Volunteer Conservation Action Data Reveals Large-Scale and Long-Term Negative Population Trends of a Widespread Amphibian, the Common Toad (Bufo bufo)

Potential hotspots of amphibian roadkill risk in Spain

We test a forecasting strategy to identify potential hotspots of amphibian roadkill, combining the spatial distribution of amphibians, their relative risk of collision with vehicles and data on road density in Spain. We extracted a large dataset from studies reporting road casualties of 39 European amphibian species and then estimated the 'relative roadkill risk' of species as the frequency of occurrence of casualties for each amphibian and standardized by the range of distribution of the species in Europe. Using a map with the spatial distribution of Spanish amphibians at a spatial resolution of 10 × 10 Km squares, we estimated the 'cumulative relative risk of roadkill' for each amphibian assemblage as the sum of risk estimates previously calculated for each species. We also calculated the total length of roads in each square (road density). Finally, combining all layers of information, we elaborated a forecasting map highlighting the potential amphibian roadkill risk across Spain. Our findings are relevant to suggest areas that should be focused on at more detailed spatial scales. Additionally, we found that the frequency of roadkill was unrelated to the evolutionary distinctiveness score and conservation status of amphibian species, while was positively correlated with their distribution range.

Efficacy of permanent wildlife fences as barriers to amphibian movement

To mitigate habitat fragmentation and roadkill, roads are increasingly equipped with wildlife fences and underpasses. However, the effectiveness of such fences in preventing road access for amphibians has not been tested under controlled conditions. In 2019 and 2020, we tested the efficacy of full panel fences of differing material, height, and shape (presence/absence of an overhang), to prevent road access for adult and juvenile amphibians. We selected five species according to locomotion mode: Natterjack toads (runners), European green toads (short-distance jumpers), agile frogs (proficient jumpers), American tree frogs (proficient climbers) and smooth newts (climbers). We found that Natterjack and green toads were unable to cross a concrete fence with a height of 13 and 24 cm, respectively. Addition of a 10 cm overhang reduced the height required to prevent crossing further to 10 and 17 cm, respectively. The ability of these less agile species to cross a certain fence height depended on body length. By contrast, jumping agile frogs and climbing tree frogs were not stopped by the greatest fence height tested (40 cm). However, addition of the overhang stopped the climbing tree frogs at a concrete fence height of 35 cm. An alternative metal fence (with overhang) was tested with some species and performed similar to the concrete fence (with overhang). Finally, the greatest concrete fence height passed by climbing juveniles was 20 cm (smooth newts). Hence, to stop amphibians from road crossing, we recommend the construction of durable (concrete or galvanized metal) and well-maintained fences with a minimum height of 40 cm with a 10 cm overhang.

Tracking wildlife diseases using community science: an example through toad myiasis

Parasite and pathogen surveillance is crucial for understanding trends in their distributions and host spectra, as well as to document changes in their population dynamics. Nevertheless, continuous surveillance is time-consuming, underfunded due to the non-charismatic nature of parasites/pathogens, and research infrastructure is usually limited to short-term surveillance efforts. Species observation data provided by the public can contribute to long-term surveillance of parasites using photographic evidence of infections shared on community science platforms. Here, we used public photo repositories to document the occurrence across space and time of Lucilia spp. (Diptera: Calliphoridae), a parasite inducing nasal toad myiasis in the European toad Bufo bufo (Anura: Bufonidae). We found a total of 262 toad myiasis observations on iNaturalist (n = 132), on GBIF (n = 86), on Flickr (n = 41), and on observation.org (n = 3). Our results indicate that the distribution of toad myiasis is regionally limited, despite its host being widely distributed and abundant across a wide region in Europe. Observations were found in 12 countries with relatively low prevalence, including Belgium (3.90%, CI 2.44–6.18), Denmark (1.26%, CI 0.89–1.80), France (0.45%, CI 0.14–1.38), Germany (1.27%, CI 0.92–1.75), Lithuania (0.50%, CI 0.13–1.98), Luxembourg (1.30%, CI 0.42–3.95), the Netherlands (2.71%, CI 1.61–4.52), Poland (0.89%, CI 0.34–2.35), Russia (Kaliningrad Oblast) (4.76%, CI 0.67–27.14), Switzerland (NA), Ukraine (0.87%, CI 0.12–5.91), and in the UK (0.45%, CI 0.28–0.72). Nevertheless, the number of uploaded observations of both parasite infection and host presence indicates a stable increase likely due to the growing popularity of community science websites. Overall, community science is a useful tool to detect and monitor certain wildlife diseases and to recognize potential changes in disease dynamics through time and space.

Bending the curve: Simple but massive conservation action leads to landscape-scale recovery of amphibians

The global decline of amphibians is part of the global freshwater biodiversity crisis. In human-dominated landscapes, amphibian population declines are driven by multiple stressors. A better understanding of the benefits of conservation action can contribute to the halting and reversal of population declines. Our analysis of 20 y of monitoring data shows that the large-scale construction of hundreds of new ponds in northern Switzerland has halted or even reversed declining trends for the majority of amphibian species, including multiple Red-Listed species undergoing declines at the national level. This conservation success suggests that increasing habitat availability benefits threatened amphibian species despite the continued presence of stressors known to negatively affect populations.

Success stories are rare in conservation science, hindered also by the research-implementation gap, where scientific insights rarely inform practice and practical implementation is rarely evaluated scientifically. Amphibian population declines, driven by multiple stressors, are emblematic of the freshwater biodiversity crisis. Habitat creation is a straightforward conservation action that has been shown to locally benefit amphibians, as well as other taxa, but does it benefit entire amphibian communities at large spatial scales? Here, we evaluate a landscape-scale pond-construction program by fitting dynamic occupancy models to 20 y of monitoring data for 12 pond-breeding amphibian species in the Swiss state Aargau, a densely populated area of the Swiss lowlands with intensive land use. After decades of population declines, the number of occupied ponds increased statewide for 10 out of 12 species, while one species remained stable and one species further declined between 1999 and 2019. Despite regional differences, in 77% of all 43 regional metapopulations, the colonization and subsequent occupation of new ponds stabilized (14%) or increased (63%) metapopulation size. Likely mechanisms include increased habitat availability, restoration of habitat dynamics, and increased connectivity between ponds. Colonization probabilities reflected species-specific preferences for characteristics of ponds and their surroundings, which provides evidence-based information for future pond construction targeting specific species. The relatively simple but landscape-scale and persistent conservation action of constructing hundreds of new ponds halted declines and stabilized or increased the state-wide population size of all but one species, despite ongoing pressures from other stressors in a human-dominated landscape.

