Native Amphibian Species Research Articles

Effects of glyphosate based herbicide exposure in early developmental stages of Physalaemus gracilis

The impact of environmental pollutants has been a focus of investigation in recent years. Studies assessing the effects of these pollutants are essential for understanding the challenges faced by non-target species. Among the many substances used for agricultural purposes, the herbicide glyphosate is one of the most widely marketed in recent years. This broad-spectrum herbicide is commonly used to protect a variety of crops. In this study, we evaluated the effects of chronic glyphosate exposure on a native amphibian species, Physalaemus gracilis. Amphibians, which develop in aquatic environments, are highly sensitive to pesticides. Because of this, we investigated morphological, physiological, behavioral, and biochemical parameters in the early stages of development. The animals were exposed to environmentally relevant concentrations of a glyphosate-based herbicide (0, 100, 350, and 700 µg L⁻¹) during their first seven days of life. As a result, we observed impairments in anti-predatory behavior, reduced body mass index, and scaled mass index, malformations of the mouth and intestine, increased acetylcholinesterase activity, cardiotoxicity, and oxidative stress. These findings underscore the importance of studying native non-target species and highlight the need to evaluate the effects of environmentally relevant concentrations, as well as to review legislation regarding permissible levels of glyphosate in surface water and public water supplies.

The distribution, diversity and conservation of the Mexican herpetofauna among its biogeographic provinces

Mexico houses a substantial diversity of amphibians and reptiles, with a large number of endemics. We generated a checklist of Mexico’s herpetofauna and their distribution among its biogeographic regions and provinces. We found a total 435 species of amphibians (70.6% endemic to Mexico), and 964 species of reptiles (60.7% endemic to Mexico). The Transition Zone had the greatest herpetofaunal richness, housing 90.8% of the amphibian species and 71.1% of the reptile species that inhabit Mexico. Amphibian and reptile richness decreased from south to north, with the highest richness in the Sierra Madre del Sur, followed by the Trans-volcanic Belt and the Sierra Madre Oriental. According to the IUCN Red List, currently 28.4% of the native species of Mexican amphibians and reptiles are in a category of conservation concern. The Transition Zone, specifically the Sierra Madre del Sur, is of utmost importance due to the conservation status of its species, since this biogeographic province is home to a large number of endemic species. The Neotropical and Nearctic Regions both have around 13% of their species included in some category of conservation concern. The pairwise Jaccard distances among the biogeographic provinces for amphibians and reptiles are highly correlated suggesting parallel patterns of similarity between these two taxonomic groups. We found a positive correlation between Jaccard distances and the length of the shared border between provinces and a negative correlation between Jaccard distance and the distance between the geographic centroids of the provinces, suggesting that geographic proximity plays an important role in the similarity of herpetofauna among biogeographic provinces. The number of species in a province was not correlated with its area or longitude but showed a negative correlation with its latitude. Cluster analyses showed three main clusters of biogeographic provinces for both amphibians and reptiles, with subclusters reflecting geographic proximity and shared habitats. These results highlight the importance of considering geographic factors, such as geographic proximity and habitat similarities, in understanding the distribution and conservation of amphibians and reptiles in Mexico.

Phenological mismatches mitigate the ecological impact of a biological invader on amphibian communities.

