Threatened Frog Species Research Articles

Assessing the breeding phenology of a threatened frog species using eDNA and automatic acoustic monitoring.

Climate change has driven shifts in breeding phenology of many amphibians, causing phenological mismatches (e.g., predator-prey interactions), and potentially population declines. Collecting data with high spatiotemporal sensitivity on hibernation emergence and breeding times can inform conservation best practices. However, monitoring the phenology of amphibians can be challenging because of their cryptic nature over much of their life cycle. Moreover, most salamanders and caecilians do not produce conspicuous breeding calls like frogs and toads do, presenting additional monitoring challenges. In this study, we designed and evaluated the performance of an environmental DNA (eDNA) droplet digital PCR (ddPCR) assay as a non-invasive tool to assess the breeding phenology of a Western Chorus Frog population (Pseudacris maculata mitotype) in Eastern Ontario and compared eDNA detection patterns to hourly automatic acoustic monitoring. For two eDNA samples with strong PCR inhibition, we tested three methods to diminish the effect of inhibitors: diluting eDNA samples, adding bovine serum albumin to PCR reactions, and purifying eDNA using a commercial clean-up kit. We recorded the first male calling when the focal marsh was still largely frozen. Chorus frog eDNA was detected on April 6th, 6 days after acoustic monitoring revealed this first calling male, but only 2 days after males attained higher chorus activity. eDNA signals were detected at more sampling locales within the marsh and eDNA concentrations increased as more males participated in the chorus, suggesting that eDNA may be a reasonable proxy for calling assemblage size. Internal positive control revealed strong inhibition in some samples, limiting detection probability and quantification accuracy in ddPCR. We found diluting samples was the most effective in reducing inhibition and improving eDNA quantification. Altogether, our results showed that eDNA ddPCR signals lagged behind male chorusing by a few days; thus, acoustic monitoring is preferable if the desire is to document the onset of male chorusing. However, eDNA may be an effective, non-invasive monitoring tool for amphibians that do not call and may provide a useful complement to automated acoustic recording. We found inhibition patterns were heterogeneous across time and space and we demonstrate that an internal positive control should always be included to assess inhibition for eDNA ddPCR signal interpretations.

Battling habitat loss: suitability of anthropogenic waterbodies for amphibians associated with naturally acidic, oligotrophic environments

Habitat destruction is a key threatening process for amphibians. Modified or anthropogenic waterbodies can be used to compensate for habitat loss, with several amphibian species utilising created or modified waterbodies. We measured usage of anthropogenic/modified waterbodies by adult and tadpole frog species, including threatened species, in coastal wallum habitat in eastern Australia. Nine road trenches/ditches, 8 artificial ‘lakes’, 6 golf course waterbodies and 13 natural waterbodies were surveyed for frog adults and tadpoles during the summer/spring period 2011–2012. Additionally, we examined the relationship between frog assemblages and environmental factors (water chemistry, aquatic predators, vegetation types), focusing on Litoria olongburensis and Litoria fallax. Frog species richness differed between waterbody types, with two of three threatened frog species present in both natural and anthropogenic/modified waterbodies. The frog assemblage was influenced by pH, turbidity, salinity and percentage cover of certain vegetation types. Measured abundance of L. olongburensis adults and tadpoles were highest in natural waterbodies with high sedge density and low pH. The measured abundance of adult L. fallax was highest within artificial lakes. We conclude that differences in water chemistry and vegetation density can affect the amphibian assemblage within these environments. Therefore, effective conservation of all frog species would be enhanced by conserving a variety of waterbody types. However, natural waterbodies are more likely to be used by threatened species and the conservation of these waterbodies provides the best conservation outcomes. Where habitat offsets may be required, environmental managers should critically assess the quality of constructed habitat for specialist frog species including those associated with acidic, oligotrophic environments.