Where Land and Water Meet: Making Amphibian Breeding Sites Attractive for Amphibians

The protection of wetlands is a cornerstone in the conservation of pond-breeding amphibians. Because protected wetlands are rarely natural areas, but are often man-made, at least in Europe, it is important that they are well managed to fulfill their intended function. Appropriate management requires knowledge of the ecology of the species, particularly habitat requirements. Here, we combine species monitoring data and habitat mapping data in an analysis where our goal was to describe the factors that determine the occupancy of amphibian species in federally protected amphibian breeding sites. As expected, every species had its own habitat requirements, often a combination of both a terrestrial and aquatic habitat (i.e., landscape complementation). In most species, occupancy was strongly positively affected with the amount of aquatic habitat, but predicted occupancy probabilities were low because the amount of aquatic habitat was low in most sites. The area or proportion of ruderal vegetation also had positive effects on multiple species, while other types of terrestrial habitat (e.g., meadows) led to low occupancy probabilities. The total area of the protected breeding sites was never included in a final model and connectivity was important only for one species (Triturus cristatus). The latter finding implies that the quality of the landscape between breeding sizes is more important than distance per se, while the former implies that the area of some specific habitats within breeding sites is crucial for high occupancies. Thus, increasing the amount of aquatic habitats and likewise terrestrial habitats within protected areas would make them more likely to achieve their conservation objectives. Our study is an example of how the joint analysis of monitoring data and habitat data (based on mapping in the field) can lead to evidence-based suggestions on how to improve conservation practice.

Gill Junction Injury and Microbial Disorders Induced by Microcystin-Leucine Arginine in Lithobates catesbeianus Tadpoles

Microcystin-LR (MC-LR) is widely present in waters around the world, but its potential toxic effects and mechanisms on amphibian gills remain unknown. In the present study, tadpoles (Lithobates catesbeianus) were exposed to environmentally realistic concentrations of 0.5, 2 μg/L MC-LR, and 0 μg/L MC-LR (Control) for 30 days with the objective to unveil the impairment of gill health. The lysozyme was downregulated, while pattern recognition receptors and complement and adaptive immune processes were upregulated and the ability of gill supernatant to inhibit pathogenic bacteria decreased in the 0.5 and 2 μg/L MC-LR groups. The transcriptions of epithelial barrier components (e.g., CLDN1) were significantly decreased in MC-LR-exposed gills, while the gill content of lipopolysaccharide (LPS) endotoxins and the transcriptions of downstream responsive genes (e.g., TLR4 and NF-κB) were concurrently increased. In addition, the number of eosinophils and the expression of pro-inflammatory cytokines (e.g., IL-1β and TNF-α) were increased. These results imply that exposure of tadpoles to low environmentally concentrations of MC-LR leads to inflammation, increased permeability, and a reduced ability to inhibit pathogenic bacteria. The epithelial cells of inner gill filaments increased and transcriptions of hypoxic stress genes (e.g., HIF-1α, FLT1, and SERPINE1) were upregulated within the exposed group. As a consequence, exposure to MC-LR may lead to hypoxic stress. MC-LR exposure also drove gill microbiota to a dysbiosis. The relative abundance of Elizabethkingia was positively correlated with content of LPS and transcriptions of NF-κB and TNF-α. Overall, this study presents the first evidence about the pronounced impacts of MC-LR exposure on gills of amphibians, highlighting the susceptibility of early developing tadpoles to the environmental risks of MC-LR.

Why link diverse citizen science surveys? Widespread arboreal habits of a terrestrial amphibian revealed by mammalian tree surveys in Britain

Terrestrial anurans, with their typically short limbs, heavy-set bodies and absent claws or toe pads are incongruous tree climbers, but even occasional arboreal locomotion could offer substantial advantages for evading predators or accessing new shelter or food resources. Despite recent interest, arboreal behaviour remains rarely and unsystematically described for terrestrial amphibians in Europe, likely due to fundamental differences in survey methods and therefore a lack of field data. However, other taxa surveys specifically target trees and tree cavities. We undertook collaborations and large-scale data searches with two major citizen science projects surveying for arboreal mammals in Britain to investigate potential tree climbing by amphibians at a national scale. Remarkably, we found widespread arboreal usage by amphibians in England and Wales, with occupancy of hazel dormouse (Muscardinus avellenarius) nest boxes, tree cavities investigated as potential bat roosts and even a bird nest, by common toads (Bufo bufo), but few additional records of frogs or newts. Of the 277–400 sites surveyed annually for dormice since 2009 at least 18 sites had amphibians recorded in nest boxes while of the 1388 trees surveyed for bats a total 1.4% (19 trees) had toads present. Common toads were found using cavities in seven tree species and especially goat willow (Salix caprea). Toads are potentially attracted to tree cavities and arboreal nests because they provide safe and damp microenvironments which can support an abundance of invertebrate prey but the importance of such tree microhabitats for toad conservation remains unknown and our results should be interpreted cautiously. We encourage expanding and linking of unrelated biodiversity monitoring surveys and citizen science initiatives as valuable tools for investigating ecological traits and interactions.

The genome sequence of the common toad, Bufo bufo (Linnaeus, 1758)

We present a genome assembly from an individual male Bufo bufo (the common toad; Chordata; Amphibia; Anura; Bufonidae). The genome sequence is 5.04 gigabases in span. The majority of the assembly (99.1%) is scaffolded into 11 chromosomal pseudomolecules. Gene annotation of this assembly by the NCBI Eukaryotic Genome Annotation Pipeline has identified 21,517 protein coding genes.

