Members of our team, colleagues and friends recently attended the 9th World Congress of Herpetology, 5-10th January, 2020, at the University of Otago, Dunedin, New Zealand. It was an excellent congress, and there was a large contingent of amphibian chytridiomycosis researchers there! Some photos and abstracts below.
Global impacts of chytridiomycosis on amphibians
Scheele B (1)
(1) The Australian National University
Amphibians are the most threatened vertebrate class, with approximately one third of all species at risk of extinction. Like other vertebrate classes, habitat loss and degradation are key threats to amphibians. However, on top of habitat loss, uniquely, many amphibian species are also threatened by infectious diseases, whose emergence has been facilitated by anthropogenic trade and the associated breakdown of dispersal barriers. The global spread of the fungal pathogens Batrachochytrium dendrobatidis and B. salamandrivorans, which cause the disease chytridiomycosis in amphibians, has been associated with widespread amphibian declines. Here we present a spatio-temporal assessment of the global impacts of amphibian chytridiomycosis. We estimate that chytridiomycosis has contributed to the decline of 501 amphibian species over the past half-century, including 90 presumed extinctions. The number of declining species increased rapidly during the 1970s and peaked in the 1980s. The effects of chytridiomycosis have been greatest in large-bodied, range-restricted anurans in wet climates. Chytridiomycosis has caused declines across a broad range of amphibian families, with declines clustered in the Americas and Australia, but also scattered across Europe and Africa. Encouragingly, 60 species have shown signs of recovery, with increases in abundance and distribution reported. However, chytridiomycosis continues to be an ongoing threat for 197 species. Both B. dendrobatidis and B. salamandrivorans remain absent from some regions with high amphibian biodiversity, and limiting ongoing spread is a conservation priority. Preventing further chytridiomycosis-driven amphibian declines is dependent on developing effective mitigation actions to conserve species at high risk of extinction.
Bioacoustics reveal the calling activity of an endangered frog (Philoria kundagungan) in response to climate.
Bolitho L (1), Newell D (1), Hines H (2)
(1) School of Environment Science and Engineering, Southern Cross University
(2) Ecological Assessment Unit, Queensland Parks and Wildlife Service
The Mountain frog, Philoria kundagungan, is an endangered species endemic to the upland rainforests of subtropical eastern Australia. This species is considered to be at risk from climate change however, population monitoring of P. kundagungan has been hampered by their cryptic calling behaviour and subterranean habits. The influence of environmental variables on calling activity was investigated at six sites across the species’ geographic and altitudinal range. Audio recording equipment (Wildlife Acoustics, Songmeter II) was deployed at each site and programmed to record sound once every hour for ten minutes, between July 2016 and March 2018. Soil temperature, along with a range of meteorological conditions were recorded every hour at each site. Kaleidoscope Pro 4 (Wildlife Acoustics, Inc.), was used to automatically detect P. kundagungan calls in the 8760 hours of sound recordings and our analysis detected >2 million P. kundagungan calls. The true positive rate for the presence of P. kundagungan calls in 5000 randomly selected recordings was >98%. The results of this study indicate that calling activity is driven primarily by soil temperature and time of day. This study will allow future targeted surveys of this cryptic species to be conducted under conditions that induce calling activity thus increasing detection probabilities.
Tolerance and resistance in defence against amphibian chytridiomycosis
Grogan L (1,2), McCallum H (1)
(1) Environmental Futures Research Institute, Griffith University
(2) School of Environment, Science and Engineering, Southern Cross University
Animal defences against infection involve two distinct but complementary mechanisms: tolerance and resistance. Tolerance measures the animal host’s ability to limit detrimental effects from a given infection, whereas resistance is the ability to limit the intensity of that infection. The study of host tolerance to infection is a burgeoning area in the field of animal disease ecology. Unlike resistance, tolerance does not affect pathogen fitness, and hence does not promote antagonistic counteradaptation. There is a vast range in amphibian responses to infection with the main fungal agent of the worst vertebrate disease, chytridiomycosis (Batrachochytrium dendrobatidis; Bd). Here, we quantify measures of tolerance and resistance across the amphibian chytridiomycosis literature, comparing species, life-stages and individual level variation. Infection tolerance is important for the dynamics and co-evolution of Bd infection within amphibian communities. Some frogs die from chytridiomycosis infection loads that others can tolerate without detrimental effects. Furthermore, some frogs harbour intense infections of > 8 million zoospore equivalents, consistent with the concept of superspreading. Tolerant amphibian life-stages such as tadpoles can harbour chytridiomycosis in their mouthparts but do not die from disease. Such tolerant tadpoles can then rescue a population despite high mortality of adults, or alternatively act as reservoirs for infection. Sympatric species, and tolerant superspreaders may also act as infection reservoirs, promoting pathogen persistence, maintaining high force of infection, and driving less tolerant hosts to extinction. Improving our understanding of infection tolerance and resistance promises powerful new strategies for understanding and mitigating infectious diseases.
