Salamander Populations Research Articles

A novel genetic strategy to enable rapid detection of rare non-native alleles

Established invasive species represent one of the most harmful and challenging threats to native biodiversity, necessitating methods for Early Detection and Rapid Response. Cryptic invasions are particularly challenging and often require expensive and time-consuming molecular surveys which limits their usefulness for management. We present a novel application of the Fluidigm SNP-Type Assay to identify rare non-native alleles that significantly reduces the cost and time to generate diagnostic results. We demonstrate the efficacy of this method using experimental Fluidigm pools (99% accuracy) and sequence data (96% accuracy). We apply our novel methodology to an endangered population of California tiger salamanders in Sonoma County where two individual non-native tiger salamander hybrids have previously been detected since 2008. We screened 5805 larvae in 387 sample-pools containing 15 larvae each. We did not detect any non-native hybrids in the population, a result that was verified with sequence data, though we strongly recommend additional years of sampling to confirm hybrid absence. Our success with a challenging, large-genome amphibian suggests this method may be applied to any system, and would be particularly useful when it is necessary for conservation practitioners to rapidly identify rare taxa or genes of interest.

Environmental Drivers of Local Demography and Size Plasticity in Fire Salamanders (Salamandra salamandra).

Conspecific amphibian populations may vary widely in local demography and average body size throughout their geographical range. The environmental drivers of variation may reflect geographical gradients or local habitat quality. Among fire salamander populations (Salamandra salamandra), local demography shows a limited range of variation because high concentrations of skin toxins reduce mortality from predation to a minimum, whereas average adult body size varies significantly over a wide range. This study on four neighboring populations inhabiting the catchments of low-order streams in the upper middle Rhine Valley (Koblenz, Germany) focuses on the identification of local environmental drivers of variation in age and body size. I collected 192 individuals at two localities per stream, measured snout-vent length, clipped a toe for posterior skeletochronological age determination, and released salamanders in situ again. Populations were similar in age distribution. Local habitat quality accounted for a significant proportion of demographic variability, mediated by the impact of landscape-induced mortality risk, including roads and agriculture. Still, the main effect of variation in habitat quality was on adult body size, the result of growth rates of aquatic larvae and terrestrial juveniles. Larvae exposed to non-lethal heavy metal contamination in streams developed into smaller juveniles and adults than clean-water larvae, providing evidence for carry-over effects from one stage to another. The generally small average adult size in the Rhine Valley populations compared to those in other parts of the distribution range indicates the action of a still unidentified environmental driver.

Evaluating Abiotic and Biotic Predictors of Coastal Giant Salamander (Dicamptodon tenebrosus) Populations in Fish-Bearing Headwaters of the Oregon Coast Range

Evaluating Abiotic and Biotic Predictors of Coastal Giant Salamander (Dicamptodon tenebrosus) Populations in Fish-Bearing Headwaters of the Oregon Coast Range

The Influence of Environmental Conditions and Coinfection by Blood-Feeding Parasites on Red Blood Cell Physiology of an Ectothermic Host.

AbstractVector-borne blood parasites cause myriad sublethal effects and can even be deadly to endotherms, but far less is known about their impacts on ectothermic hosts. Moreover, the pathologies documented in endotherms are generally linked to infection by blood parasites rather than by their vectors. Here, we measured hematocrit, hemoglobin, and relative proportions of immature red blood cells to evaluate the physiological effects of two blood-feeding parasites and coinfection on ectothermic hosts, differentiating among pathological responses, extrinsic factors, and natural variations. We investigated a population of wild eastern hellbender salamanders (Cryptobranchus alleganiensis), which harbor leeches (Placobdella appalachiensis) that transmit blood parasites (Trypanosoma spp.) to their hosts, often resulting in coinfection. We observed seasonal changes in host hematology corresponding to water temperature and demonstrated their ability to modulate hematological parameters in response to acute stress. We reveal seasonal relationships between parasite dynamics and host physiology, in which peak parasitemia occurred when hosts had seasonally high hematocrit and hemoglobin concentrations. We found that coinfected individuals expressed symptoms of anemia, including a regenerative response to depletion of their red blood cells. We also documented a more pronounced pathological response to leech vectors than to the trypanosomes they transmit. Our research underscores the complex interactions between host physiology, multiple parasites, and environmental factors and highlights the pathologies associated with the vector in coinfections. Given the contributions of climate change and disease in the rapid global decline of ectotherms such as amphibians, our study provides timely foundational insights into multiple factors that influence their red blood cell physiology.