Seasonal Activity Patterns of Golden Mantellas (Mantella aurantiaca)

The Golden Mantella (Mantella aurantiaca) is a highly threatened frog species found in east-central Madagascar. They are seasonally active and difficult to observe outside the summer breeding season. We used a captive population maintained within the native range of the species to examine two aspects of life history that otherwise would be impracticable to observe in the field: sheltering behavior and nearest neighbor distance (NND). We made weekly observations on seven groups of frogs for 1 yr, recording NND of each individual and how many individuals were sheltering under cover. We also recorded whether eggs were present in terraria to better define the breeding season and determine how time of year relates to NND and sheltering behavior. Frogs were closer together and more often took shelter during cool winter months. This corresponds to the time of year when fewer egg clutches were recorded. There was no difference between NND and sheltering behavior in wild-caught vs. captive-bred frogs, and there was no significant difference between NND of males and females. Golden Mantellas may be at increased risk from infectious diseases because behavior that increases contact between infected individuals can facilitate disease transmission.

Are local and traditional ecological knowledge suitable tools for informing the conservation of threatened amphibians in biodiversity hotspots?

Globally, amphibians are declining more rapidly than any other vertebrate group. A general shortage of funding for the support of focused scientific studies led us to investigate local and traditional ecological knowledge as an alternative data source for amphibian conservation. In this context, we undertook a questionnaire-based interview survey with forest-dwelling indigenous and non-indigenous communities across the Anamalai Hills, within the southern Western Ghats of India, to gather ecological knowledge on three cryptic and threatened frog species. Our results suggest that local communities possess ecological knowledge of frogs and that the magnitude of this knowledge is influenced by gender, community type, education, and age. Accuracy of local knowledge was primarily influenced by the morphological distinctiveness of the focal species, but cultural association and utilisation were also important factors especially for the enigmatic purple frog Nasikabatrachus sahyadrensis, which has uses in medicine and amulets.

Status and priority conservation actions for Australian frog species

Coherent, multi-species conservation strategies rely on up-to-date assessments of extinction risk, and prioritising and implementing well-founded management and research actions. Using IUCN criteria and methods, we reassessed the conservation status of all 243 Australian frog species. We also identified key threats and associated potential management actions. We subsequently scored the relative value, feasibility and current levels of implementation of all management and research actions for threatened and Data Deficient species. These scores were then used to rank the relative priority of management and research actions, identifying the highest priority actions for reducing extinction risk for Australia's frogs. Our revised assessment identified 45 threatened frog species in Australia, a 10% reduction from the 2004 assessment. However, the number of species assessed as Extinct increased by two, and four species were added to the Critically Endangered list. Improvements in conservation status for some species resulted from better knowledge and natural population stabilisation or recovery following disease impacts, rather than as a consequence of management. Improved knowledge has also resulted in a reduction of Data Deficient species from ten to eight. We found substantial reductions in species extinction risk may be achievable by implementing a relatively discrete set of well-targeted management and research actions. Given its simple and dynamic nature, our method can be regularly updated with new information, and can also be applied at different geographic scales. Our prioritisation will enable improved allocation of limited resources to maximise conservation outcomes for Australian frogs.

Predation by introduced cats Felis catus on Australian frogs: compilation of species records and estimation of numbers killed

Abstract ContextWe recently estimated the numbers of reptiles, birds and mammals killed by cats (Felis catus) in Australia, with these assessments providing further evidence that cats have significant impacts on Australian wildlife. No previous studies have estimated the numbers of frogs killed by cats in Australia and there is limited comparable information from elsewhere in the world. AimsWe sought to (1) estimate the numbers of frogs killed by cats in Australia and (2) compile a list of Australian frog species known to be killed by cats. MethodsFor feral cats, we estimated the number of frogs killed from information on their frequency of occurrence in 53 cat dietary studies (that examined stomach contents), the mean number of frogs in dietary samples that contained frogs, and the numbers of cats in Australia. We collated comparable information for take of frogs by pet cats, but the information base was far sparser. Key resultsFrogs were far more likely to be reported in studies that sampled cat stomachs than cat scats. The mean frequency of occurrence of frogs in cat stomachs was 1.5%. The estimated annual per capita consumption by feral cats in Australia’s natural environments is 44 frogs, and, hence, the annual total take is estimated at 92 million frogs. The estimated annual per capita consumption by pet cats is 0.26 frogs, for a total annual kill of one million frogs by pet cats. Thirty native frog species (13% of the Australian frog fauna) are known to be killed by cats: this tally does not include any of the 51 threatened frog species, but this may simply be because no cat dietary studies have occurred within the small ranges typical of threatened frog species. ConclusionsThe present study indicated that cats in Australia kill nearly 100 million frogs annually, but further research is required to understand the conservation significance of such predation rates. ImplicationsThe present study completed a set of reviews of the impacts of cats on Australian terrestrial vertebrates. Cat predation on Australian frogs is substantial, but is likely to be markedly less than that on Australian reptiles, birds and mammals.