Estimation of breeding probability can make monitoring data more revealing: a case study of amphibians

Monitoring programs serve to detect trends in the distribution and abundance of species. To do so, monitoring programs often use static state variables. Dynamic state variables that describe population dynamics might be more valuable because they allow for a mechanistic understanding of the processes that lead to population trends. We fit multistate occupancy models to data from a country-wide multispecies amphibian occupancy monitoring program and estimated occupancy and breeding probabilities. If breeding probabilities are determinants of occupancy dynamics, then they may serve in monitoring programs as state variables that describe dynamic processes. The results showed that breeding probabilities were low and that a large proportion of the populations had to be considered to be non-breeding populations (i.e., populations where adults are present but no breeding occurs). For some species, the majority of populations were non-breeding populations. We found that non-breeding populations have lower persistence probabilities than populations where breeding occurs. Breeding probabilities may thus explain trends in occupancy but they might also explain other ecological phenomena, such as the success of invasive species, which had high breeding probabilities. Signs of breeding, i.e., the presence of eggs and larvae, were often hard to detect. Importantly, non-breeding populations also had low detection probabilities, perhaps because they had lower abundances. We suggest that monitoring programs should invest more in the detection of life history stages indicative of breeding, and also into the detection of non-breeding populations. We conclude that breeding probability should be used as a state variable in monitoring programs because it can lead to deeper insights into the processes driving occupancy dynamics.

Long-Term Monitoring of Amphibian Populations of a National Park in Northern Spain Reveals Negative Persisting Effects of Ranavirus, but Not Batrachochytrium dendrobatidis

Amphibians are the most highly threatened vertebrates, and emerging pathogens are a serious threat to their conservation. Amphibian chytrid fungi and the viruses of the Ranavirus genus are causing disease outbreaks worldwide, including in protected areas such as National Parks. However, we lack information about their effect over amphibian populations in the long-term, and sometimes these mortality episodes are considered as transient events without serious consequences over longer time-spans. Here, we relate the occurrence of both pathogens with the population trends of 24 amphibian populations at 15 sites across a national Park in northern Spain over a 14-year period. Just one out 24 populations presents a positive population trend being free of both pathogens, while seven populations exposed to one or two pathogens experienced strong declines during the study period. The rest of the study populations (16) remain stable, and these tend to be of species that are not susceptible to the pathogen present or are free of pathogens. Our study is consistent with infectious diseases playing an important role in dictating amphibian population trends and emphasizes the need to adopt measures to control these pathogens in nature. We highlight that sites housing species carrying Ranavirus seems to have experienced more severe population-level effects compared to those with the amphibian chytrid fungus, and that ranaviruses could be just as, or more important, other more high-profile amphibian emerging pathogens.

Emergence of a bufonid herpesvirus in a population of the common toad Bufo bufo in Germany

Bufonid herpesvirus 1 (BfHV1) was initially described in 2014 from cases of mortalities and dermatitis in Swiss populations of the common toad Bufo bufo. We identified a closely related herpesvirus strain in a German common toad population affected by an ongoing epidemic of multifocal proliferative to ulcerative skin disease since 2018.

Will predicted positive effects of climate change be enough to reverse declines of the regionally Endangered Natterjack toad in Ireland?

The global amphibian crisis is driven by a range of stressors including disease, habitat loss, and environmental contamination. The role of climate change remains poorly studied and is likely to influence environmental suitability, ranges, reproduction, and phenology. This study aimed to characterize the bioclimatic-habitat niche space of the Natterjack toad (Epidalea calamita) throughout its European range and to assess the impact of climate on the toad's environmental suitability and breeding behavior in Ireland, where declines in recent decades have resulted in it being regionally Red-Listed as Endangered. To address these questions, we first identified which climate variables best predict the current bioclimatic niche, fecundity (number of eggs deposit), and phenology. We then used future climate projections for two time periods (2041-2060 and 2061-2080) and two greenhouse gas emission scenarios (RCP 4.5 and RCP 8.5) to predict how the species range, fecundity, and phenology would change. The European range of the species was found to be limited by winter temperatures while its bioclimatic niche varied markedly throughout its range. Species distribution models suggested projected climate change will increase environmental suitability for the species throughout its range, including Ireland, but most notably in Scandinavia and the Baltic. Fecundity in Ireland was greatest during the cool temperatures of spring and after wet winters associated with ephemeral breeding pool availability. Warm, dry summers in the preceding year influenced fecundity the following spring indicative of carryover effects. Initiation of spawning was driven by spring temperatures, not rainfall. Projections suggested future climate change may increase fecundity in Ireland while spawning may commence earlier throughout the 21st century especially under a high greenhouse gas emission scenario (RCP 8.5). Despite recent range contraction and population declines due to habitat deterioration, the Natterjack toad, if subject to a suitable species conservation strategy, has the potential to be a climate change winner, notwithstanding unpredictable habitat and land-use change, sea-level rise inducing coastal erosion, changes in invertebrate prey abundance, and disease.

How citizen science could improve species distribution models and their independent assessment

Species distribution models (SDM) have been increasingly developed in recent years, but their validity is questioned. Their assessment can be improved by the use of independent data, but this can be difficult to obtain and prohibitive to collect. Standardized data from citizen science may be used to establish external evaluation datasets and to improve SDM validation and applicability.We used opportunistic presence-only data along with presence-absence data from a standardized citizen science program to establish and assess habitat suitability maps for 9 species of amphibian in western France. We assessed Generalized Additive and Random Forest Models' performance by (1) cross-validation using 30% of the opportunistic dataset used to calibrate the model or (2) external validation using different independent datasets derived from citizen science monitoring. We tested the effects of applying different combinations of filters to the citizen data and of complementing it with additional standardized fieldwork.Cross-validation with an internal evaluation dataset resulted in higher AUC (Area Under the receiver operating Curve) than external evaluation causing overestimation of model accuracy and did not select the same models; models integrating sampling effort performed better with external validation. AUC, specificity, and sensitivity of models calculated with different filtered external datasets differed for some species. However, for most species, complementary fieldwork was not necessary to obtain coherent results, as long as the citizen science data were strongly filtered.Since external validation methods using independent data are considered more robust, filtering data from citizen sciences may make a valuable contribution to the assessment of SDM. Limited complementary fieldwork with volunteer's participation to complete ecological gradients may also possibly enhance citizen involvement and lead to better use of SDM in decision processes for nature conservation.