When chytrid fungus invades: Integrating theory and data to understand disease-induced amphibian declines
Briggs C (1)
(1) University Of California, Santa Barbara
The emerging amphibian fungal pathogen Batrachochytrium dendrobatidis (Bd) has led to severe amphibian declines around the globe. One of the challenges when attempting to mitigate the effects of Bd on amphibian populations is that different amphibian populations can show drastically divergent outcomes following Bd invasion. These include an increase in amphibian population density, no discernible change in population density, a decrease in density, and even population-level extinction. Here we integrate extensive data from amphibian-Bd systems and epidemiological theory to build a framework for predicting when and why amphibian populations might show different population-level trajectories upon Bd invasion. This framework allows us to place seemingly disparate population-level responses following Bd invasion in terms of known disease ecology theory to better understand and manage amphibian declines and recoveries.
Evaluating environmental-DNA as a tool for detecting an amphibian pathogen using an optimized extraction method
Brannelly L (1), Wetzel D (2), Ohmer M (2), Zimmerman L (2), Saenz V (2), Richards-Zawacki C (2)
(1) University of Melbourne
(2) University of Pittsburgh
Environmental DNA (eDNA) detection is a valuable conservation tool because it can be used to detect and monitor imperiled species, invasive species, and wildlife pathogens within the environment. Batrachochytrium pathogens are of particular global conservation concern because they are a leading cause of amphibian decline. While there has been some research exploring the use of eDNA techniques to detect Batrachochytrium DNA in the environment, no single method appears to work in all situations. In this study, we first systematically compared eDNA extraction methods to find the most effective method for detecting Batrachochytrium dendrobatidis in water samples. Second, we used the extraction
method we found to be most effective on field-collected samples of both water and sediment. Using a quantitative PCR assay, we found that the most effective method for extracting Bd DNA from water filters was a soil extraction kit (Qiagen PowerSoil). We found that water filters were equivalent to amphibian skin swab samples for detecting the presence or pathogen DNA at the level of habitat, but that seasonal patterns of pathogen quantity were not equivalent between swabs and water samples. We also found that detection probability increased with the volume of water filtered. Overall, our detection of Bd eDNA presence was less sensitive for sediment samples. Our results indicate that eDNA samples, particularly filtered water samples, can be accurate in detecting pathogen presence at the habitat scale and could be an important conservation tool, however, eDNA’s utility in predicting infection risk and dynamics within a habitat is limited.
Mitigating chytrid fungus: successful translocation of a highly susceptible frog species to an environmental refuge
Hunter D (1), Scheele B (2), Gilbert D (7), Marantelli G (3), Gillespie G (4), West M (5), McFadden M (6)
(1) NSW Office Of Environment and Heritage
(2) Australian National University
(3) Amphibian Research Centre
(4) Department of Environment and Natural Resources Northern Territory Government
(5) The University of Melbourne
(6) Taronga Conservation Society Australia
(7) Zoos Victoria
Despite Batrachochytrium dendrobatidis (hereafter Bd) being a leading cause of frog declines globally, there are few examples of successful mitigation strategies to conserve susceptible species in the wild. We trialled the use of assisted colonisation to establish a population of the Spotted Tree Frog (Litoria spenceri), an endangered riverine species from south-eastern Australia that is experiencing ongoing declines associated with Bd. We hypothesised that streams with warmer micro-climates and fewer reservoir host species may provide an environmental refuge and allow Spotted Tree Frogs to coexist with Bd. We identified a potential release site outside the historic range of L. spenceri that was significantly warmer (more than double the number of hours above 28 degrees Celsius during Dec-April) and which supported no other riverine frogs. Starting in 2014, we released 400 frogs into the candidate site, and 200 frogs to a control site where the species recently was extirpated due to Bd. Post-release survivorship and breeding was vastly different between the two sites. The new site achieved high survivorship (> 0.8 annual survivorship) and subsequent recruitment, which has resulted in an overall increasing population. By contrast, the historic control site achieved very low survivorship (< 0.3), no observed recruitment, and as a result the population has declined to fewer than 10 individuals. While it is too early to claim we have established a long-term, self-sustaining population of L. spenceri, our study demonstrates the potential for assisted colonisation be used as a management tool to secure wild populations of Bd susceptible species.