Horizon scans have emerged as a valuable tool to anticipate the incoming invasive alien species (IAS) by judging species on their potential impacts. However, little research has been conducted on quantifying actual impacts and assessing causes of species-specific vulnerabilities to particular IAS due to persistent methodological challenges. The underlying interspecific mechanisms driving species-specific vulnerabilities therefore remain poorly understood, even though they can substantially improve the accuracy of risk assessments. Given that interspecific interactions underlying ecological impacts of IAS are often shaped by phenological synchrony, we tested the hypothesis that temporal mismatches in breeding phenology between native species and IAS can mitigate their ecological impacts. Focusing on the invasive American bullfrog (Lithobates catesbeianus), we combined an environmental DNA (eDNA) quantitative barcoding and metabarcoding survey in Belgium with a global meta-analysis, and integrated citizen-science data on breeding phenology. We examined whether the presence of native amphibian species was negatively related to the presence or abundance of invasive bullfrogs and whether this relationship was affected by their phenological mismatches. The field study revealed a significant negative effect of increasing bullfrog eDNA concentrations on native amphibian species richness and community structure. These observations were shaped by species-specific vulnerabilities to invasive bullfrogs, with late spring- and summer-breeding species being strongly affected, while winter-breeding species remained unaffected. This trend was confirmed by the global meta-analysis. A significant negative relationship was observed between phenological mismatch and the impact of bullfrogs. Specifically, native amphibian species with breeding phenology differing by 6 weeks or less from invasive bullfrogs were more likely to be absent in the presence of bullfrogs than species whose phenology differed by more than 6 weeks with that of bullfrogs. Taken together, we present a novel method based on the combination of aqueous eDNA quantitative barcoding and metabarcoding to quantify the ecological impacts of biological invaders at the community level. We show that phenological mismatches between native and invasive species can be a strong predictor of invasion impact regardless of ecological or methodological context. Therefore, we advocate for the integration of temporal alignment between native and IAS's phenologies into invasion impact frameworks.

An updated checklist of the amphibians and reptiles of Nayarit, Mexico with conservation status and comparison with adjoining States

Herein, we present an updated list of the species of amphibians and reptiles that inhabit Nayarit, Mexico. In the years since the publication of a previous list in 2016, threats to amphibians and reptiles in Nayarit have continued unabated and efforts to more fully catalogue the richness of Nayarit’s herpetofauna have continued. Nayarit harbours 162 native species of amphibians and reptiles, representing 35 families and 85 genera. These include 37 species of amphibians (35 anurans and two salamanders) and 125 species of reptiles (one crocodile, 44 lizards, 69 snakes and 11 turtles). Of the amphibian and reptile species in Nayarit, 102 are endemic to Mexico and two endemic to Nayarit. The ecoregion with the highest richness of amphibians and reptiles in Nayarit is the Trans-Mexican Volcanic Belt followed closely by the Sierra Madre Occidental and then the Sierra Madre del Sur, the Pacific Lowlands and the Nayarit Islands. Just 5.8% of the species of amphibians and reptiles in Nayarit is IUCN-listed as Vulnerable, Endangered or Critically Endangered, 11.1% are placed in a protected category by SEMARNAT and nearly a third are categorised as high risk by the Environmental Vulnerability Score. The herpetofauna of Nayarit overlaps the most with Jalisco (88.9%). One of the main conclusions of our updated list of the amphibian and reptile species of Nayarit is that our understanding of the full complement of species is not complete, especially the reptiles.

In situ works on ecotoxicology in amphibians: current state of the art

Amphibians play a fundamental role in the functioning of ecosystems, mainly in the nutrient cycle, energy flow, and pest control. This group has a massive population decline, with approximately 41% of all species at risk, highlighting pesticide pollution as one of the main threats to the loss of anuran biodiversity. This occurs since amphibians have an epidermis with high permeability and a biphasic life cycle, where they use both the aquatic and terrestrial environments, allowing exposure and making them susceptible to chemical agents released into the environment. This makes amphibians a model group in ecotoxicological studies. However, due to the greater control of experimental conditions, the vast majority of studies are carried out in the laboratory, thus maintaining a gap in knowledge about the effects of pesticides on amphibians in natural environments. Under natural conditions, where environmental variables are not controlled, experiments must relate all the dynamics of the interaction of substances existing in the environment, and their influences on organisms. To evaluate the studies already performed under natural conditions, a bibliographic survey was carried out through a search with the Web of Science and SCOPUS databases, considering articles published in the last twenty years, using the terms 'field experimentation' or 'in situ study', associated with 'tadpole' and 'agrochemical' or 'pesticide', using a descriptive methodology. Twenty-one abstracts were pre-selected, they were further evaluated and the methodologies were checked to ensure only the analysis of experiments conducted in the field conditions. Thus, ten works were selected for the construction of the review. The works selected used native amphibian species, considered generalists, present in the study region, and were carried out in environments intended for agricultural cultivation with control groups in preserved locations. In these works, different methodologies were used, such as intentional spraying of water bodies, quantification of pesticides in the study sites, and verification of changes caused by the environment on tadpoles. The main evaluations were based on the survival and morphological changes of the tadpoles and, in some cases, on cytological and biochemical assays.