Pesticide exposure affects reproductive capacity of common toads (Bufo bufo) in a viticultural landscape

Amphibian populations are declining worldwide at alarming rates. Among the large variety of contributing stressors, chemical pollutants like pesticides have been identified as a major factor for this decline. Besides direct effects on aquatic and terrestrial amphibian stages, sublethal effects like impairments in reproduction can affect a population. Therefore, we investigated the reproductive capacity of common toads (Bufo bufo) in the pesticide-intensive viticultural landscape of Palatinate in Southwest Germany along a pesticide gradient. In a semi-field study, we captured reproductively active common toad pairs of five breeding ponds with different pesticide contamination level and kept them in a net cage until spawning. Toads from more contaminated ponds showed an increased fecundity (more eggs) but decreased fertilization rates (fewer hatching tadpoles) as well as lower survival rates and reduced size in Gosner stage 25, suggesting that the higher exposed populations suffer from long-term reproductive impairments. In combination with acute toxicity effects, the detected sublethal effects, which are mostly not addressed in the ecological risk assessment of pesticides, pose a serious threat on amphibian populations in agricultural landscapes.

Small Hydropower Plants' Proliferation Would Negatively Affect Local Herpetofauna

Hydropower plants (HPPs) have a strong environmental impact on freshwater wetlands. Small diversion HPPs (SDHPPs) with 0.1–10 MW of installed power, redirect water from small mountainous rivers into several-kilometer-long tubes, disrupting complex dynamics of local aquatic food webs and their interactions with neighbor terrestrial food webs. It certainly affects local aquatic communities, but it is often neglected that two highly threatened vertebrate groups—amphibians and reptiles—which live in and around these wetlands, could be affected as well. In the Balkan peninsula, a part of Southeastern Europe, SDHPPs recently became very attractive and profitable for potential investors after they were proclaimed as eligible for subsidies from the national budget. As a result, in year 2020, the maximal projected number of SHPPs in the Balkans increased to 4,556. According to the literature data, ~28% of amphibian species in the Balkan Peninsula use small rivers and streams in the upper parts of watersheds as feeding, breeding and/or nursery habitats. Additionally, 38% of the total number of reptile species in Europe are registered in the hilly/mountainous areas of the peninsula, and 33% of these species strictly need humid habitats. The attempt of this mini-review is to present the facts which show that SHPPs and DSHPPs, in the way they are currently being installed, present harmful energy solution for the biodiversity of the mountain parts of Balkan peninsula, particularly for local amphibian and reptile populations which rely on lotic aquatic ecosystems and/or humid terrestrial habitats.

Combining spawn egg counts, individual photo-ID and genetic fingerprinting to estimate the population size and sex ratio of an endangered amphibian

According to the International Union for Conservation of Nature Red List, 41% of the world's amphibian species are threatened with extinction, making them more threatened than any other vertebrate group nowadays. Given the global amphibian crisis, comprehensive understanding of demographics and population trends of declining and threatened species is essential for effective management and conservation strategies. Counting egg spawns is widely used to assess population abundance in pond breeding anurans. However, it is unknown how such counts translate into robust population size estimations. We monitored the breeding activity of the Natterjack toad (Epidalea calamita), combining egg string counts and individual photo-identification with Capture-Mark-Recapture population size and operational sex ratio estimation. Male Natterjack toads were identified by the pattern of natural markings with repeated ID of the same individual confirmed for 10% of the samples using genetic fingerprinting. We identified 647 unique individuals within a closed study population at Caherdaniel, Co Kerry. Population estimates derived from egg string counts estimated a breeding population of 368 females (95% CI 353-384) and Capture-Mark-Recapture estimated a breeding population of 1698 males (95% CI 1000-2397). The female:male sex ratio was conservatively estimated at 1:5 (95% CI 1:3-1:6) where 62% ± 6% of females were assumed to spawn. These substantially departed from any priori assumption of 1:1 which could have underestimated the breeding population by up to 72%. Where amphibian absolute population size estimation is necessary, methods should include empirical survey data on operational sex ratios and not rely on assumptions or those derived from the literature which may be highly population and/or context-dependent.

Avoidance behavior of juvenile common toads (Bufo bufo) in response to surface contamination by different pesticides

Most agricultural soils are expected to be contaminated with agricultural chemicals. As the exposure to pesticides can have adverse effects on non-target organisms, avoiding contaminated areas would be advantageous on an individual level, but could lead to a chemical landscape fragmentation with disadvantages on the metapopulation level. We investigated the avoidance behavior of juvenile common toads (Bufo bufo) in response to seven pesticide formulations commonly used in German vineyards. We used test arenas filled with silica sand and oversprayed half of each with different pesticide formulations. We placed a toad in the middle of an arena, filmed its behavior over 24 hours, calculated the proportion of time a toad spent on the contaminated side and compared it to a random side choice. We found evidence for the avoidance of the folpet formulation Folpan® 500 SC, the metrafenone formulation Vivando® and the glyphosate formulation Taifun® forte at maximum recommended field rates for vine and a trend for avoidance of Wettable Sulphur Stulln (sulphur). No avoidance was observed when testing Folpan® 80 WDG (folpet), Funguran® progress (copper hydroxide), SpinTorTM (spinosad), or 10% of the maximum field rate of any formulation tested. In the choice-tests in which we observed an avoidance, toads also showed higher activity on the contaminated side of the arena. As video analysis with tracking software is not always feasible, we further tested the effect of reducing the sampling interval for manual data analyses. We showed that one data point every 15 or 60 minutes results in a risk of overlooking a weak avoidance behavior, but still allows to verify the absence/presence of an avoidance for six out of seven formulations. Our findings are important for an upcoming pesticide risk assessment for amphibians and could be a template for future standardized tests.