Recovery efforts for the critically endangered Southern Corroboree Frog (Pseudophryne corroboree)
McFadden M (1), Hunter D (2), Gilbert D (3), Byrne P (4)
(1) Taronga Conservation Society Australia
(2) NSW Office of Environment and Heritage
(3) Zoos Victoria
(4) University of Wollongong
The Southern Corroboree Frog (Pseudophryne corroboree) is a small myobatrachid frog restricted to Kosciuszko National Park that has rapidly declined in recent decades largely due to disease, caused by infection with Batrachochytrium dendrobatidis. Population numbers are critically low with the species now only occurring at translocation sites. Immediate management objectives for this species include establishing robust insurance colonies, maintaining populations in the wild via translocation, and developing efficient captive breeding and translocation methods to increase the longer term capacity and resilience of the program. Captive breeding colonies have now been established at Taronga Zoo, Zoos Victoria and the Amphibian Research Centre. The captive population has a genetically-diverse founder base established from wild-collected eggs over many years. Despite initial difficulties, reliably high captive breeding results have been achieved in recent years permitting the use of offspring for reintroduction and research. Experimental translocations currently include the translocation of eggs into artificial and natural pools at wild sites, eggs into artificial habitats at sites with reduced threat of the disease and frogs into large enclosures within their range that restrict vectors for the chytrid fungus.
How to Find a Frog in Forest- can detection dogs be used for conservation?
Gilbert D (1), Magrath M (1), Harnett C (1), Cooper M (3), Edwards L (4), Byrne P (2)
(1) Zoos Victoria
(2) University of Wollongong
(3) Department of Environment, Land, Water and Planning
(4) Canidae Development
Amphibians (frogs, salamanders and caecilians) are declining more rapidly than any other vertebrate taxa with over one third of known species facing extinction. The causal factors for this decline are numerous, as are the conservation actions available to managers. One management option available to ensure against extinction and promote wild recovery is the establishment of ex situ conservation breeding programs. One priority goal for ex situ CBP is to establish a genetically healthy population, which is essential if wild recovery is a long-term objective. However, ex situ programs are often established when the population of the target species has already declined dramatically, making collection of sufficient material challenging. This is further complicated if the species is cryptic and found in complex habitat.
The use of novel techniques to assist with detection of individuals should be explored to maximise chances of genetic collection. One technique that is widely used for the detection of cryptic objects is scent trained detection dogs. However, their reliability will depend on various factors, including strength of scent, wind, habitat complexity, sex and individual dog behaviour. Here we test methodology and effectiveness of detection dogs trained to locate the highly cryptic Baw Baw frog (Philoria frosti), highlight challenges faced and recommend future uses for detection dogs in amphibian conservation management.
Variation of the skin bacterial community and Batrachochytrium dendrobatidis infection in the frog Philoria loveridgei
Familiar López M (1), Rebollar E (2), Harris R (3), Vredenburg V (4), Hero J (5)
(1) School Of Environment And Science, Griffith University
(2) Centre for Genomic Sciences
(3) Department of Biology, James Madison University
(4) Department of Biology, San Francisco State University
(5) School of Science and Engineering, University of the Sunshine Coast
Globally, amphibian population decline and extinction has largely been driven by chytridiomycosis (Batrachochytrium dendrobatidis- Bd). Amphibian skin bacteria are increasingly recognized as important symbiont communities with a relevant role in the defense against pathogens, inhibiting the growth of Bd. We aimed to describe the Bd infection status of wild populations of a terrestrial cryptic frog (Philoria loveridgei), and to determine whether infection status was correlated with changes in the skin microbial communities. Skin samples of P. loveridgei were collected along an altitudinal range in subtropical rainforests of southeast Australia. Sampling was conducted in two years during two breeding seasons with the first classified as a “La Niña” year. We used Taqman real-time PCR to determine Bd infection status and 16S amplicon sequencing techniques to describe the skin community structure. We found Bd positive frogs only in the second sampling year with low infection intensities, and no correlation between Bd infection status and altitude, frog sex or size. Skin bacterial diversity was significantly higher in P. loveridgei frogs sampled in the 1st year than in the 2nd year. In addition, 7.4% of the total OTUs were significantly more abundant in the 1st year compared to the 2nd year. We identified 67 bacterial OTUs with a significant positive correlation between infection intensity and an OTU’s relative abundance. Forty five percent of these OTUs belonged to the family Enterobacteriaceae. Overall, temporal variation was strongly associated with changes in Bd infection status and bacterial community structure of wild populations of P. loveridgei.