Metals, pesticides, and emerging contaminants on water bodies from agricultural areas and the effects on a native amphibian

In the Paraná River lower basin, an important agro-productive area of Argentina, crop fields and cattle breeding activities are common and may affect water quality. So, the aim of this study was to analyze the impacts of cattle breeding and agricultural activities on a stream from Buenos Aires, through physicochemical parameters (metals, pesticides, and emerging contaminants) and ecotoxicological parameters with Rhinella arenarum larvae, a native amphibian species. Three sites were selected on an ordinary plain stream that goes through agricultural fields and a cattle breeding establishment (upstream –S1-, near –S2- and downstream –S3- the establishment). Physicochemical parameters were measured in situ (in water) and in laboratory (in water and sediment samples: metals, pesticides, ivermectin and oxytetracycline). A semi-static chronic toxicity bioassay (504 h) was performed with water samples, and neurotoxicity, oxidative stress and genotoxicity biomarkers were measured after acute exposure (96 h). According to the index, a degradation in the water quality was observed in all sites. Ivermectin (8.03 mg/kg) and oxytetracycline (1.9 mg/kg) were detected in sediment samples from S2. Pesticides were detected in all sites, mainly in water samples: S1 presented the highest variability (7 residues) and in S3 AMPA, glyphosate and acetochlor concentrations were higher (10.3, 22.4 and 23.8 μg/L). Also, all sites significantly produced lethality at chronic exposure. Lethality at 504h was 40% for S1, 56.66% for S2 and 93.33% for S3. At acute exposure, the oxidative stress biomarkers were altered on R. arenarum larvae exposed to all sites and the neurotoxicity biomarkers were altered on larvae exposed to S1 and S3. Water quality was severely degraded by the surrounding agricultural and cattle breeding activities, which may represent a threat to the ecosystems.

Ecotoxicological assessment of complex environmental matrices from the lower Paraná River basin

Sediments of aquatic ecosystems constitute the fate of most atmospheric and terrestrial pollutants. Since aquatic organisms, such as amphibians, interact with sediments, the presence of pollutants may affect their survival, growth and reproduction. So, the aim of this study was to evaluate, the sediment and water quality of five sites from the lower basin of the Paraná River (Buenos Aires, Argentina) with different anthropic impacts: Morejón stream (S1), de la Cruz stream upstream (S2) and downstream (S3), Arrecifes river (S4), tributary stream of Arrecifes river (S5). Physicochemical parameters were measured in situ (water) and in laboratory (water and sediment samples). Also, a screening of metals and pesticides was performed. Chronic (504 h) lethal toxicity bioassays were performed exposing Rhinella arenarum larvae to sediment and water samples. Oxidative stress (catalase, superoxide dismutase, glutathione S transferase, reduced glutathione and lipid peroxidation) and genotoxicity (micronuclei test) biomarkers were analyzed at acute (96 h) exposure. According to the calculated water quality index, S1 and S3 showed excellent quality, S2 good quality and, S4 and S5 poor quality. Dissolved oxygen was low in all sites (2.26–5.63 mg/L) and S5 had the highest organic matter content. Copper levels exceeded the limit for the protection of aquatic life in S2 and S4; arsenic levels exceeded its limit in S4; and selenium levels exceeded its limit in S4 and S5. Pesticides were mainly detected in water samples. Sediment from S5 showed higher sulfide and organic matter concentrations. At 504 h, no significant mortality was observed in the control group while S5 caused the greatest mortality (80%), followed by S2 (66.67%), S1 (63.33%), S3 (46.67%) and S4 (43.4%). All samples caused oxidative stress and lipid peroxidation, and samples from S4 also caused genotoxicity. The analysis of sediment and water samples was a suitable approach to assess the effects of water bodies on a native amphibian species.