Potential pesticide exposure during the post-breeding migration of the common toad (Bufo bufo) in a vineyard dominated landscape

Two important drivers of the global amphibian decline are habitat destruction due to an intensification of farming and a related increase of pesticide applications. Recent studies have shown that there might be an underestimated risk of pesticides on terrestrial amphibians. However, there are too few data on the terrestrial habitat use of amphibians in agricultural landscapes to estimate the exposure risk. To fill this knowledge gap, we used telemetry to investigate the post-breeding migration of 51 common toads (Bufo bufo) from a breeding pond in a vineyard-dominated landscape in Southern Palatinate (Germany). We expected most toads to migrate to the nearby Palatinate Forest as a terrestrial habitat. However, only four individuals reached the forest, suggesting that a part of the population is inhabiting the agricultural landscape over large parts of the year. Individuals were also found directly in the vineyards (15% of all relocations), but 23% less often than expected from a random choice and therefore tend to avoid vineyards as terrestrial habitat. To estimate a possible spatial-temporal overlap of toad migration and pesticide application, we combined telemetry data with information about pesticide applications from local wine growers. Seven individuals had a high probability (>75%) of being directly exposed to a pesticide application. Taking spray drift and the half-life values of applied pesticides into account, the number of toads potentially exposed raised to 15 individuals. We estimated that, on a single day up to 24% of the whole breeding population came in contact with pesticides, resulting in a high overall exposure risk. Pesticides can have negative effects on amphibians, and toads try to avoid vineyards as habitats. Therefore, we conclude that a heterogeneous cultural landscape, with buffer strips around ponds, uncultivated patches and migration corridors, might be the best management measure for sustaining amphibians in the agricultural landscape.

Diets of European polecat Mustela putorius in Great Britain during fifty years of population recovery

Following nineteenth-century declines, polecats Mustela putorius are recolonising Great Britain. Polecat diet relates to two potential risks to recovery. First, rabbits Oryctolagus cuniculus, which are important prey for polecats, have experienced extreme population fluctuations, with near extirpation due to myxomatosis in the 1950s, recovery in 1960s–1990s and declines in 1990s–2010s. Second, polecats are secondarily exposed to anticoagulant rodenticides by eating contaminated rodents, and the frequency of polecat exposure to rodenticides is increasing. We analysed stomach contents from 99 polecats collected in 2012–2016 and compared results with earlier studies. Lagomorphs were the most abundant prey (66% frequency of occurrence, 95% confidence interval 53–74%), followed by other mammals (12%, 4–18%), amphibians (10%, 3–16%) and birds (7%, 1–13%). Diet varied seasonally; lagomorph occurrence was highest in spring and summer and lowest in autumn. Dietary niche breadth was greater in the 1960s, when rabbits were scarce, than in other decades, but did not differ between the 1990s and 2010s, indicating that diets have not diversified with recent rabbit declines. This may be because rabbit abundance is not yet low enough to cause dietary diversification or because polecats were collected in areas where rabbits were still abundant. Rodents did not increase in diet between the 1990s and 2010s and still occur with < 10% frequency, indicating that rodents need not contribute much to diet to expose polecats to rodenticides. This potentially limits the effectiveness of management actions designed to minimise polecat exposure to contaminated rodent prey.

Contribution of rare and common species to subterranean species richness patterns

AIM

Common species contribute more to species richness patterns (SRPs) than rare species in most studies. Our aim was to test this hypothesis using a novel model system, species living exclusively in subterranean habitats. They consist of mainly rare species (small ranges), only a few of them being common (large ranges), and challenge whether rare species are less important for the development of SRPs in this environment. We separately analyzed aquatic and terrestrial species.

LOCATION

Western Balkans in southeastern Europe.

METHODS

We assembled two datasets comprising 431 beetle and 145 amphipod species, representing the model groups of subterranean terrestrial and aquatic diversity, respectively. We assessed the importance of rare and common species using the stepwise reconstruction of SRPs and subsequent correlation analyses, corrected also for the cumulative information content of the subsets based on species prevalence. We applied generalized linear regression models to evaluate the importance of rare and common species in forming SRPs. Additionally, we analyzed the contribution of rare and common species in species-rich cells.

RESULTS

Patterns of subterranean aquatic and terrestrial species richness overlapped only weakly, with aquatic species having larger ranges than terrestrial ones. Our analyses supported higher importance of common species for forming overall SRPs in both beetles and amphipods. However, in stepwise analysis corrected for information content, results were ambiguous. Common species presented a higher proportion of species than rare species in species-rich cells.

MAIN CONCLUSION

We have shown that even in habitats with the domination of rare species, it is still common species that drive SRPs. This may be due to an even spatial distribution of rare species or spatial mismatch in hotspots of rare and common species. SRPs of aquatic and terrestrial subterranean organisms overlap very little, so the conservation approaches need to be habitat specific.

Continental-scale determinants of population trends in European amphibians and reptiles

The continuous decline of biodiversity is determined by the complex and joint effects of multiple environmental drivers. Still, a large part of past global change studies reporting and explaining biodiversity trends have focused on a single driver. Therefore, we are often unable to attribute biodiversity changes to different drivers, since a multivariable design is required to disentangle joint effects and interactions. In this work, we used a meta-regression within a Bayesian framework to analyze 843 time series of population abundance from 17 European amphibian and reptile species over the last 45 years. We investigated the relative effects of climate change, alien species, habitat availability, and habitat change in driving trends of population abundance over time, and evaluated how the importance of these factors differs across species. A large number of populations (54%) declined, but differences between species were strong, with some species showing positive trends. Populations declined more often in areas with a high number of alien species, and in areas where climate change has caused loss of suitability. Habitat features showed small variation over the last 25 years, with an average loss of suitable habitat of 0.1%/year per population. Still, a strong interaction between habitat availability and the richness of alien species indicated that the negative impact of alien species was particularly strong for populations living in landscapes with less suitable habitat. Furthermore, when excluding the two commonest species, habitat loss was the main correlate of negative population trends for the remaining species. By analyzing trends for multiple species across a broad spatial scale, we identify alien species, climate change, and habitat changes as the major drivers of European amphibian and reptile decline.

