucleus of the hypothalamus, infundibular recess nucleus and in the median eminence, whereas GAL-ir fibres were present in the pars distalis of the pituitary gland. In the thalamus, GAL-ir fibres were observed in the dorsomedial, dorsolateral, and medial thalamic nuclei. GAL-ir fibres were also detected in mesencephalic areas such as the optic tectum, torus semicircularis, ventral tegmental area and substantia nigra, brain stem as well as the spinal cord. The organization of GAL-ir cells and fibres throughout the gecko brain suggests several neuroendocrine, neuromodulatory and behavioural functions for GAL in lizards. The study provides new insights into the evolutionarily conserved nature of GAL peptide in squamate reptiles and forms a valuable basis for future comparative studies.

Glucocorticoids in relation to behavior, morphology, and physiology as proxy indicators for the assessment of animal welfare. A systematic mapping review

Translating theoretical concepts of animal welfare into quantitative assessment protocols is an ongoing challenge. Glucocorticoids (GCs) are frequently used as physiological measure in welfare assessment. The interpretation of levels of GCs and especially their relation to welfare, however, is not as straightforward, questioning the informative power of GCs. The aim of this systematic mapping review was therefore to provide an overview of the relevant literature to identify global patterns in studies using GCs as proxy for the assessment of welfare of vertebrate species. Following a systematic protocol and a-priory inclusion criteria, 509 studies with 517 experiments were selected for data extraction. The outcome of the experiments was categorized based on whether the intervention significantly affected levels of GCs, and whether these effects were accompanied by changes in behavior, morphology and physiology. Additional information, such as animal species, type of intervention, experimental set up and sample type used for GC determination was extracted, as well. Given the broad scope and large variation in included experiments, meta-analyses were not performed, but outcomes are presented to encourage further, in-depth analyses of the data set. The interventions did not consistently lead to changes in GCs with respect to the original authors hypothesis. Changes in GCs were not consistently paralleled by changes in additional assessment parameter on behavior, morphology and physiology. The minority of experiment quantified GCs in less invasive sample matrices compared to blood. Interventions showed a large variability, and species such as fish were underrepresented, especially in the assessment of behavior. The inconclusive effects on GCs and additional assessment parameter urges for further validation of techniques and welfare proxies. Several conceptual and technical challenges need to be met to create standardized and robust welfare assessment protocols and to determine the role of GCs herein.

Strong restructuration of skin microbiota during captivity challenges ex-situ conservation of amphibians

In response to the current worldwide amphibian extinction crisis, conservation instances have encouraged the establishment of ex-situ collections for endangered species. The resulting assurance populations are managed under strict biosecure protocols, often involving artificial cycles of temperature and humidity to induce active and overwintering phases, which likely affect the bacterial symbionts living on the amphibian skin. However, the skin microbiota is an important first line of defense against pathogens that can cause amphibian declines, such as the chytrid Batrachochytrium dendrobatidis (Bd). Determining whether current husbandry practices for assurance populations might deplete amphibians from their symbionts is therefore essential to conservation success. Here, we characterize the effect of the transitions from the wild to captivity, and between aquatic and overwintering phases, on the skin microbiota of two newt species. While our results confirm differential selectivity of skin microbiota between species, they underscore that captivity and phase-shifts similarly affect their community structure. More specifically, the translocation ex-situ is associated with rapid impoverishment, decrease in alpha diversity and strong species turnover of bacterial communities. Shifts between active and overwintering phases also cause changes in the diversity and composition of the microbiota, and on the prevalence of Bd-inhibitory phylotypes. Altogether, our results suggest that current husbandry practices strongly restructure the amphibian skin microbiota. Although it remains to be determined whether these changes are reversible or have deleterious effects on their hosts, we discuss methods to limit microbial diversity loss ex-situ and emphasize the importance of integrating bacterial communities to applied amphibian conservation.