Distribution and Genetic Diversity of the Amphibian Chytrid in Japan.

While research on frog chytrid fungus Batrachochytrium dendrobatidis (Bd), an infectious disease that threatens amphibian diversity, continues to advance worldwide, little progress has been made in Japan since around 2010. The reason for this is, which we pointed out in 2009, that the origin of frog chytrid fungus may be in the East Asian region, including Japan based on the Bd ITS-DNA variation, and as few cases of mass mortality caused by this fungus have been observed in wild amphibian populations in Japan, the interest of the Japanese government and the general public in Bd has waned. However, we believe that organizing the data obtained so far in Japan and distributing the status of frog chytrid fungus in Japan to the world will provide useful insight for future risk management of this pathogen. We collected more than 5500 swab samples from wild amphibians throughout Japan from 2009 to 2010. Then, we investigated the infection status using the Nested-PCR method. We sequenced the obtained DNA samples and constructed a maximum-parsimony (MP) tree to clarify the phylogenetic diversity of Bd. We detected Bd infection in 11 (nine native and two alien) amphibian species in Japan and obtained 44 haplotypes of Bd ITS-DNA. The MP tree showed a high diversity of Bd strains in Japan, suggesting that some strains belong to Bd-GPL and Bd-Brazil. Except for local populations of the Japanese giant salamanders Andrias japonicus in Honshu Island and the sword tail newts Cynops ensicauda in Okinawa Island, the Bd infection prevalence in native amphibian species was very low. The alien bullfrog Aquarana catesbeiana had high Bd infection rates in all areas where they were sampled. No Bd infection was detected in other native amphibians in the areas where giant salamanders, sword tail newts, and bullfrogs were collected, suggesting that many native amphibians are resistant to Bd infection. The sword tail newt of Okinawa Island had both the highest infectious incidence and greatest number of haplotypes. The giant salamanders also showed relatively high infection prevalence, but the infected strains were limited to those specific to this species. These two Caudata species are endemic to a limited area of Japan, and it was thought that they may have been refugia for Bd, which had been distributed in Japan Islands for a long time.

Mortality of wild amphibians and reptiles admitted to a Wildlife Rehabilitation Center in Northern Portugal (2009 – 2017)

The data from 78 native species of reptiles and amphibians admitted to the Wildlife Rehabilitation Center of Parque Biológico de Gaia (Portugal) from 2009 to 2017 were revised to determine the main causes of morbidity and mortality. These data include four different orders: order Squamata (51.3%), order Testudinata (12.8%), order Anura (12.8%), and order Caudata (2.6%). 92.3% of the considered admittances were adults arriving during spring (41%) and autumn (29.5%). The main causes of admission to Rehabilitation Center were animals debilitated (12.8%) and injured (66.7%). Trauma was the major cause of mortality (78.2%). Unknown origin was the main cause of traumatic (71.8%) and non-traumatic (9.0%) death, followed by captivity related lesions (6.4%). These animals are excellent bioindicators of the health of the ecosystem and enable the identification of the main threats affecting them, especially those of anthropogenic origin. Studies of mortality on wild reptiles and amphibians are important to understand which the main threats and how human activity is affecting these populations.

Interspecific sensitivity of European amphibians towards two pesticides and comparison to standard test species

