A Synthesis of Evidence of Drivers of Amphibian Declines

Broad-scale pesticide screening finds anticoagulant rodenticide and legacy pesticides in Australian frogs

Pesticide contamination poses a significant threat to non-target wildlife, including amphibians, many of which are already highly threatened. This study assessed the extent of pesticide exposure in dead frogs collected during a mass mortality event across eastern New South Wales, Australia between July 2021 and March 2022. Liver tissue from 77 individual frogs of six species were analysed for >600 legacy and contemporary pesticides, including rodenticides. More than a third (36 %) of the liver samples contained at least one of the following pesticides: brodifacoum, dieldrin, DDE, heptachlor/heptachlor epoxide, fipronil sulfone, and 2-methyl-4-chlorophenoxyacetic acid (MCPA). Brodifacoum, a second-generation anticoagulant rodenticide, was found in four of the six frog species analysed: the eastern banjo frog (Limnodynastes dumerilii), cane toad (Rhinella marina), green tree frog (Litoria caerulea) and Peron's tree frog (Litoria peronii). This is the first report of anticoagulant rodenticide detected in wild amphibians, raising concerns about potential impacts on frogs and extending the list of taxa shown to accumulate rodenticides. Dieldrin, a banned legacy pesticide, was also detected in two species: striped marsh frog (Limnodynastes peronii) and green tree frog (Litoria caerulea). The toxicological effects of these pesticides on frogs are difficult to infer due to limited comparable studies; however, due to the low frequency of detection the presence of these pesticides was not considered a major contributing factor to the mass mortality event. Additional research is needed to investigate the effects of pesticide exposure on amphibians, particularly regarding the impacts of second-generation anticoagulant rodenticides. There is also need for continued monitoring and improved conservation management strategies for the mitigation of the potential threat of pesticide exposure and accumulation in amphibian populations.

Comparing skin swabs, buccal swabs, and toe clips for amphibian genetic sampling, a case study with a small anuran (Acris blanchardi)

Multiple methods for collecting genetic samples from amphibians exist, each with their own implications for study design, animal welfare, and costs. Toe clipping is one common method, but there is ongoing debate regarding its potential detriment. Less invasive methods should be implemented, if efficacious, as amphibians are a particularly vulnerable vertebrate group. Skin and buccal swabbing are less invasive methods for genetic sampling, but the potential for contamination and a lower yield of DNA may exist. To compare these methods, we gathered skin swabs, buccal swabs, and toe clips from the same individuals of a relatively small anuran species, Blanchard's Cricket Frog (Acris blanchardi). We then compared DNA yield, DNA purity, amplification success rate, and genotypic data quality among sample types. We found toe clips and buccal swabs generated similar DNA yield and purity, with skin swabs yielding significantly less DNA of significantly lower purity than the other sample types. Amplification success rate was significantly higher using toe clips compared to the other sample types, though buccal swab samples amplified more readily than skin swabs. Genotypic data from toe clips and buccal swabs did not differ significantly in quality, but skin swab data quality was significantly lowest among sample types. Thus, skin swabbing could produce erroneous data in some situations, but buccal swabbing is likely an effective substitute to toe clipping, even for small species. Our results can help future researchers select which genetic sampling method might best suit their research needs.

Microplastics and TiO2 nanoparticles mixture as an emerging threat to amphibians: A case study on bullfrog embryos

Emerging contaminants can act as contributing factors to the decline of amphibian populations worldwide. Recently, scientists have drawn attention to the potential ecotoxicity of microplastics and nanomaterials in amphibians, however, their possible effects on embryonic developmental stages are still absent. Thus, the present study analyzed the developmental toxicity of environmentally relevant concentrations of polyethylene microplastics (PE MPs; 60 mg/L) and titanium dioxide nanoparticles (TiO2 NPs; 10 μg/L), isolated or in combination (Mix group) on bullfrog embryos, Aquarana catesbeiana, adapting the Frog Embryo Teratogenesis Assay (FETAX, 96h). Allied to the FETAX protocol, we also analyzed the heart rate and morphometric data. The exposure reduced the survival and hatching rates in groups exposed to TiO2 NPs, and to a lesser extent, also affected the Mix group. TiO2 NPs possibly interacted with the hatching enzymes of the embryos, preventing hatching, and reducing their survival. The reduced effects in the Mix group are due to the agglomeration of both toxicants, making the NPs less available for the embryos. PE MPs got attached to the gelatinous capsule of the chorion (confirmed by fluorescence microscopy), which protected the embryos from eventual direct effects of the microplastics on the hatching and survival rates. Although there were no cardiotoxic effects nor morphometric alterations, there was a significant increase in abdominal edemas in the hatched embryos of the PE MPs group, which indicates that osmoregulation might have been affected by the attachment of the microplastics on the embryos' gelatinous capsule. This study presents the first evidence of developmental toxicity of environmental mixtures of microplastics and nanoparticles on amphibians and reinforces the need for more studies with other amphibian species, especially neotropical specimens that could present bigger sensibility. Our study also highlighted several features of the FETAX protocol as useful tools to evaluate the embryotoxicity of several pollutants on amphibians.