Effectiveness of small road tunnels and fences in reducing amphibian roadkill and barrier effects at retrofitted roads in Sweden

Schemes to reduce road impacts on amphibians have been implemented for decades in Europe, yet, several aspects on the effectiveness of such schemes remain poorly understood. Particularly in northern Europe, including Sweden, there is a lack of available information on road mitigation for amphibians, which is hampering implementation progress and cost-effectiveness analyses of mitigation options. Here, we present data derived from systematic counts of amphibians during spring migration at three previous hot-spots for amphibian roadkill in Sweden, where amphibian tunnels with guiding fences have been installed. We used the data in combination with a risk model to estimate the number of roadkills and successful crossings before vs. after mitigation and mitigated vs. adjacent non-mitigated road sections. In mitigated road sections, the estimated number of amphibians killed or at risk of being killed by car traffic decreased by 85-100% and the estimated number successfully crossing the road increased by 25-340%. Data, however, suggested fence-end effects that may moderate the reduction in roadkill. We discuss possible explanations for the observed differences between sites and construction types, and implications for amphibian conservation. We show how effectiveness estimates can be used for prioritizing amphibian passages along the existing road network. Finally, we emphasize the importance of careful monitoring of amphibian roadkill and successful crossings before and after amphibian passages are constructed.

Unexpected spatial population ecology of a widespread terrestrial salamander near its southern range edge

Under the current amphibian biodiversity crisis, common species provide an opportunity to measure population dynamics across a wide range of environmental conditions while examining the processes that determine abundance and structure geographical ranges. Studying species at their range limits also provides a window for understanding the dynamics expected in future environments under increasing climate change and human modification. We quantified patterns of seasonal activity, density and space use in the eastern red-backed salamander (Plethodon cinereus) near its southern range edge and compare the spatial ecology of this population to previous findings from the core of their range. This southern population shows the expected phenology of surface activity based on temperature limitations in warmer climates, yet maintains unexpectedly high densities and large home ranges during the active season. Our study suggests that ecological factors known to strongly affect amphibian populations (e.g. warm temperature and forest fragmentation) do not necessarily constrain this southern population. Our study highlights the utility of studying a common amphibian as a model system for investigating population processes in environments under strong selective pressure.

Fluctuations in population abundance in two anurans from Central Serbia

We monitored the population size of the agile frog (Ranadalmatina) and the common toad (Bufobufo) from 2011 or 2012, respectively, to the year 2017 at a syntopic breeding site in the vicinity of Belgrade. Adult R.dalmatina population size had minor fluctuations during the years of study (from 351 to 108 frogs). On the contrary, the adult B.bufo population was widely fluctuating towards decline (from 1158 to 141 toads). In both species, population fluctuations were not significantly related to variation of meteorological parameters (air temperature, humidity, precipitation). Density dependence effects on population size were not detected in either species. Apart from possible effects of climate change, the indicated trend towards decline of the monitored B.bufo population could also be the outcome of common population fluctuations or of increasing anthropogenic impact (vicinity of settlement and agricultural land). More years of monitoring more than one population are required to obtain precise information. Nevertheless, our results seem to be coherent with other studies that recommend conservation action for this species.

Urban environment and reservoir host species are associated with Batrachochytrium dendrobatidis infection prevalence in the common toad

Human-induced changes of the environment, including landscape alteration and habitat loss, may affect wildlife disease dynamics and have important ramifications for wildlife conservation. Amphibians are among the vertebrate taxa most threatened by anthropogenic habitat change. The emerging fungal pathogen Batrachochytrium dendrobatidis (Bd) has caused extinctions and population declines in hundreds of anuran species globally. We studied how the urban landscape is associated with the prevalence of Bd infections by sampling 655 anurans of 3 species (mainly the common toad Bufo bufo) in 42 ponds surrounded by different amounts of urban habitat (defined as towns, cities or villages). We also examined the association between Bd infections and a potential reservoir host species (the moor frog Rana arvalis). We found that 38% of the sites were positive for Bd with an infection prevalence of 4.4%. The extent of urban landscape was negatively correlated with Bd infection prevalence. However, the positive association of Bd with the presence of the possible reservoir species was substantially stronger than the urban effects. The body condition index of B. bufo was negatively associated with Bd infection. This Bd effect was stronger than the negative effect of urban landscape on body condition. Our results suggest that urban environments in Sweden have a negative impact on Bd infections, while the presence of the reservoir species has a positive impact on Bd prevalence. Our study also highlights the potential importance of Bd infection on host fitness, especially in rural landscapes.

Fatal phaeohyphomycosis due to Exophiala sp. infection in a free-living common toad Bufo bufo

A wild adult female common toad Bufo bufo found dead in Scotland in September 2016 was observed to have hepatomegaly, a large soft tissue mass in the coelomic cavity (2.7 g, 3.5 × 2.3 × 1.8 cm) and numerous dark-red papules (1-2 mm diameter) in the skin and subjacent tissue over the back and dorsal aspects of the limbs. Histopathological examination identified marked hepatitis and coelomitis associated with pigmented fungal hyphae, which are results consistent with a diagnosis of phaeohyphomycosis. Sequencing of the internal transcribed spacer region and the D1-D2 region of the large subunit of the ribosomal RNA gene from affected liver tissue identified the presence of Exophiala (Chaetothyriales) sp., a black yeast previously identified as a cause of amphibian phaeohyphomycosis. To our knowledge, this is the first published report of Exophiala sp. in a wild or captive amphibian in Europe and the first description of phaeohyphomycosis affecting a free-living amphibian in Great Britain. Exophiala spp. are saprobes and opportunistic pathogens. It has been postulated that phaeohyphomycosis is a disease of immunocompromised amphibians; however, we found no evidence of significant concurrent infection or generalised debility in this common toad. Phaeohyphomycosis appears to be a sporadic cause of mortality in amphibians, and this report adds to the growing list of pathogens known to affect wild amphibians in Europe.