Differential outcome of chytridiomycosis within species: a review on influential variables
Sasso Lopes T (1), Grogan L (1), McCallum H (1)
(1) Griffith University
Since the identification of the infectious agent Batrachochytrium dendrobatidis (Bd) 20 years ago, numerous studies have helped to build solid documentation on the impact of chytridiomycosis worldwide. Bd presence in frogs has been investigated over a broad range of ecological scales. Studies have extended from differences in infection load within individuals, disease prevalence among populations, as well as presence of Bd across the landscape level. These studies examined both environmental and intrinsic species-specific factors to explain the variable occurrence of Bd within species in order to understand which processes underpin the disease dynamics and differential disease outcome. To evaluate the breadth of studies performed to date we quantitatively reviewed the Bd literature, and classified studies with regard to the spatial scale explored, methodological design and overall findings. We systematized which variables were most strongly associated with heterogeneity of disease occurrence. Among the 80 peer-reviewed papers published between 2004 and 2019 that fitted our criteria, air temperature and rainfall or humidity were commonly investigated environmental parameters. Variables such as life stage, distance to urban areas or zooplankton composition were seldom investigated, but were shown to influence Bd prevalence or infection load among different populations of the same species. Chytridiomycosis remains a dire threat to amphibians worldwide, and an intricacy of factors influences its occurrence and consequently its effects. Our review emphasises that understanding the complexity of Bd impact requires an integration of studies tackling Bd-host interaction at multiple scales and perspectives.
Frogs and fire: Can Australian frogs stand the flames?
Hollanders M (1), Grogan L (2), Newell D (1)
(1) School of Environment, Science, and Engineering, Southern Cross University
(2) Griffith Wildlife Disease Ecology Group, Environmental Futures Research Institute, Griffith University
Climate change is projected to increase the severity and frequency of wildfires globally and in Australia specifically. Understanding species response to wildfire is important for predicting fire impacts and identifying vulnerable taxa. The reponse of frogs to wildfire appears highly context-dependent, but is a globally understudied phenomenon. In this study, we quantitatively reviewed the literature on the effects of fire on Australian frogs. Nineteen studies were found, most of which only reported short-term effects and only 32% reported data from >5 years post-fire. Baseline data was often lacking with only 21% reporting pre-fire abundances. Less than a quarter of all studies reported a negative effect of fire on frog abundance, and more than a quarter reported a positive effect on frog abundance. The remainder of the studies found no effect or were unable to effectively analyse the data. Overall, many frog species appear resilient to fire, but more studies are needed to assess the species-level response to fire, including long-term studies.
First records of Batrachochytrium dendrobatidis in the endangered mountain frog (Philoria kundagungan) from eastern Australia
Bolitho L (1), Rowley J (2), Newell D (1)
(1) Southern Cross University
(2) Australian Museum
The amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd), has been implicated in the extinction of seven species in Australia to date. However, the full extent of its impact is still unknown due to data deficiency. In this study, we investigated the occurrence of Bd in the endangered Mountain Frog (Philoria kundagungan), a poorly known, range restricted species endemic to the headwater streams of cool temperate rainforests on the New South Wales and Queensland border in eastern Australia. We detected Bd via quantitative PCR on skin swabs from P. kundagungan across its full geographic range (an area of <300km2) including remote wilderness areas, rarely visited by humans. Overall infection prevalence was 47.3% of 75 individuals sampled, and 57.9% of 19 headwater streams sampled contained Bd infected individuals. Infection prevalence varied among headwater streams, but was not associated with elevation, snout-vent length, mass or sex of the examined frogs. Pathogen load ranged from 0 to 12435 zoospores, and mean infection intensity was highest in the south corresponding with higher rainfall and lower temperatures. Although no individuals were observed with clinical signs of chytridiomycosis, this was unsurprising given the typically short duration of clinical chytridiomycosis, and the cryptic nature of the species which necessitates detection via male advertisement calls. Hence, the impact of Bd on this species is still uncertain. As inhabitants of headwater streams, Mountain Frogs may act as a source of infection for amphibians downstream. Our results confirm that Bd is common in headwater streams even in highly protected and remote areas.