Estrogen contamination increases vulnerability of amphibians to the deadly chytrid fungus

Aquatic contaminants and infectious diseases are among the major drivers of global amphibian declines. However, the interaction of these factors is poorly explored and could better explain the amphibian crisis. We exposed males and females of the Brazilian Cururu Toad, Rhinella icterica, to an environmentally relevant concentration of the estrogen 17-alpha-ethinylestradiol (an emerging contaminant) and to the chytrid infection (Batrachochytrium dendrobatidis), in their combined and isolated forms, and the ecotoxicity was determined by multiple biomarkers: cutaneous, hematological, cardiac, hepatic, and gonadal analysis. Our results showed that Cururu toads had many physiological alterations in response to the chytrid infection, including the appearance of cutaneous Langerhans's cells, increased blood leukocytes, increased heart contraction force and tachycardia, increased hepatic melanomacrophage cells, which in turn led to gonadal atrophy. The estrogen, in turn, increased the susceptibility of the toads to the chytrid infection (higher Bd loads) and maximized the deleterious effects of the pathogen: reducing leukocytes, decreasing the contraction force, and causing greater tachycardia, increasing hepatic melanomacrophage cells, and leading to greater gonadal atrophy, which were more extreme in females. The exposure to estrogen also revealed important toxicodynamic pathways of this toxicant, as shown by the immunosuppression of exposed animals, and the induction of the first stages of feminization in males, which corroborates that the synthetic estrogen acts as an endocrine disruptor. Such an intricate relationship is unprecedented and reinforces the importance of studying the serious consequences that multiple environmental stressors can cause to aquatic populations.

The effects of preformed vitamin A and provitamin A carotenoid supplementation on tadpoles of the poison frog Phyllobates vittatus

Understanding the nutritional requirements of captive animals is necessary for proper animal husbandry, however, the specific dietary requirements for many amphibian species commonly kept in captivity are unknown. Like most vertebrates, frogs cannot synthesize carotenoids and must therefore obtain these essential nutrients through diet. It is unclear if amphibians can cleave provitamin A carotenoids to form vitamin A metabolically within the body, so common practice is to supplement their captive diets with both preformed vitamin A and provitamin A carotenoids. We carried out a feeding experiment in tadpoles of Phyllobates vittatus, a commonly kept poison frog species, to test the effects of supplementing a fish flake diet with a provitamin A carotenoid (2.5 mg/g β-carotene) and vitamin A (0.033-0.066 µg/mL retinyl acetate), both individually and in combination. Contrary to our expectations, supplementation had either no effect or adverse effects on tadpole growth and survivorship. Tadpoles reared under supplemented diets with vitamin A showed higher mortality rates, coupled with symptoms of hypervitaminosis A. Survivors had a smaller body size and mass at metamorphosis. β-carotene supplementation alone had no detectable effect. The vitamin A and β-carotene levels in our supplemented diet have been shown to be harmless or benefit tadpoles of other species, yet our results indicate that adding these amounts to what is found in a generalist fish flake mix can have detrimental effects on P. vittatus tadpoles. More broadly, this study highlights the importance of creating husbandry guidelines based on the specific physiological needs of the species (or species groups) being kept in captivity, rather than general ones for all amphibians, as is often done.

The habitat quality paradox: loss of riparian forest cover leads to decreased risk of parasitism and improved body condition in an imperiled amphibian

Amphibian declines are a global phenomenon but responses of populations to specific threats are often context dependent and mediated by individual physiological condition. Habitat degradation due to reduced riparian forest cover and parasitism are two threats facing the hellbender salamander (Cryptobranchus alleganiensis), but their potential to interact in nature remains largely unexplored. We investigated associations between forest cover, parasitic infection and physiology of hellbenders to test the hypotheses that physiological condition responds to infection and/or habitat degradation. We sampled 17 stream reaches in southwest Virginia, USA, on a year-round basis from 2013 to 2016 and recorded 841 captures of 405 unique hellbenders. At each capture we documented prevalence of two blood-associated parasites (a leech and trypanosome) and quantified up to three physiological condition indices (body condition, hematocrit, white blood cell [WBC] differentials). We used generalized linear mixed models to describe spatiotemporal variation in parasitic infection and each condition index. In general, living in the most heavily forested stream reaches, where hellbender density was highest, was associated with the greatest risk of parasitism, elevated neutrophil-to-lymphocyte (N:L) ratios and eosinophils, slightly lower hematocrit and lower mean body condition in hellbenders. All condition indices fluctuated temporally in a manner consistent with seasonal variation in hellbender metabolic demands and breeding phenology and were associated with land use during at least part of the year. Paradoxically, relatively low levels of forest cover appeared to confer a potential advantage to individuals in the form of release from parasites and improved body condition. Despite improved body condition, individuals from less forested areas failed to exhibit fluctuating body condition in response to spawning, which was typical in hellbenders from more forested habitats. We postulate this lack of fluctuation could be due to reduced conspecific competition or reproductive investment and/or high rates of filial cannibalism in response to declining forest cover.