Integrating bioacoustics, DNA barcoding and niche modeling for frog conservation – The threatened balloon frogs of Sri Lanka

Discovering and monitoring anuran populations that are in decline, and ascertaining boundaries for cryptic and rare species, is a challenge for their conservation management. Here, we integrate three techniques, bioacoustics (call), niche modeling and DNA barcoding as a test case to investigate how the combination of these methods can enhance search efficiency for previously unknown populations, especially for those species that are threatened. As a focal group, we considered a clade in the genus Uperodon earlier referred to as Ramanella, represented by four endemic species in Sri Lanka (U. nagaoi – Endangered; U. palmatus – Critically Endangered; U. obscurus – Vulnerable and U. rohani – possibly Least Concern); we focus on the two highly threatened species (U. nagaoi and U. palmatus). We used mitochondrial DNA barcodes (16S rRNA) to link species accurately to their call and subsequently predicted species distributions using MaxEnt-based niche modeling of known species locations and forest cover data to increase the efficiency of searching for new populations. Lastly, we analyzed call data for accurate and rapid identification of new and viable populations. Following enhanced predicted distribution models, we visited 14 potential sites and sampled for calls of the two highly threatened species. Within a period of two weeks of fieldwork, we discovered two new populations of U. nagaoi and one population of U. palmatus by identifying their calls in areas predicted by niche modeling; we also confirm species identities at several previously unconfirmed locations. Finally, we included the new locations to enhance the distributional predictions for the threatened species. We discuss our results in the context of integrating methods to facilitate conservation of rare and threatened frog species.

Frogs and Toads of Northern Belize

Belize is home to several threatened frog species. One of them, the Maya mountains frog, lives nowhere else in the world. This 4-page fact sheet written by Jenna M. Cole, Sarah K. Cooke, Venetia S. Briggs-Gonzalez, Justin R. Dalaba, and Frank J. Mazzotti and published by the UF/IFAS Wildlife Ecology and Conservation Department will help you identify your frogs and toads in order to better protect them.https://edis.ifas.ufl.edu/uw439

An extirpated lineage of a threatened frog species resurfaces in southern California

AbstractSouthern California has experienced widespread amphibian declines since the 1960s. One species, the Vulnerable California red-legged frogRana draytonii, is now considered to be extirpated from most of southern California. In February 2017 a population ofR. draytoniiwas discovered in the southern foothills of the San Bernardino Mountains of Riverside County, California, near the edge of the species’ historical distribution. This population belongs to an mtDNA lineage that was presumed to be extirpated within the USA but is still extant in Baja California, Mexico. This discovery increases the potential for future, evolutionarily informed translocations within the southern portion of this species’ range in California.

Variation in thermal niche of a declining river‐breeding frog: From counter‐gradient responses to population distribution patterns

Abstract When dams or climate change alter the thermal regimes of rivers, conditions can shift outside optimal ranges for aquatic poikilothermic vertebrates. Plasticity in thermal performance and preference, however, may allow temperature‐vulnerable fauna to persist under challenging conditions. To determine the effects of thermal regime on Rana boylii (Ranidae), a threatened frog species endemic to rivers of California and Oregon, we quantified tadpole thermal preferences and performance in relation to thermal conditions. We monitored temperature and censused populations across a coastal to inland cline in six catchments where dams have altered thermal environments in close proximity to river reaches with natural conditions. We found geographic variation in population distribution and abundance based on river size combined with water temperature. The large inland rivers that supported breeding frogs, although cooler in spring due to snowmelt, became warmer during the summer than occupied coastal sites. Inland populations were constrained to reaches where the average temperature over the warmest 30 days ranged from 17.6 to 24.2°C, higher than coastal rainfall‐driven systems where averages ranged from 15.7 to 22.0°C. Frogs in rivers with hypolimnetic‐release dams bred in colder waters than they did in free‐flowing rivers. Common‐garden and field translocation experiments revealed local adaptations in larval growth and phenotypically plastic thermoregulatory behaviour. Tadpoles from all rivers had a positive linear growth response to temperature, but individuals from inland rivers displayed intrinsically higher growth rates. Consistent with a counter‐gradient model of selection in which the response to temperature change is in the opposite direction of the change, individuals from cooler rivers selected warmer temperatures. When reared under common conditions, however, tadpoles showed similar temperature preferences regardless of source river. Our results suggest a role for local growth rate adaptation in structuring the distribution of Rana boylii. Plastic thermoregulatory behaviour by tadpoles may explain how small populations are able to persist where dams release cold water. Management of edgewater habitats to increase the availability of warm micro‐sites may ameliorate this impact.