Resurrecting biodiversity: advanced assisted reproductive technologies and biobanking

Biodiversity is defined as the presence of a variety of living organisms on the Earth that is essential for human survival. However, anthropogenic activities are causing the sixth mass extinction, threatening even our own species. For many animals, dwindling numbers are becoming fragmented populations with low genetic diversity, threatening long-term species viability. With extinction rates 1000–10,000 times greater than natural, ex situ and in situ conservation programmes need additional support to save species. The indefinite storage of cryopreserved (−196°C) viable cells and tissues (cryobanking), followed by assisted or advanced assisted reproductive technology (ART: utilisation of oocytes and spermatozoa to generate offspring; aART: utilisation of somatic cell genetic material to generate offspring), may be the only hope for species’ long-term survival. As such, cryobanking should be considered a necessity for all future conservation strategies. Following cryopreservation, ART/aART can be used to reinstate lost genetics back into a population, resurrecting biodiversity. However, for this to be successful, species-specific protocol optimisation and increased knowledge of basic biology for many taxa are required. Current ART/aART is primarily focused on mammalian taxa; however, this needs to be extended to all, including to some of the most endangered species: amphibians. Gamete, reproductive tissue and somatic cell cryobanking can fill the gap between losing genetic diversity today and future technological developments. This review explores species prioritisation for cryobanking and the successes and challenges of cryopreservation and multiple ARTs/aARTs. We here discuss the value of cryobanking before more species are lost and the potential of advanced reproductive technologies not only to halt but also to reverse biodiversity loss.

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.

Bold Frogs or Shy Toads? How Did the COVID-19 Closure of Zoological Organisations Affect Amphibian Activity?

Simple Summary

The visitor effect describes how zoo animals respond to the presence of visitors to their enclosures in a positive, negative or neutral manner. The period of enforced closure of zoos due to the COVID-19 pandemic in March 2020 (and subsequent reopening later that year) allowed for the effect of visitor presence to be evaluated on several species of amphibian. Results have shown that amphibian visibility (i.e., likelihood to be on show in their enclosure) is potentially influenced by the presence of people, and therefore, enclosure layout, collection planning and amphibian husbandry should consider how to minimize any negative influences of the viewing public.

Abstract

Amphibians are an understudied group in the zoo-focussed literature. Whilst commonly housed in specialist exhibits and of real conservation value due to the global extinction crisis, amphibian welfare is not often investigated empirically in zoo settings. The limited research that is available suggests that enclosure design (structure, planting and naturalistic theming) has a positive impact on the time that amphibians will be on show to visitors. However, the categorisation of any “visitor effect” (i.e., influences of visitor presence on amphibian activity and time on display) is hard to find. The COVID-19 pandemic forced the closure of zoological organisations in the UK for several months from March 2020, with gradual re-openings from the summer into autumn and winter. This event provided a unique opportunity to study the effect of the lack of visitors, the presence of essential zoo staff only, the wider return of organisational staff, and then the return of visitors over a prolonged period. This project at WWT Slimbridge Wetlands Centre assessed the number of individuals of six species of amphibian—common toad (Bufo bufo), common frog (Rana temporaria), smooth newt (Lissotriton vulgaris), pool frog (Pelophylax lessonae), golden mantella (Mantella aurantiaca) and golden poison dart frog (Phyllobates terribilis)—visible to observers under different conditions. All amphibians were housed in a purpose-built indoor exhibit of individual enclosures and were recorded when visible (as a proportion of the total population of the enclosure) during closure, the return of extra centre staff and visitor periods. The results showed species-specific differences in visibility, with some species of amphibian being more likely to be on view when the presence of people at their enclosure was less likely or in smaller numbers. Such differences are likely related to the specific camouflage or anti-predation tactics in these focal species. Further study to quantify amphibian sensitivity to, and perception of, environmental change caused by public presence (e.g., light levels and sound) would be useful welfare-themed research extensions. Our results can help inform husbandry, collection planning and amphibian enclosure design to reduce any noticeable visitor effects, and provide a useful benchmark for further, more complex, welfare assessment measures.

A practical method for storage, preservation and transportation of anuran urine samples using filter paper for hormone analysis

Anurans (frogs and toads) expelled urine when handled and it could provide insights into their physiological status. However, storage, preservation and transportation are often challenging. The study aimed to standardize and validate a field method for short-term storage and preserve of anuran urine samples using Whatman filter papers. To examine the efficacy of storage conditions and type of papers, urinary based enzyme immunoassays were used to measure progesterone and testosterone hormone metabolites. High-Performance Liquid Chromatography was performed and revealed immunoreactive progesterone and testosterone metabolites in the urine samples. Urinary hormone metabolites concentration stored in filter paper at room temperature and control samples stored in -20°C for the same period were similar. Whatman grade 50 was found to be more suitable for storage of hormones than grade 3 paper for the experiments performed.•

A cheap and simple storage method for storage of anuran urine in field conditions using filter papers.

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Anuran urine could be preserved and transported under ambient conditions without significant changes and loss of hormones.

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This method would facilitate the endocrine monitoring of anurans in remote areas where limited logistics are available.