Prior pathogen exposure and a preliminary vaccine increase amphibian resistance to chytridiomycosis
Waddle A (1,2), Jaeger J (2)
(1) One Health Research Group, University of Melbourne
(2) School of Life Sciences, University of Nevada, Las Vegas
The amphibian disease chytridiomycosis, caused by Batrachochytrium dendrobatidis (Bd), presents a complicated challenge for captive breeding and headstarting programs that aim to introduce amphibians to sites where Bd is present. One possible solution for increasing the success of these efforts is to immunize animals before release. Immunizations against chytridiomycosis have been tested with limited enduring success in a few species, but the utility of vaccines to broadly mitigate chytridiomycosis in the wild is not known. For our experiments we used two species of ranids, the northern leopard frog (Rana pipiens) and the relict leopard frog (Rana onca), both of which have experienced drastic declines in the southwestern United States. For both species, the potential of successful reintroductions are likely limited by the presence of Bd. Therefore, we aimed to increase resistance of these species to chytridiomycosis using two approaches: (1) exposing frogs to a live Bd isolate that has previously demonstrated hypovirulence towards one of our study species; and (2) exposing frogs to a virulent Bd isolate followed by clearance with itraconazole. We found that both approaches led to drastically reduced Bd infections in previously exposed frogs as compared to naïve controls. Importantly, both approaches led to significantly greater survivorship. At this time our approach has not yet been field tested, but a proof-of-concept field experiment is currently being conducted to evaluate the potential importance of this conservation tool.
A simple viability assay for all life stages of the amphibian chytrid fungus, Batrachochytrium dendrobatidis
Webb R (1)
1) James Cook University
amphibian chytrid fungus, Batrachochytrium dendrobatidis, has caused widespread loss of biodiversity, impacting hundreds of amphibian species worldwide. It ranks as the world worst wildlife disease, but mitigation has been challenging as it is an unusual pathogen, requiring the development of new methods to enable experimental research. Despite its pathogenicity, B.dendrobatidis is a sensitive organism, and it is often necessary to perform viability estimates to confirm that cells are alive. Existing protocols to determine viability of B.dendrobatidis zoospores rely on the intact membranes of live cells excluding the dye. However the other life stage, zoosporangia, have porous walls. We instead assessed staining by methylene blue, which is rendered colourless by enzymes on live cells. We demonstrate that methylene blue (0.01mg/ml for 4 mins) can be used to quantify dead zoosporangia grown as adherent monolayers or in suspension using either microscopy or a colorimetric assay. Methylene blue can also be used to determine zoospore viability, allowing one protocol to be used for all life stages. Accurate quantification of B.dendrobatidis survival can aid amphibian conservation efforts by allowing rapid testing for susceptibility to antifungal drugs and other treatments.
Rapid differentiation of sexual signals in Cane toads Rhinella marina
Yasumiba K (1), Duffy R (2), Parsons S (2), Alford R (2), Schwarzkopf L (2)
(1) Tokyo University of Agriculture and Technology
(2) James Cook University
Advertisement calls tend to differ among populations, based on morphological and environmental factors, or simply geographic distance, in many taxa. Invasive cane toads (Rhinella marina) were introduced to Australia in 1935 and their distribution has expanded at increasing rates over time. Rapid evolution occurred in morphological and behavioural characters that accelerate dispersal, but the effects of rapid expansion on sexual signals have not been examined. We collected advertisement calls from four populations of different ages since invasion, and analysed the geographic differentiation of seven call parameters. Our comparisons indicate that the toad calls differ among Australian populations. The signal variation was not simply clinal with respect to population age, climate, or morphological differentiation. We suggest that selection on signalling among populations has been idiosyncratic and may reflect local female preferences or adaptation to environmental factors.
Using social media to benefit herpetology, your career, and public perception of reptiles and amphibians
Kolby J (1)
(1) James Cook University
The internet has become an extremely inexpensive, highly accessible, rapid tool to exercise science communication. In a way unlike ever before, multiple platforms stretching across Facebook, Instagram, Twitter and Tumblr provide us with an audience at our fingertips, reaching into the millions. Keeping in mind some basic strategies, we can use these platforms to share our love for herpetology, raise attention for our academic achievements, and build new relationships that can produce fruitful collaborations. I first approached social media with strong skepticism that it could help me as herpetologist, both academically and personally. Over the past 3 years, I’ve been amazed by the opportunities it has provided for me including producing videos for National Geographic, being interviewed multiple times about breaking news stories, and sparking a dramatic increase in the number of times my publications have been read and cited. In this presentation, I will help you unlock your potential and share what I’ve learned from my experiences diving into all of these social media platforms simultaneously. There are now many simple things that each of us can do online to help engage with the public and build a stronger global herpetological community.
Genomic approaches to amphibian conservation
Kosch T (1)
(1) Massey University
(2) University of Melbourne
Amphibians are the most threatened group of vertebrates with over one-third of species vulnerable to extinction. Two of the largest threats that amphibians face, emerging infectious diseases and climate change, do not currently have any long-term solutions leaving many species dependent on captive breeding and reintroduction programs for their continued survival. For such immitigable threats, facilitated evolution through genetic manipulation may be the only way to produce self-sustaining, resilient wild populations. Historically, genetic manipulation has been mostly restricted to model and agricultural species, but recent advances in genomic technologies and increased availability of reference genomes from resources such as the Vertebrate Genome Project make genetic manipulation for wildlife
conservation amendable for the first time. I will discuss how genetic manipulation can be applied to amphibian conservation to improve fitness in a changing landscape and some pros and cons of these approaches.