BackgroundAlthough debates about the assessment of potential effects of pesticides on amphibians are ongoing, amphibians are not yet considered in the current EU environmental risk assessment of pesticides. Instead, the risk assessment of potential effects on aquatic amphibian life stages relies on use of data of surrogate species like the standard temperate fish species rainbow trout (Oncorhynchus mykiss). This assumption is mainly based on the comparison to amphibian species not native to Europe such as the aquatic African clawed frog (Xenopus laevis). It remains unclear whether these surrogate species cover semi-aquatic Central European amphibian sensitivities. Therefore, we assessed the acute sensitivity of aquatic stages of eight European amphibian species native in Germany (Bufo bufo, Bufotes viridis, Epidalea calamita, Hyla arborea, Pelobates fuscus, Pelophylax sp., Rana dalmatina, R. temporaria) towards commercial formulations of the fungicide folpet (Folpan® 500 SC, Adama) and the insecticide indoxacarb (Avaunt® EC, Cheminova). The determined acute sensitivities (median lethal concentration, LC50) were included in species sensitivity distributions and compared to experimentally determined LC50 values of X. laevis and literature values of O. mykiss.ResultsThe results showed that native amphibian sensitivities differed between the tested pesticides with a factor of 5 and 11. Depending on the pesticide, X. laevis was five and nine times more tolerant than the most sensitive native amphibian species. Comparing literature values of O. mykiss to the experimentally determined sensitivities of the native amphibian species showed that the O. mykiss sensitivity was in the same range as for the tested amphibians for the formulation Folpan® 500 SC. The comparison of sensitivities towards the formulation Avaunt® EC showed an eight times lower sensitivity of O. mykiss than the most sensitive amphibian species.ConclusionsA risk assessment using the 96-h LC50 values for fish covers the risk for the assessed aquatic stages of European amphibians after the application of the recommended uncertainty factor of 100 and thus may be adequate for lower tier risk assessment of the studied pesticides. If aquatic amphibian testing will be required for pesticide risk assessment nevertheless, acute tests with the model organism X. laevis and the application of an appropriate uncertainty factor might be a promising approach.

Morphological, behavioral and genotoxic effects of glyphosate and 2,4-D mixture in tadpoles of two native species of South American amphibians

Pesticide contamination is an important factor in the global decline of amphibians. The herbicides glyphosate and 2,4-D are the most applied worldwide. These herbicides are often found in surface waters close to agricultural areas. This study aims at evaluating the chronic effects caused by glyphosate + 2,4-D mixture in Boana faber and Leptodactylus latrans tadpoles. The combined solution of the glyphosate and 2,4-D, in 5 different concentrations, was applied for 168 h. Herbicide mixtures did not affect the survival of the exposed tadpoles but growth and swimming activity were altered; besides causing several damages in the mouth and intestine. The erythrocytes showed micronuclei and other nuclear abnormalities. There is an ecological risk in the exposure of tadpoles of B. faber and L. latrans from the mixture of glyphosate + 2,4-D. Therefore, the approach used in this study provides important information on how commonly used pesticides can affect non-target organisms.

Surveying for Batrachochytrium dendrobatidis and B. salamandrivorans in wild and captive amphibian populations in Estonia and Latvia.

The pathogenic chytrid fungi Batrachochytrium dendrobatidis (Bd) and B. salamandrivorans (Bsal) cause infections that have become primary drivers of amphibian biodiversity loss. While globally widespread, the distribution margins of Bd and Bsal have not been determined, and the presence of these pathogens has probably gone unnoticed in many areas, especially in northern Eurasia. To better understand the presence and distribution of both pathogens in the northern temperate and boreal forest biomes, 243 individuals were sampled from 8 native amphibian species across Estonia. Additionally, 68 amphibians were sampled from captive collections in Estonia and Latvia. Pathogen infection was assessed using metabarcoding of the ITS2 marker. No positive matches for Bsal infection were found. Bd was detected in 13 specimens, 3 of which were sampled at the Riga Zoo (with a prevalence of 5.2%) and 10 in natural environments in Estonia (3.3%). The infected wild individuals belonged to 6 amphibian species and were detected throughout the mainland of Estonia, but not on islands. Prevalence of infection with Bd ranged between 3.1 and 12.5% among native species. In addition, we found molecular evidence for a potentially new sister species to Bd in nature. Although outbreaks of chytridiomycosis have never been observed in Estonia, it cannot be excluded that the dynamics of local amphibian populations are affected by Bd infections. Therefore, further work, including capture-mark-recapture studies and long-term monitoring, are required to clarify the impact of Bd on amphibians in Northern Europe.