A Review on Adaptive Responses of Salamanders to Climate Change

Extinction rates of salamanders are predicted to rise exponentially under rapidly changing environmental conditions. Due to a wide range of anthropogenic activities, the populations of salamanders are highly threatened. The previous published data indicate that salamanders have adapted various plastic responses to acclimatize to the changing environment. These plastic responses help them to buffer the adverse effects of changing environments and also allow them to adapt to new habitats. The objectives of this review paper are to explore the impact of changing climate on salamanders, to elucidate the diverse strategies they employ to mitigate these challenges, and to evaluate the limitations and evolutionary significance of these measures. Additionally, this study will endeavor to forecast whether these adaptive changes are sufficient to address the evolving climate conditions.

Long-Term Dynamics of a Cave Salamander Population in a Region under Changing Climate

Long-Term Dynamics of a Cave Salamander Population in a Region under Changing Climate

Screening the antimicrobial, cytotoxic and hemolytic effects of skin-parotoid gland secretions of 13 taxa from six species and one hybrid population of Anatolian endemic Lycian salamanders (Genus: Lyciasalamandra)

Background and purpose: The diverse bioactive content in the skin and parotoid glands of amphibians makes them unique and highly potential sources for pharmacological developments. The main aim of the study is to determine the total protein amounts, in vitro cytotoxicities, antimicrobial activities and hemolytic effects of skin-parotoid secretions of these endemic Lycian salamanders (Genus: Lyciasalamandra). Materials and methods: Lycian salamander specimens of 13 taxa from six species and one hybrid population are collected from southwestern Anatolia. Skin-parotoid secretions were obtained, clarified, supernatants snapfrozen then lyophilized. Total protein amounts were determined by BCA assay kit. The cytotoxicity was determined on eight different cell lines (one healthy and seven cancerous) using MTT assay. The antimicrobial activity was assesed using 11 different microorganisms (nine bacteria and two yeast) from six genus by MIC method. Hemolytic effects were measured on rabbit red blood cells. Results: Lycian salamanders’ skin-parotoid gland secretions showed variable cytotoxic effects on all cell lines with IC50 values from 5.41 ± 0.17 μg/ml to ineffective. MIC results of antimicrobial activity tests were also variable and from 3.9 μg/mL to non-effective. Studied skin-parotoid secretions have no hemolytic activities on rabbit red blood cells at concentrations of 0.5, 5 and 50 μg/mL. Conclusions: Skin-parotoid gland secretions of Anatolian endemic Lycian salamanders have sufficient and remarkable therapeutic potential to be candidate sources of natural and biologically active substances for novel drug discoveries.

The Role of Experience in the Visual and Non-Visual Prey Recognition of Fire Salamander Populations from Caves and Streams

The Role of Experience in the Visual and Non-Visual Prey Recognition of Fire Salamander Populations from Caves and Streams

Impacts of Wildfire Burn Severity on Plethodontid Salamander Populations of Great Smoky Mountains National Park

Impacts of Wildfire Burn Severity on Plethodontid Salamander Populations of Great Smoky Mountains National Park

Population-level effects of prescribed fires on terrestrial salamanders

Prescribed fires are widely used for oak (Quercus) regeneration in hardwood forests, but the reported effects on terrestrial salamanders are variable, with some authors describing little to no effect of prescribed fire on salamanders and others reporting negative results. Factors such as variable fire intensity, sampling methodology, and imperfect salamander detection, which vary by study, may influence the effects of prescribed fires on salamanders. We examined the response of red-backed (Plethodon cinereus) and zig-zag (Plethodon dorsalis) salamanders to prescribed fire in forests of the Midwest U.S., accounting for changes in salamander behavior and detection by accounting for capture probability, and considering the influence of local fire intensity. We also explored the effects of fire on environmental variables (leaf litter depth, soil moisture, soil temperature, and soil pH) to identify possible mechanisms driving fire’s influence on salamanders. From spring 2019 through fall 2022, a total of 4922 salamander captures were recorded, representing 1939 individually marked salamanders at six coverboard grids in southern Indiana. Occurrence of fire affected survival and temporary emigration of salamanders, likely indicating that salamanders retreated underground, on two of the four grids. Fire occurrence and intensity did not significantly affect environmental variables except for leaf litter depth, which was negatively affected. However, soil moisture had a stronger influence on salamander capture probability than leaf litter. Overall, effects of prescribed fires on salamander populations in this study were inconsistent. In contrast, environmental factors had strong impacts on salamanders, but themselves exhibited either no relationship or a short-term relationship to prescribed fire variables. Notably, large salamander populations may be better able to tolerate prescribed fires. Such populations will be important to support during prescribed fire management to protect the species, especially as the effects of repeated prescribed fires and compounding effects are unknown. Understanding the interplay between forest management practices and wildlife habitat features such as soil moisture and leaf litter will be critical to identifying best practices for supporting wildlife populations reliant on such features during prescribed fires.