Associations between the fungal and bacterial microbiomes of frogs, with implications for disease management
McKnight D (1), Huerlimann R (1), Bower D (1,2), Schwarzkopf L (1), Alford R (1), Zenger K (1)
(1) James Cook University
(2) University of New England
Microbiomes play important roles in host health and ecology, but most research has focused on bacterial microbiomes, while largely ignoring fungal microbiomes. Therefore, we examined the fungal and bacterial microbiomes of four frog species following an outbreak of chytridiomycosis. Our goals were to compare the fungal and bacterial microbiomes, look for associations between them, and look for associations with Batrachochytrium dendrobatidis (Bd; the primary pathogen that causes chytridiomycosis). In total, we documented 1122 fungal operational taxonomic units (OTUs) and 765 bacterial OTUs; however, the mean number of OTUs per frog (richness) was lower for fungi than for bacteria. Additionally, bacterial communities tended to have low evenness and were similar among frogs within a species. In contrast, fungal communities generally had higher evenness and more variability among individuals. Despite these differences, there were positive correlations between the communities for both community structure and OTU richness, suggesting that either one community was driving the other or both were being affected similarly by other factors. We did not identify any associations between the structure of either community and Bd prevalence or infection intensity; however, both communities showed associations between OTU richness and Bd. For both communities, the most sensitive frog species (Litoria dayi) had the lowest richness. Further, there were negative correlations between OTU richness and Bd infection intensity, possibly suggesting a protective effect of richness. These results provide some of the first insights into the fungal microbiomes of wildlife and suggest that fungal microbiomes may have important roles in disease ecology.
World’s largest tropical island may provide refuge from the amphibian chytrid fungus Batrachochytrium dendrobatidis
Bower D (1), Jennings C (2), Webb R (3), Amepou Y (4), Schwarzkopf L (3), Berger L (5), Georges A (4), McKnight D (3), Alford R (3), Carr L (3), Clulow S (6)
(1) University Of New England
(2) Museum of Vertebrate Zoology, University of California
(3) James Cook University
(4) Institute for Applied Ecology
(5) Melbourne Veterinary School, University of Melbourne
(6) Department of Biological Sciences, Macquarie University
Emerging infectious diseases threaten the persistence of biodiversity globally. The amphibian chytrid fungus, Batrachochytrium dendrobatidis, is among the most widespread and damaging pathogen to biodiversity. New Guinea hosts 6% of the world’s frogs and is the largest landmass climatically suitable for Batrachochytrium dendrobatidis that may be free of the pathogen. We surveyed for Batrachochytrium dendrobatidis in Papua New Guinea, by swabbing live frogs in the Gulf Province and Eastern Highlands Province and by examining museum specimens from a range of sites and elevations. In total, all 442 samples were negative for Batrachochytrium dendrobatidis. The entry of Batrachochytrium dendrobatidis may have been prevented by the remoteness of Papua New Guinea and the unsuitable climate of its lowlands, which surround the climatically suitable highlands. Alternatively, Batrachochytrium dendrobatidis may be present in isolated patches but remain undetected, to date. We recommend a national disease surveillance program for chytrid fungi and crucial pre-emptive actions, designed to reduce the risk of pathogen transmission. Measures should include improved biosecurity protocols for trade and travel and continued disease surveillance in areas of probable entry and spread.
Impacts of the developmental environment on amphibian disease susceptibility
Ohmer M (1), Hall E (2), Brannelly L (3), Saenz V (1), Reinert L (2), Rollins-Smith L (2), Richards-Zawacki C (1)
(1) University Of Pittsburgh
(2) Vanderbilt University
(3) University of Melbourne
Changing environmental conditions may leave ectotherms with complex life cycles more vulnerable to disease via sublethal effects on physiology and immune function. In a rapidly changing climate, amphibian larvae are facing the dual threat of variable hydroperiods and increased water temperatures, and while developmental plasticity may allow some species to escape a drying pond, this plasticity might result in trade-offs with physiology and performance, including investment in immune function. Using two species of North American leopard frogs impacted by disease, we examined the effects of pond drying and elevated temperatures on development, growth, physiology, and immune function. Larvae were raised in mesocosms in Pennsylvania (Rana pipiens) and Louisiana (R. sphenocephala) under varying drying and heating regimes. We predicted that amphibians experiencing rapid pond drying and elevated pond temperatures would be smaller at metamorphosis and demonstrate lower survival and long-term alterations in physiology and immune function. In both Pennsylvania and Louisiana, rapid pond drying resulted in smaller metamorphic animals, but only R. sphenocephala in Louisiana responded to pond drying with an increase in developmental rate. Furthermore, drying and the impacts of drying (e.g. reduced size and a shortened larval period) resulted in reduced markers of innate and adaptive immune function in both species. Drying during development also reduced survival in R. pipiens after a pathogen challenge with Batrachochytrium dendrobatidis, but not in R. sphenocephala. Thus, a variable developmental environment can result in complex trade-offs between amphibian growth and immune function, which might increase the cost of pathogen resistance in some species.