Predicting global climatic suitability for the four most invasive anuran species using ecological niche factor analysis

Invasive species have a massive impact on their environment and predicting geographical zones at risk of invasion is paramount to the control of further invasions. Invasive anurans are particularly detrimental to native amphibian species, other vertebrates, and even aquaculture through competition, predation, disease transmission, toxicity, or a combination of these. Four species have been designated as the worst anuran invaders worldwide: Duttaphrynus melanostictus, Rhinella marina, Lithobates catesbeianus and Xenopus laevis. In this study, we modelled global habitat suitability for all four species using ecological niche factor analysis (ENFA) to predict the most susceptible areas to invasion. Models showed suitable climatic conditions for all four species expanded beyond their current native and invasive ranges. Tropical, subtropical, and island biomes around the world were among the areas with the highest ENFA suitability for all four species. Further, marginality statistics indicate niche expansion in D. melanostictus, and generalism in the three other species. As only climatic variables were used in the modelling, these results show the ultimate distributions if all landscape conditions are met without significant barriers to invasion.

Development and validation of four environmental DNA assays for species of conservation concern in the South-Central United States

We describe the development and testing of qPCR assays to detect four species of amphibians and reptiles of conservation concern in the South Central United States through environmental DNA (eDNA) samples. The target species include the Ringed Salamander (Ambystoma annulatum), Three-toed Amphiuma (Amphiuma tridactylum), Crawfish Frog (Rana areolata), and Chicken Turtle (Deirochelys reticularia). A set of primers and probes amplifying a 64–72 bp target regions were designed for each species from DNA sequence data for either the mitochondrial Cytochrome Oxidase I or Cytochrome B gene. All assays were assessed for target specificity, with no evidence of amplification in closely related or sympatrically-distributed non-target species. In vitro tests indicate that all assays consistently detect focal species down to concentrations of 2 × 10− 9 pg/µL. We evaluated the utility of qPCR assays on the eDNA samples collected during field surveys across Eastern Oklahoma, focusing on counties with vouchered historical records for the target species. Although detection rates were low for field applications of the assays, positive detection of Ambystoma annulatum, Rana areolata, and Deirochelys reticularia, but not Amphiuma tridactylum, were recorded. These assays can provide a practical tool for a non-invasive, genetic monitoring program that allows for both rapid detection and tracking of native aquatic and semi-aquatic amphibian and reptile species of conservation concern.

Ecotoxicity assessment and bioconcentration of a highly brominated organophosphate ester flame retardant in two amphibian species

Restrictions on the production and use of some highly toxic and persistent flame retardants has resulted in the increased use of alternative phosphate flame retardants that are less-well characterized. The brominated organophosphate ester flame retardant, tris(tribromoneopentyl) phosphate (CAS 19186-97-1, molecular formula C15H24Br9O4P, molecular weight 1018.47 g/mol, acronym TTBrNP) is a compound with potential to bioaccumulate and disrupt endocrine functions. To determine the toxicity of TTBrNP, two Canadian native amphibian species, Lithobates sylvaticus and L. pipiens, were acutely (embryos and Gosner stage 25 (GS25) tadpoles) or sub-chronically (GS25-41 tadpoles) exposed to the following nominal concentrations of TTBrNP: 0 (water and solvent controls), 30.6, 61.3, 122.5 and 245.0 μg/L. Note, measured concentrations declined with time (i.e., 118%–30% of nominal). There was high survival for both species after acute and sub-chronic exposures, where 75%–100% survived the exposures, respectively. There were no differences in the occurrence of abnormalities or hatchling size between controls and TTBrNP treatments for either species exposed acutely as embryos or tadpoles. Furthermore, after 30 d of sub-chronic exposure of L. pipiens tadpoles to TTBrNP there were no effects on size, developmental stage, liver somatic index or sex ratio. Bioconcentration factors were low at 26 ± 3.1 L/kg ww in tadpoles from all treatments, suggesting biotransformation or limited bioavailability via aquatic exposures. Thus, using two species of anurans at different early larval stages, we found TTBrNP up to 245 μg/L to have no overt detrimental effects on survival or morphological responses that would suggest fitness-relevant consequences.