Niche modeling for management-ready information in little-studied, threatened frog species assemblages

We use species distribution modeling to create easily testable hypotheses about the current and future distributions of Jamaican frogs, a little studied but highly endangered group. Our models simultaneously represent the best possible current estimate of the frogs’ ranges and provide clear guidelines for future survey work and habitat preservation efforts. We identify areas that contain the highest frog biodiversity, the highest per-unit area frog conservation benefit, and areas that are putative climatic refuges from outbreaks of the frog disease chytridiomycosis. In addition, we use the distribution models to create a set of easily falsifiable predictions about frog presence or absence. Testing these predictions using presence/absence surveys will provide management-ready information about model quality, population trajectories, changes in realized climate tolerance, and disease presence. We present a method of generating targeted conservation recommendations that will be applicable to many little-studied, cryptic taxa worldwide.

Growth and development of captiveGeocrinia rosea(Myobatrachidae): A rare species analogue

Using Geocrinia rosea as an analogue of the two threatened frog species, G. alba and G. vitellina, techniques were developed which contribute to an ex situ rearing program. We tested the effect of two levels of enclosure complexity on metamorph growth, and tested the effect of different substrate types on the success of egg clutch hatching and the subsequent development and growth of metamorph frogs. We found that the simplest enclosure was associated with the highest growth rates and better bone density of metamorphs, while a low pH sphagnum peat substrate was the better substrate for egg clutch survival and subsequent growth of metamorphs. Success of the program was highlighted by the rearing of second-generation frogs. These recommendations have now been applied to the captive management of the two endangered Geocrinia species.

Altitudinal records of data-deficient and threatened frog species from the Atlantic Rainforest of the Serra dos Órgãos mountains, in southeastern Brazil

Altitudinal records of data-deficient and threatened frog species from the Atlantic Rainforest of the Serra dos Órgãos mountains, in southeastern Brazil

Into the canyons: The phylogeography of the Malagasy frogs Mantella expectata and Scaphiophryne gottlebei in the arid Isalo Massif, and its significance for conservation (Amphibia: Mantellidae and Microhylidae)

Scaphiophryne gottlebei and Mantella expectata are two endemic and threatened frog species that live syntopically in the arid Isalo Massif in southern Madagascar. They share large parts of their distribution areas but differ in their natural history. Scaphiophryne gottlebei is more often found in canyons, while M. expectata prefers open habitats. Using samples from their known distribution areas, we investigated the genetic variability of these species by analyzing an approximately 600 base-pair fragment of the mitochondrial cytochrome b gene. Both species include a few widespread and common haplotypes as well as a number of other, geographically restricted ones. However, M. expectata exhibits more geographic substructure than S. gottlebei, in which one main haplotype represents individuals from various localities across the largest part of the distribution range. Comparing populations inside and outside of the Parc National de l’Isalo showed that the park does not harbour the bulk of the overall genetic diversity of the two species. These results emphasize the importance of so far unprotected habitats for the conservation of genetic variation in the endemic fauna of the Isalo region and of Madagascar in general.