Amphibian immunity, temperature, and disease: A balancing act between host and pathogen
Rollins-Smith L (1), Hall E (1), Reinert L (1), Miller B (2), Inman B (2), Richards-Zawacki C (3)
(1) Vanderbilt University School of Medicine
(2) Middle Tennessee State University
(3) University of Pittsburg
In an effort to understand the seasonality of skin defenses of Southern Leopard Frogs, Rana [Lithobates] sphenocephala, we examined their capacity to secrete antimicrobial peptides (AMPs) as we surveyed for the presence of the pathogenic chytrid fungi, Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans (Bsal). We found a predicted seasonality of Bd prevalence and intensity that was greatest in the cold seasons and the least in the summer and no evidence for the presence of Bsal. Because Southern Leopard Frogs are active for most of the year in Tennessee, we predicted that the capacity for an AMP defense would be constant throughout the year. Instead, we observed a distinct seasonality, with greater amounts of inducible peptides in fall, winter, and spring and the least available peptides in the summer. These findings suggest that this species may be adapted to produce and use more AMPs in the winter and spring during the most active breeding period when more frog-to-frog encounters would occur and skin defenses would be needed to deal with injuries. In summer, when adults are more solitary, such defenses might be of less importance, and other immune defenses might then be of greater importance for protection of the skin from potentially invasive skin pathogens.
The amphibian chytrid fungus in New Zealand
Bishop P (1), Eda A (1)
(1) University Of Otago
Chytrids were first detected in introduced frogs in 1999 in a pond in Christchurch. The presence of Bd was first detected in native frogs (Leiopelma archeyi) on the Coromandel Peninsula in 2001 and it was suggested that Bd was responsible for a mass decline (88%) in that population between 1994 and 2002. Although L. hochstetteri is the only endemic frog that breeds and lives in small high-altitude streams all sampling for Bd was negative, and in an experimental study, Bd was suggested to pose a low risk to leiopelmatids. Swabs taken from the other two species of native frogs, which only occur on islands, were negative, although positive Bd results have been obtained from all three introduced species of treefrog. An incursion of Alpine newts (Ichthyosaurus alpestris) was recently detected at the southern end of the Coromandel Peninsula and they were thought to have escaped from an illegal importer between 1995 - 2005. Many of these newts tested positive for Bd and it has been suggested that this is the original source of Bd in New Zealand. Populations of introduced frogs on South Island started to decline in the mid-2000s, and by 2008 large populations of R. raniformis in Central Otago disappeared. Over the last 10 years populations of introduced frogs have been recovering, and in recent studies these frogs are impossible to infect with laboratory strains of Bd. Current research is underway comparing skin microbiomes of Bd-exposed frogs to Bd-naïve frogs.
How does it end? Shifts in chytridiomycosis disease dynamics over time
Voyles J (1), Richards-Zawacki C (2)
(1) University Of Nevada, Reno
(2) University of Pittsburgh
Infectious diseases rarely end in extinction. Yet the mechanisms that explain how epidemics subside are difficult to pinpoint. We are characterizing host-pathogen interactions long after the emergence of a lethal fungal pathogen (Batrachochytrium dendrobatidis) in a tropical amphibian assemblage. In Panama, a subset of amphibian host species are recovering, but the pathogen is still present and is as pathogenic today as it was almost a decade ago. In addition, some amphibian species appear to be less susceptible than they were before disease emergence. Some evidence suggests that some hosts have defenses that are more effective now than they were prior to initial outbreaks. These results suggest that host recoveries cannot be attributed to pathogen attenuation and may be due to shifts in host responses and susceptibility. These findings provide insights into the mechanisms underlying disease transitions, which are increasingly important to understand in an era of emerging infectious diseases and unprecedented global pandemics.