Herbicides employed in sugarcane plantations have lethal and sublethal effects to larval Boana pardalis (Amphibia, Hylidae).

The increasing demand for biofuels favored the expansion of sugarcane and, as a consequence, in the consumption of pesticides in Brazil. Amphibians are subject to pesticide exposure for occurring in or around sugarcane fields, and for breeding at the onset of the rainy season when pesticide consumption is common. We tested the hypothesis that herbicides used in sugarcane crops, although employed for weed control and manipulated at doses recommended by the manufacturers, can cause lethal and sublethal effects on amphibian larvae. Boana pardalis was exposed to glyphosate, ametryn, 2,4-D, metribuzin and acetochlor which account to up to 2/3 of the volume of herbicides employed in sugarcane production. High mortality was observed following prolonged exposure to ametryn (76%), acetochlor (68%) and glyphosate (15%); ametryn in addition significantly reduced activity rates and slowed developmental and growth rates. AChE activity was surprisingly stimulated by glyphosate, ametryn and 2,4-D, and GST activity by ametryn and acetochlor. Some of these sublethal effects, including the decrease in activity, growth and developmental rates, may have important consequences for individual performance for extending the larval period, and hence the risk of dessication, in the temporary and semi-permanent ponds where the species develops. Future studies should seek additional realism towards a risk analysis of the environmental contamination by herbicides through experiments manipulating not only active ingredients but also commercial formulations, as well as interactions among contaminants and other environmental stressors across the entire life cycle of native amphibian species.

A potential threat to amphibians in the European Natura 2000 network: Forecasting the distribution of the American bullfrog Lithobates catesbeianus

Freshwater biodiversity is declining at an accelerated pace. Climate change and associated global warming and changes in precipitation patterns, combined with the expansion of generalist -invasive species are two of the main threats. Niche-based models (NBMs) are becoming inevitable tools in invasive species risk assessment and in conservation decision-making. Lithobates catesbeianus is an invasive species globally known for its adverse ecological impacts on native amphibians and biodiversity. To assess species current and future climatic suitable areas at the global and European scales we used an ensemble forecasting approach. We considered six climatic variables, three timeframes (current, 2050, and 2070), and two CO2 emission scenarios. Temperature seasonality, minimum temperature of the coldest month, maximum temperature of the warmest month, and precipitation in the driest month were the most important variables predicting bullfrog occurrence. Globally currently 3.8% of land area is suitable for bullfrog and an increase of up to 5.2% in 2070 is expected. Increase in suitable areas is expected at higher latitudes, especially in North America and central Europe. Currently, 3.45% of total Natura 2000 area is suitable, and a predicted range gain of up to 355.93% (12.28%) is expected in the highest concentration scenarios predictions. This can indicate that the 64 native amphibian species present in the Natura 2000 network could be at increased risk. The choice of Natura 2000 for a geographic detailed analysis of the possible effects on native amphibians is due to its importance for habitats and wildlife conservation. Identification of its invasion-susceptible areas will allow resource and management practices optimization.