Oral administration of GnRH via a cricket vehicle stimulates spermiation in tiger salamanders (Ambystoma tigrinum).

More than 50% of caudates are threatened with extinction and are in need of ex-situ breeding programs to support conservation efforts and species recovery. Unfortunately, many salamander populations under human care can experience reproductive failure, primarily due to missing environmental cues necessary for breeding. Assisted reproductive technologies (ARTs) are a useful suite of techniques for overcoming or bypassing these missing environmental cues to promote breeding. Exogenous hormones are used to stimulate natural breeding behaviors or gamete expression for in-vitro fertilization or biobanking and are typically administered intramuscularly in caudates. While effective, intramuscular injection is risky to perform in smaller-bodied animals, resulting in health and welfare risks. This research investigated the spermiation response to hormone administration through a non-invasive oral bioencapsulation route using the tiger salamander (Ambystoma tigrinum) as a model species. Male salamanders were randomly rotated six weeks apart through four treatments (n = 11 males/treatment) in which animals received a resolving dose of gonadotropin-releasing hormone (GnRH) as follows: (1) Prime-Only (0.0 μg/g); (2) Low (0.25 μg/g); (3) Medium (1.0 μg/g); and (4) High (2.0 μg/g). All males were given a GnRH priming dose (0.25 μg/g) 24 hours prior to the resolving dose. Exogenous hormone was delivered inside of a cricket (Gryllodes sigillatus) that was presented as a food item by tweezers. Sperm samples were collected at 1, 3, 6, 9, 12, and 24 hours after the resolving dose and analyzed for quantity and quality. For all treatments, sperm concentration was produced in an episodic pattern over time. The Prime-Only treatment had a lower (p < 0.05) percent of sperm exhibiting normal morphology compared to treatments utilizing a resolving dose of GnRH. Overall, oral administration of GnRH is a feasible route of inducing spermiation in salamanders, yielding sperm of sufficient quantity and quality for in-vitro fertilization and biobanking efforts.

Should landscape variation in population status be assessed with individual‐ or population‐level indicators?

AbstractMonitoring trends in wildlife populations is essential to effective management. Evaluating only a single metric can be cost‐effective; however, how a given metric responds to environmental variation may differ from other population‐ or individual‐level metrics. Consequently, conclusions about the effect of environmental variation on a species should consider the relationship between different metrics. We investigated how population‐level metrics (occupancy and relative abundance) and an individual‐level metric (body condition) responded to landscape variation in 3 semi‐aquatic salamander species. In the summer of 2015 and 2016, we conducted repeated count surveys at 71 streams on the Cumberland Plateau, Tennessee, USA, actively counting and measuring salamanders. We estimated occupancy and abundance of larval and post‐metamorphic animals using community‐occupancy and community‐N mixture models, respectively. We estimated body condition of the most observed life stage for each species using a standardized mass index. All models included the same set of covariates for comparison. Occupancy and abundance responses for each life stage‐by‐species combination were positively correlated for 4 of 6 combinations, with salamander abundance responding to a larger suite of covariates. Body condition was not linked to covariates in the same fashion as population‐level metrics, although consistency across species was detected for 1 covariate, watershed size. Our results indicate that inter‐specific and inter‐life stage variation in evaluated metrics is present within salamanders of this study system. Management for populations of salamanders in the region should consider monitoring multiple response metrics, to capture both population‐ and individual‐level responses, as these may not always be correlated.

Influence of Natural Gas Pipeline Right-of-Ways on Eastern Red-Backed Salamander Occurrence in the Northern Appalachians