Proactive Conservation: Developing strategies to combat the salamander-eating fungus
Bletz M (1), Nanjappa P (2), Woodhams D (1)
(1) University Of Massachusetts Boston
(2) Conservation Science Partners
Arrival of the fungus, Batrachochytrium salamandrivorans (Bsal), looms over the United States – a salamander diversity hotspot rivaled by no other around the world. This ‘salamander-eating’ fungus is decimating fire salamanders in Europe and poses immense threat to global salamander diversity. Therefore, understanding risk of Bsal invasion in the US and preparing for both how to respond if it emerges, as well as how to support population resilience through invasion, is essential. Three key strategies include prevention, management, and mitigation. Minimizing risk of pathogen entry through amphibian trade is critical; the 2016 USFWS listing of 201 salamanders as injurious under the Lacey Act was a first step in prevention. However, management of this pathogen will require additional regulatory measures, along with development of implementable science-based strategies to mitigate disease emergence and reduce spread. Disease response strategies in the wild can include altering water chemistry or temperature, modifying micropredator communities, applying fungicides, vaccination, and probiotic bioaugmentation. We characterized susceptibility across populations of eastern newts and two-lined salamanders, finding that populations differ in mucosal protection against Bsal. This crucial step identified geographic regions that are at greatest threat if Bsal invades, which in turn helps direct surveillance and management actions. Preliminary evidence from a controlled-laboratory experiment suggests that bacteria that produce volatile antifungal compounds (VOCs) may be able to limit infection buildup in hosts simply by being present in the environment. Continued development of integrative, multipronged approaches will be essential to combat significant biodiversity losses if Bsal emerges in the United States.
Optimising habitat management for amphibians: from simple models to complex decisions
Scroggie M (1), Heard G (1)
(1) Arthur Rylah Institute For Environmental Research, Victorian Department Of Environment, Land, Water and Planning
Habitat loss, degradation and fragmentation remain leading causes of amphibian declines across the globe. To mitigate these impacts, conservation managers may protect core habitats and pursue habitat creation or enhancement actions, including construction of artificial wetlands, manipulation of wetland hydroperiods, removal of invasive species or restoration of aquatic and riparian vegetation. Yet management budgets are universally tight. When planning such actions, managers face the fundamental and complex problem of choosing where and when to invest limited resources to maximise the likelihood of species persistence. Here, we extend our previous research on this problem, and demonstrate the utility of coupling occupancy models with optimisation algorithms to identify preferred habitat
management schemes across multiple, disjunct habitat networks. Our real-world case study, completed in close collaboration with conservation managers, focused on optimal habitat creation schemes for a threatened Australian frog in a rapidly urbanising region. Our new technique identified clear priorities for investment in wetland construction both among and within seven disjunct habitat networks, solving a spatial prioritisation problem that entailed millions of potential solutions and which was otherwise intractable. Such complex, multi-scale spatial prioritisation problems are pervasive in amphibian conservation. Coupling occupancy models with spatial optimisation algorithms represents a promising avenue to solve these problems and design habitat protection, creation and management schemes that maximise the chance of species persistence.
Understanding limits to recruitment can help inform chytrid fungus mitigation strategies.
West M (1,2), Todd C (3), Gillespie G (4), McCarthy M (1)
(1) University Of Melbourne
(2) National Environmental Science Programme, Threatened Species Recovery
(3) Arthur Rylah Institute
(4) Northern Territory Department of Environment and Resources
Understanding species’ differing population-level responses to threats can be key to identifying conservation options for declining populations. However, this is difficult when multiple threats are implicated. Chytrid fungus (Batrachochytrium dendrobatidis: Bd) is implicated in at least 500 amphibian population declines globally, although few tangible options exist to mitigate pathogen impacts. Other threatening processes including non-native predators, can contribute to amphibian declines and may exacerbate Bd impacts. We disentangled the impacts of Bd and non-native predatory fish upon two stream breeding frog species with differing conservation statuses to reveal vital rates that are crucial for species persistence. Litoria spenceri are threatened and historically occurred across a 300-1100m asl elevational gradient in south-eastern Australia. Litoria lesueurii are not threatened and sympatric with L. spenceri at some sites. Using mark-recapture derived demographic rates known to correlate with climate and elevation, discrete-time deterministic matrix population models were constructed for each species at high, moderate and low elevation sites, and under multiple management scenarios. Our study reveals that age to maturation, clutch size and egg-year 1 survival influenced interspecific and intraspecific population-level responses of the two frogs to Bd impacts. Importantly, our results highlight that a population’s capacity to counteract Bd-mediated adult mortality is clearly constrained by other threats and environmental interactions that limit species recruitment. Strategies to mitigate Bd impacts need to consider these interactions and constraints on recruitment.