Urban plums and toads: do fleshy fruits affect the post-metamorphic growth of amphibians?

BACKGROUND

The main aim of the study was to analyse the influence of fleshy fruits (plums) on the post-metamorphic growth and feeding behaviour of the green toad Bufotes viridis. We tested the following two hypotheses: (1) juveniles of the green toad are characterised by faster growth in conditions involving fallen plums Prunus cerasifera due to the associated presence of more varied food such as invertebrates; (2) green toads exhibit more active feeding behaviour in the presence of fleshy fruits.

METHODS

A total of 120 fresh metamorphs of the green toad were randomly assigned to one of four groups: two experimental groups with fleshy plums and two other groups as controls (without fruits). Each group was kept in an enclosure to which wild invertebrates had free access. Each individual toad was measured for snout-vent length (mm) and body mass (g) every other day for 30 days. In order to determine whether fallen plums influence the feeding behaviour of toads, the number of active and hidden (under an artificial shelter) individuals was also noted.

RESULTS

The results showed that green toads from both enclosures with plums were characterised by more rapid growth than individuals from the control treatments. Simultaneously, in the enclosure with fleshy fruits, greater species richness of wild invertebrates was observed. No differences in active feeding behaviour were noted between control groups and groups with plums.

DISCUSSION

Fleshy fruits, upon falling, attract many types of invertebrates; thus they may represent good dietary supplements for fresh amphibian metamorphs. Therefore, the presence of fruit trees close to a breeding site might influences the post-metamorphic growth of amphibians, but not their feeding behaviour. The presence of insects associated with fallen fruit seems to favour the occurrence of amphibian populations, which is particularly important, since, due to political and social pressure, numbers of fruit trees are currently being reduced. To our knowledge, no previous study has investigated the potential influence of the presence of fruit trees on the growth and behaviour of anurans.

Bufonid herpesvirus 1 (BfHV1) associated dermatitis and mortality in free ranging common toads (Bufo bufo) in Switzerland

Here we report the discovery and partial characterization of a novel herpesvirus tentatively named Bufonid herpesvirus 1 (BfHV1) from severe dermatitis in free ranging common toads (Bufo bufo) in Switzerland. The disease has been observed in toads every year since 2014, in spring, during the mating season, at different and distant locations. The virus is found in the skin and occasionally in the brain of infected toads. The genome of the virus is at least 158 Kb long and contains at least 152 open reading frames with a minimal length of 270 nt. The genome of BfHV1 contains all the signature genes that are present in alloherpesviruses. Phylogenetic analysis based on the amino acid sequence of the DNA polymerase and terminase proteins positions the novel virus among the members of the genus Batrachovirus, family Alloherpesviridae. This is the first herpesvirus ever characterized in common toads.

Population trend inferred from aural surveys for calling anurans in Korea

Amphibian populations fluctuate naturally in size and range and large datasets are required to establish trends in species dynamics. To determine population trends for the endangered Suweon Treefrog (Dryophytes suweonensis), we conducted aural surveys in 2015, 2016, and 2017 at each of 122 sites where the species was known to occur in the Republic of Korea. Despite being based on individual counts, the focus of this study was to establish population trends rather than population size estimates, and we found both environmental and landscape variables to be significant factors. Encroachment was also a key factor that influenced both the decreasing number of calling individuals and the negative population dynamics, represented here by the difference in the number of calling individuals between years. Generally, most sites displayed minimal differences in the number of calling males between years, although there was a large fluctuation in the number of individuals at some sites. Finally, when adjusted for the overall population size difference between years, we found the population size to be decreasing between 2015 and 2017, with a significant decrease in the number of calling individuals at specific sites. High rate of encroachment was the principal explanatory factor behind these marked negative peaks in population dynamics.

A common toad hybrid zone that runs from the Atlantic to the Mediterranean

We document the distribution of the common toadBufo bufoand the spined toadB. spinosusat their contact zone across France with data from a mitochondrial DNA RFLP assay, complementing similar work including nuclear markers in the northwest and southeast of France and in Italy. We also reconstruct geographical clines across the species’ contact zone in central France.Bufo bufois found in the north-eastern half of France.Bufo spinosusis found in the south-western complement. The contact zone they form runs from the Atlantic coast near Caen, France, to the Mediterranean coast near Savona, Italy, and has a length of over 900 km. In central FranceB. bufoandB. spinosusengage in a hybrid zone with a unimodal genetic signature. Hybrid zone width is ca. 10 km at mitochondrial DNA and averages at 61 km for four nuclear loci. The hybrid zone is distinctly asymmetric with a signature ofB. spinosusinB. bufoand not the other way round. We attribute this observation toB. bufomoving southwards at the expense ofB. spinosus, with introgression in the direction of the advancing species. We noted substantial geographic variation in characters for species identification. Morphological species identification performs well in France, but breaks down in Italy. Mitochondrial DNA is inconclusive in south-eastern France and Italy. The nuclear genetic markers perform consistently well but have not yet been applied to the zone in full. Possible, but surely heterogeneous ecological correlates for the position of the hybrid zone are mountains and rivers.

Differing long term trends for two common amphibian species (Bufo bufo and Rana temporaria) in alpine landscapes of Salzburg, Austria

This study focuses on the population trends of two widespread European anuran species: the common toad (Bufo bufo) and the common frog (Rana temporaria). The basis of this study is data gathered over two decades of amphibian fencing alongside roads in the Austrian state of Salzburg. Different statistical approaches were used to analyse the data. Overall average increase or decrease of each species was estimated by calculating a simple average locality index. In addition the statistical software TRIM was used to verify these trends as well as to categorize the data based on the geographic location of each migration site. The results show differing overall trends for the two species: the common toad being stable and the common frog showing a substantial decline over the last two decades. Further analyses based on geographic categorization reveal the strongest decrease in the alpine range of the species. Drainage and agricultural intensification are still ongoing problems within alpine areas, not only in Salzburg. Particularly in respect to micro-climate and the availability of spawning places these changes appear to have a greater impact on the habitats of the common frog than the common toad. Therefore we consider habitat destruction to be the main potential reason behind this dramatic decline. We also conclude that the substantial loss of biomass of a widespread species such as the common frog must have a severe, and often overlooked, ecological impact.