Abstract Road and pipeline infrastructure development for natural gas extraction often results in forest fragmentation, which could negatively influence habitat quality for many amphibian species. We investigated occurrence dynamics of the eastern red-backed salamander Plethodon cinereus in relation to natural gas pipeline rights-of-way (ROWs) and forest structure characteristics in northern Pennsylvania, USA. We sampled 80 sites across two study areas by using coverboards, with each site containing sampling plots at the center of the ROW, the edge of the ROW, and 10 m and 30 m into the adjacent forest. We assessed the influence of ROW age, ROW width, distance from ROW, and five forest structure characteristics on plot occupancy probability. Eastern red-backed salamander occupancy probability decreased with ROW age and increased with distance from ROW. Our results indicate that eastern red-backed salamanders are negatively influenced by forest fragmentation for natural gas ROWs. Moreover, responses were time dependent, with occupancy probability declining with ROW age. Due to low detections, we were unable to analyze data for the other amphibians and reptiles encountered during the study. Our capture data indicate that ROWs could improve habitat quality for some snake species, but additional research is needed to better understand the influence of ROWs on reptile species. To reduce future forest fragmentation and impacts on eastern red-backed salamander populations, managers could consider placing pipelines along existing linear clearings and enhancing the habitat quality of ROWs for salamanders.

Divergent population responses following salamander mass mortalities and declines driven by the emerging pathogen Batrachochytrium salamandrivorans.

Understanding wildlife responses to novel threats is vital in counteracting biodiversity loss. The emerging pathogen Batrachochytrium salamandrivorans (Bsal) causes dramatic declines in European salamander populations, and is considered an imminent threat to global amphibian biodiversity. However, real-life disease outcomes remain largely uncharacterized. We performed a multidisciplinary assessment of the longer-term impacts of Bsal on highly susceptible fire salamander (Salamandra salamandra) populations, by comparing four of the earliest known outbreak sites to uninfected sites. Based on large-scale monitoring efforts, we found population persistence in strongly reduced abundances to over a decade after Bsal invasion, but also the extinction of an initially small-sized population. In turn, we found that host responses varied, and Bsal detection remained low, within surviving populations. Demographic analyses indicated an ongoing scarcity of large reproductive adults with potential for recruitment failure, while spatial comparisons indicated a population remnant persisting within aberrant habitat. Additionally, we detected no early signs of severe genetic deterioration, yet nor of increased host resistance. Beyond offering additional context to Bsal-driven salamander declines, results highlight how the impacts of emerging hypervirulent pathogens can be unpredictable and vary across different levels of biological complexity, and how limited pathogen detectability after population declines may complicate surveillance efforts.

Non-native earthworms increase the abundance and diet quality of a common woodland salamander in its northern range.

The online version contains supplementary material available at 10.1007/s10530-023-03168-3.

Forecasting the flooding dynamics of flatwoods salamander breeding wetlands under future climate change scenarios.

Ephemeral wetlands are globally important systems that are regulated by regular cycles of wetting and drying, which are primarily controlled by responses to relatively short-term weather events (e.g., precipitation and evapotranspiration). Climate change is predicted to have significant effects on many ephemeral wetland systems and the organisms that depend on them through altered filling or drying dates that impact hydroperiod. To examine the potential effects of climate change on pine flatwoods wetlands in the southeastern United States, we created statistical models describing wetland hydrologic regime using an approximately 8-year history of water level monitoring and a variety of climate data inputs. We then assessed how hydrology may change in the future by projecting models forward (2025-2100) under six future climate scenarios (three climate models each with two emission scenarios). We used the model results to assess future breeding conditions for the imperiled Reticulated Flatwoods Salamander (Ambystoma bishopi), which breeds in many of the study wetlands. We found that models generally fit the data well and had good predictability across both training and testing data. Across all models and climate scenarios, there was substantial variation in the predicted suitability for flatwoods salamander reproduction. However, wetlands with longer hydroperiods tended to have fewer model iterations that predicted at least five consecutive years of reproductive failure (an important metric for population persistence). Understanding potential future risk to flatwoods salamander populations can be used to guide conservation and management actions for this imperiled species.

Incorporating caudate species susceptibilities and climate change into models of Batrachochytrium salamandrivorans risk in the United States of America

Worldwide, amphibians are threatened by several factors including climate change and pathogens. One emerging fungal pathogen, Batrachochytrium salamandrivorans (Bsal) has caused die-offs of European salamander populations, representing a conservation concern for hotspots of salamander diversity in the United States of America (U.S.A). While Bsal has not been detected in the U.S.A., previous work has suggested high invasion potential. As species susceptibility to Bsal is temperature dependent, we expect climate change to impact Bsal risk, which has not been explored. Here, we used predicted changes in environmental conditions, species-specific susceptibility estimates, and novel approaches assessing introduction risks to estimate current and future Bsal invasion risk. To generate predictions, we used geospatial data representing introduction risks, species susceptibility, and climatic suitability. Across climatic scenarios, our models predicted greatest overall risk of Bsal emergence in the southeastern and northwestern U.S.A. Bsal climatic suitability was greatest in the northwest, whereas the greatest number of susceptible species was predicted in the southeast. Under future scenarios, we predicted that climatically suitable areas for Bsal will be reduced by 3–14 % under the most extreme climate model.