Macroecology and extinction risk correlates of frogs

ABSTRACTAim Our aim was to test whether extinction risk of frog species could be predicted from their body size, fecundity or geographical range size. Because small geographical range size is a correlate of extinction risk in many taxa, we also tested hypotheses about correlates of range size in frogs.Location Global.Methods Using a large comparative data set (n = 527 species) compiled from the literature, we performed bivariate and multiple regressions through the origin of independent contrasts to test proposed macroecological patterns and correlates of extinction risk in frogs. We also created minimum adequate models to predict snout–vent length, clutch size, geographical range size and IUCN Red List status in frogs. Parallel non‐phylogenetic analyses were also conducted. We verified the results of the phylogenetic analyses using gridded data accounting for spatial autocorrelation.Results The most threatened frog species tend to have small geographical ranges, although the relationship between range and extinction risk is not linear. In addition, tropical frogs with small clutches have the smallest ranges. Clutch size was strongly positively correlated with geographical range size (r2 = 0.22) and body size (r2 = 0.28).Main conclusions Our results suggest that body size and fecundity only affect extinction risk indirectly through their effect on geographical range size. Thus, although large frogs with small clutches tend to be endangered, there is no comparative evidence that this relationship is direct. If correct, this inference has consequences for conservation strategy: it would be inefficient to allocate conservation resources on the basis of low fecundity or large body size; instead it would be better to protect areas that contain many frog species with small geographical ranges.

Soil disturbance in integrated logging operations and the potential impacts on a fossorial Australian frog

Forestry practices have been shown to impact on amphibian species to varying degrees. Burrowing amphibian species may be of less concern as they may be able to escape the direct impacts of a logging operation. The giant burrowing frog Heleioporus australiacus is a threatened frog species in south-eastern Australia. Logging is currently excluded from known habitat of this species. We examine aerial photographs to determine the extent of soil disturbance in 15 coupes in which integrated logging has occurred and 15 unlogged coupes. We then examine the extent of soil disturbance in a standard operation in a simple field experiment to assess the potential for a logging operation to affect H. australiacus . Approximately 65% of a coupe experiences medium to high levels of soil disturbance during an integrated logging operation. These disturbances appear to be at a level which would be disruptive to an individual H. australiacus occupying such sites. Alternate logging practices result in varying levels of disturbance and therefore are likely to have varying impacts on individuals. Active management of an area following a logging operation may improve the habitat for H. australiacus and other soil organisms.

Population monitoring of the vulnerable wallum sedge frog (Litoria olongburensis) in north-eastern New South Wales

The literature on the population ecology of Australian frogs provides relatively few accounts of population monitoring. This has hampered our ability to understand how frog populations respond to dynamic rainfall patterns and to determine the stability of populations of threatened frog species. We conducted biannual monitoring of the wallum sedge frog (Litoria olongburensis) along transects at 10 sites over a 4-year period (1996–2000). We recorded six environmental parameters to assess their influence on our population indices. Monitoring of transects indicated that populations were rarely stable and fluctuated from year to year. Counts of adults were negatively influenced by rain during the previous day but positively influenced by rain during the previous week. This suggests that timing of recent rainfall has a differing influence on habitat use by adult frogs. Counts of adults were also significantly influenced by site and census period. Numbers of juveniles were influenced by rain during the previous three months, which may suggest that successful recruitment depends on higher water levels in the sedge swamps. Counts of juveniles were also significantly influenced by census period. Our analysis reveals that, after controlling for the influence of rainfall, the number of adult frogs per census varied between 10 and 20 per transect. The number of juveniles varied between 5 and 15 per transect per census. We conclude that the wallum sedge frog across the geographic range of our sites was not in decline during our monitoring period. In light of our findings we provide a review on population monitoring of Australian frogs.

Skeletochronological assessment of age structure and population stability for two threatened frog species

Populations that fluctuate in size may become small at particular times and therefore be at risk of extinction. I used skeletochronology to examine the potential for fluctuations in population size in the threatened frog species Geocrinia alba and Geocrinia vitellina from southwestern Australia. The change in number of lines of arrested growth (LAG) in toe bones of recaptured frogs indicated that most individuals probably gain one LAG annually. Therefore, skeletochronology can be used for age determination. From a combination of skeletochronology and a mark–recapture study, both species appear to live for a maximum of six years. However, the majority of adult males only bred in a single year, which gave rise to a consistently dominant three‐year‐old age class. A drop in the number of two‐year‐old frogs and a large increase in the number of three‐year‐olds (up to 85%) from 1993 to 1994 in both species highlighted the potential for substantial fluctuations in population size. Widespread changes in abundance of between 25 and 50% may therefore be expected over periods as short as one or two years, due to variation in recruitment success.