Inferring microevolution from museum collections and resampling: lessons learned from Cepaea

Natural history collections are an important and largely untapped source of long-term data on evolutionary changes in wild populations. Here, we utilize three large geo-referenced sets of samples of the common European land-snail Cepaea nemoralis stored in the collection of Naturalis Biodiversity Center in Leiden, the Netherlands. Resampling of these populations allowed us to gain insight into changes occurring over 95, 69, and 50 years. Cepaea nemoralis is polymorphic for the colour and banding of the shell; the mode of inheritance of these patterns is known, and the polymorphism is under both thermal and predatory selection. At two sites the general direction of changes was towards lighter shells (yellow and less heavily banded), which is consistent with predictions based on on-going climatic change. At one site no directional changes were detected. At all sites there were significant shifts in morph frequencies between years, and our study contributes to the recognition that short-term changes in the states of populations often exceed long-term trends. Our interpretation was limited by the few time points available in the studied collections. We therefore stress the need for natural history collections to routinely collect large samples of common species, to allow much more reliable hind-casting of evolutionary responses to environmental change.

The prevalence and development of digenean parasites within their intermediate snail host, Galba truncatula, in a geographic area where the presence of Calicophoron daubneyi has recently been confirmed

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C. daubneyi, F. hepatica and H. cylindracea all commonly infect UK G. truncatula.

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C. daubneyi may be less adept at infecting and developing in UK G. truncatula.

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Paramphistomosis risk in the UK may increase if C. daubneyi can adapt to this host.

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Evidence of interactions between digenean species infecting G. truncatula.

During the past decade, rumen fluke (Calicophoron daubneyi) has established as a prominent parasite of livestock within numerous European countries. Its development and spread is enabled by the presence of its intermediate snail host G. truncatula. However, the dynamics of this stage of the C. daubneyi lifecycle is yet to be recorded in numerous northern European countries including the UK. Here, the prevalence of C. daubneyi along with F. hepatica, H. cylindracea and other parasites infecting G. truncatula snails on 10 Welsh farms was recorded using morphological and PCR techniques.

A total of 892 G. truncatula snails were collected between May and October 2016. The prevalence of C. daubneyi in sampled G. truncatula snails (4%) was lower compared to F. hepatica (5.6%). No association in prevalence between these species was recorded. Haplometra cylindracea was found infecting 8.2% of G. truncatula snails, with its prevalence within G. truncatula populations negatively associated with F. hepatica cercariae prevalence (P = 0.004). Generalized estimation equation (GEE) linear regression models identified the levels of respective fluke eggs shed onto pasture as the main significant association between prevalence levels of both C. daubneyi and F. hepatica within G. truncatula populations (P < 0.001). However, equivalent prevalence levels of C. daubneyi and F. hepatica within G. truncatula populations were associated with higher C. daubneyi egg outputs and lower F. hepatica egg outputs from livestock grazing the G. truncatula habitats. Only one of 36C. daubneyi infected G. truncatula snails was found harbouring its cercarial stages, a significantly lower proportion compared to the 29 of 50 F. hepatica infected G. truncatula harbouring its respective cercariae (P < 0.05).

These results signify that C. daubneyi may be less adept at infecting and developing in the UK’s native G. truncatula populations in comparison with F. hepatica. However, C. daubneyi has previously demonstrated its ability to progressively adapt to an intermediate host in a new environment. If C. daubneyi were to adapt to infect and develop more efficiently in UK G. truncatula populations, paramphistomosis risk would significantly increase leading to increased livestock losses. Questions are also raised regarding potential interaction between digenean species at intermediate snail host level, which could impact subsequent livestock trematodosis risk.

Facilitating permeability of landscapes impacted by roads for protected amphibians: patterns of movement for the great crested newt

Amphibian populations are highly vulnerable to road mortality and habitat fragmentation caused by road networks. Wildlife road tunnels are considered the most promising road mitigation measure for amphibians yet generally remain inadequately monitored, resulting in mixed success rates in the short-term and uncertain conservation benefits in the long-term. We monitored a complex multi-tunnel and fence system over five years and investigated the impact of the scheme on movement patterns of two newt species, including the largest known UK population of the great crested newt (Triturus cristatus), a European Protected Species. We used a stage descriptive approach based on capture positions to quantify newt movement patterns. Newt species successfully used the mitigation but the system constituted a bottleneck to movements from the fences to the tunnels. Crossing rates varied widely among years and were skewed towards autumn dispersal rather than spring breeding migration. There was a substantial negative bias against adult male great crested newts using the system. This study indicates that road tunnels could partially mitigate wider connectivity loss and fragmentation at the landscape scale for newt species. However, the observed bottleneck effects and seasonal bias could have population-level effects which must be better understood, especially for small populations, so that improvements can be made. Current requirements for monitoring mitigation schemes post-implementation are probably too short to assess their effectiveness in maintaining connectivity and to adequately understand their population-level impacts.

Population monitoring of a threatened gliding mammal in subtropical Australia

Population monitoring is fundamental to the conservation of threatened species. This study aimed to develop an effective approach for long-term monitoring of the yellow-bellied glider (Petaurus australis) in north-east New South Wales. We conducted repeat surveys to account for imperfect detection and used counts in abundance modelling to produce indices of abundance. We used simulations to explore refinements to our study design. Surveys over three consecutive years produced 195 detections with >95% of detections by call. The probability of detection varied across years and survey occasions, ranging from 0.22 to 0.71. Abundance estimates were remarkably constant across years, ranging from 2.3 ± 0.5 to 2.4 ± 0.6 individuals per site. Occupancy estimates were also constant across years (0.90–0.91). Simulations were run to investigate the influence of the number of surveys (2 or 3) and the number of survey sites (20, 40 or 50) on the probability of occupancy. The design that reduced bias and provided an adequate improvement to precision was that of three visits to 40 survey sites. This design should be adequate to detect a decline in population abundance. Further studies of this kind are needed to better understand the population dynamics of this species.