Habitat connectivity supports the local abundance of fire salamanders (Salamandra salamandra) but also the spread of Batrachochytrium salamandrivorans

ContextHabitat connectivity can stabilise animal populations by facilitating immigration and genetic exchange, but it increases the risk of infectious diseases being spread by hosts. Chytridiomycosis caused by Batrachochytrium salamandrivorans (Bsal) threatens European salamander diversity. The extent to which the connectivity of populations of fire salamanders (Salamandra salamandra) contributes to the spread of Bsal remains unclear.ObjectivesWe analysed the impact of habitat connectivity of fire salamanders on the spread of Bsal. Moreover, we show how local salamander abundance is associated with habitat connectivity over a five-year period.MethodsWe developed fire salamander habitat suitability models (HSMs) for the Eifel area (Germany), currently considered the core of the range of Bsal in Europe. Habitat models were used to calculate pairwise resistance between salamander occurrences to test whether Bsal presence and salamander abundance were associated with habitat connectivity.ResultsFire salamanders are widely distributed in the Eifel. Solid bedrock and topographic positioning were important predictors of stream suitability as breeding habitats, while deciduous forests and grassland cover determined overall fire salamander habitat suitability along with breeding habitat suitability. Bsal-positive salamander occurrences were better-connected than Bsal-negative or untested occurrences. Nevertheless, fire salamander larvae were more abundant in well-connected sites.ConclusionThe connection of salamander populations by suitable habitat seems to support local salamander abundance while facilitating the spread of Bsal. In situ conservation measures counteracting host species connectivity to interrupt Bsal transmission pathways must be implemented with caution, as they may weaken the demographic advantages of connectivity.

Habitat value of constructed breeding pools for the endangered Sonoma population of California tiger salamander

AbstractHabitat creation is a common element of efforts to recover populations threatened by altered habitat. Unfortunately, human‐created habitats do not necessarily support re‐establishment of target species. We investigated the value of constructed vernal pools as breeding habitat for the endangered Sonoma County population of California tiger salamanders (Ambystoma californiense) by conducting 19 years of larval surveys in 118 pools that were natural (n = 40), constructed (n = 70), or natural with substantial human alterations (human‐altered, n = 8). California tiger salamander larval densities in human‐altered and natural pools declined over the study period, while larval densities in constructed pools showed non‐negative trends. Larval declines in natural pools may be attributed to long‐term degradation of the surrounding terrestrial habitat. Mean larval densities over the course of the study were equivalent between constructed and natural pools, when corrected for pool morphometry. In contrast, human‐altered pools had lower larval densities. To assure consistent California tiger salamander breeding, pools needed to be ≥30 cm deep and 240 m2 in area, with deeper (50–70 cm) and larger (1,600–1,800 m2) pools providing increased larval productivity. Over the study, there was no evidence of decrease in the rate of colonization of new pools. We conclude that constructed pools can be important tools in the recovery of imperiled pool‐breeding amphibians if proper design elements for the target species are considered.

Pool Age and Local Habitat Are Associated with Effective Number of Breeders in Spotted Salamander Populations Colonizing Created Vernal Pools

Population genetics can reveal whether colonization of created habitats has been successful and inform future strategies for habitat creation. We used genetic analysis to investigate spotted salamander (Ambystoma maculatum) colonization of created vernal pools and explored the impact of habitat characteristics on the genetic diversity and connectivity of the pools. Our first objective was to examine genetic structure, differentiation, diversity, and potential for a founder effect. Our second objective was to determine if habitat characteristics were associated with effective number of breeders, relatedness, or genetic diversity. We sampled spotted salamander larvae in 31 created vernal pools (1–5 years old) in Monongahela National Forest (WV) in May and June 2015 and 2016. The youngest pools exhibited genetic differentiation, a founder effect, and low effective number of breeders. Effective number of breeders was positively associated with pool age, vegetation cover, pool diameter, and sample size. Vegetation cover was also negatively associated with relatedness. Genetic diversity did not have strong environmental predictors. Our results indicated the effective number of breeders increased and genetic differentiation decreased within 4–5 years of pool creation, a sign of rapid colonization and potential population establishment. Our research also showed that higher vegetative cover within the pool and larger pool diameters could impact habitat quality and should be incorporated into future pool creation.