AMPHIBIAN MOVEMENT ACROSS A NEW RESIDENTIAL ROAD IN WESTERN WASHINGTON STATE

In this exploratory study, we investigated amphibian movement across a new 1.4-km residential road system adjacent to a wetland complex in Thurston County, Washington. We implemented this study prior to home construction, and before traffic levels associated with occupancy occurred. Our purpose was to document pond-breeding amphibian movement patterns to identify safe-crossing recommendations. One 24-h walking survey was conducted per month from October to December 2008, and in February 2009. We observed 7 native amphibian species and tallied 225 amphibian observations. The data showed differences in autumn to winter migration timing and direction relative to the wetland complex among species, sexes, and life stages. Most adults were moving toward the wetlands, whereas most juveniles were moving away. The highest number of observations occurred during the 00:00 to 03:59 h dark interval, corresponding with lowest local traffic volume. Nearly all observations for Northern Red-legged Frog (Rana aurora), Pacific Treefrog (Hyliola regilla), Long-toed Salamander (Ambystoma macrodactylum), and Northwestern Salamander (Ambystoma gracile) occurred after dark. However, Rough-skinned Newt (Taricha granulosa) peak movement occurred during daylight, corresponding with the highest traffic volume. We documented diffuse movement throughout the road system. Spatial analyses highlighted 2 significant crossing hot spots, including a 1.8-m diameter culvert. This study illustrates the importance of understanding the spatial and temporal patterns in pond-breeding amphibian migrations to effectively plan and implement measures to reduce amphibian road mortality. Prior to new development, we encourage proactive planning, such as connectivity, traffic, and traffic calming analyses to identify amphibian migration locations and reduce mortality. In areas with existing roads, such as the study site, we suggest implementation of mitigation measures paired with effectiveness monitoring.

Floodplains provide important amphibian habitat despite multiple ecological threats

AbstractFloodplain ponds and wetlands are productive and biodiverse ecosystems, yet they face multiple threats including altered hydrology, land use change, and non‐native species. Protecting and restoring important floodplain ecosystems requires understanding how organisms use these habitats and respond to altered environmental conditions. We developed Bayesian models to evaluate occupancy of six amphibian species across 103 off‐channel aquatic habitats in the Chehalis River floodplain, Washington State, USA. The basin has been altered by changes in land use, reduced river–wetland connections, and the establishment of non‐native American bullfrogs (Rana catesbeiana = Lithobates catesbeianus) and centrarchid fishes, all of which we hypothesized could influence native amphibian occupancy. Despite potential threats, the floodplain habitats had relatively high rates of native amphibian occupancy, particularly when compared to studies from non‐floodplain habitats within the species’ native ranges. The biggest challenge for native amphibians appears to be non‐native centrarchid fishes, which strongly reduced occupancy of two native amphibians: the northern red‐legged frog (Rana aurora) and the northwestern salamander (Ambystoma gracile). Emergent vegetative cover increased occupancy probability for all five native amphibian species, indicating that plant management may offer a strategy to counter the negative effect of centrarchids by providing refuge from predation. We found that temporary and permanent hydroperiod sites supported different species; hence, both should be conserved on the landscape. Lastly, human‐created and natural ponds had similar amphibian occupancy patterns, suggesting that pond construction offers a viable strategy for adding habitats to the floodplain landscape. Overall, floodplain ponds and wetlands provide important amphibian habitat, and we offer management strategies that will bolster amphibian occupancy in an altered floodplain landscape.

Disentangling effects of invasive species and habitat while accounting for observer error in a long‐term amphibian study

AbstractThe invasive American bullfrog (Lithobates catesbeianus) and a variety of non‐native sport fish commonly co‐occur in lowland lentic habitats of the western United States. Both invasive taxa are implicated in declines of native amphibians in this region, but few long‐term studies of communities exist. Further, field studies of invasive–native interactions are complicated by confounding habitat modifications and observation errors. We surveyed amphibians and measured habitat characteristics for 12 yr across 38 wetland sites within the Willamette Valley, Oregon, USA. We assessed the influence of invasive species, habitat, and their interactions on the distributions of five native amphibian species using a multispecies dynamic occupancy model that accounted for false‐negative and false‐positive detections. In general, habitat characteristics—such as within‐pond vegetation cover, surrounding forest, and drought severity—were important for local persistence of native species when bullfrogs co‐occurred. We also found evidence of a cumulative negative effect of bullfrogs and non‐native fish (families Centrarchidae and Ictaluridae) on northern red‐legged frog (Rana aurora) local persistence that was mediated by the dominance of invasive reed canarygrass (Phalaris arundinacea). Non‐native fish and bullfrogs had variable effects on native amphibian species, but neither invasive taxon appears to be causing declines in occupied sites within our study area. Moreover, species relationships with habitat differed when invaders were present, indicating that certain habitats may increase persistence of native amphibians in the invaded landscape.