Cross-species gut microbiota transplantation predictably affects host heat tolerance

The gut microbiome is known to influence and have regulatory effects in diverse physiological functions of host animals, but only recently has the relationship between host thermal biology and gut microbiota been explored. Here, we examined how early-life manipulations of the gut microbiota in larval amphibians influenced their critical thermal maximum (CTmax) at different acclimation temperatures. We stripped the resident microbiome from egg masses of wild-caught wood frogs (Lithobates sylvaticus) via an antibiotic wash, and then inoculated the eggs with pond water (control), no inoculation, or the intestinal microbiota of another species that has a wider thermal tolerance - green frogs (Lithobates clamitans). We predicted that this cross-species transplant would increase the CTmax of the recipient wood frog larvae relative to the other treatments. In line with this prediction, green frog microbiome-recipient larvae had the highest CTmax while those with no inoculum had the lowest CTmax. Both the microbiome treatment and acclimation temperature significantly influenced the larval gut microbiota communities and α-diversity indices. Green frog microbiome-inoculated larvae were enriched in Rikenellaceae relative to the other treatments, which produce short-chain fatty acids and could contribute to greater energy availability and enhanced heat tolerance. Larvae that received no inoculation had a higher relative abundance of potentially pathogenic Aeromonas spp., which negatively affects host health and performance. Our results are the first to show that cross-species gut microbiota transplants alter heat tolerance in a predictable manner. This finding has repercussions for the conservation of species that are threatened by climate change and demonstrates a need to further explore the mechanisms by which the gut microbiota modulate host thermal tolerance.

The role of Culex territans mosquitoes in the transmission of Batrachochytrium dendrobatidis to amphibian hosts

BACKGROUND

Mosquitoes are the deadliest organisms in the world, killing an estimated 750,000 people per year due to the pathogens they can transmit. Mosquitoes also pose a major threat to other vertebrate animals. Culex territans is a mosquito species found in temperate zones worldwide that feeds almost exclusively on amphibians and can transmit parasites; however, little is known about its ability to transmit other pathogens, including fungi. Batrachochytrium dendrobatidis (Bd) is a topical pathogenic fungus that spreads through contact. With amphibian populations around the world experiencing mass die-offs and extinctions due to this pathogen, it is critical to study all potential modes of transmission. Because Cx. territans mosquitoes are in contact with their hosts for long periods of time while blood-feeding, we hypothesize that they can transmit and pick up Bd.

METHODS

In this study, we first assessed Cx. territans ability to transfer the fungus from an infected surface to a clean one under laboratory conditions. We also conducted a surveillance study of Bd infections in frogs and mosquitoes in the field (Mountain Lake Biological station, VA, USA). In parallel, we determined Cx. territans host preference via blood meal analysis of field caught mosquitoes.

RESULTS

We found that this mosquito species can carry the fungus to an uninfected surface, implying that they may have the ability to transmit Bd to their amphibian hosts. We also found that Cx. territans feed primarily on green frogs (Rana clamitans) and bullfrogs (Rana catesbeiana) and that the prevalence of Bd within the frog population at our field site varied between years.

CONCLUSIONS

This study provides critical insights into understanding the role of amphibian-biting mosquitoes in transmitting pathogens, which can be applied to disease ecology of susceptible amphibian populations worldwide.

Warmer temperature overrides the effects of antidepressants on amphibian metamorphosis and behavior

Climate change can exacerbate the effects of environmental pollutants on aquatic organisms. Pollutants such as human antidepressants released from wastewater treatment plants have been shown to impact life-history traits of amphibians. We exposed tadpoles of the wood frog Lithobates sylvaticus to two temperatures (20 °C and 25 °C) and two antidepressants (fluoxetine and venlafaxine), and measured timing of metamorphosis, mass at metamorphosis, and two behaviors (startle response and percent motionless). Antidepressants significantly shortened time to metamorphosis at 20 °C, but not at 25 °C. At 25 °C, tadpoles metamorphosed significantly faster than those at 20 °C independent of antidepressant exposure. Venlafaxine reduced body mass at 25 °C, but not at 20 °C. Temperature and antidepressant exposure affected the percent of tadpoles showing a startle response. Tadpoles at 20 °C displayed significantly more responses than at 25 °C. Exposure to fluoxetine also increased the percent of tadpoles showing a startle response. Venlafaxine reduced the percent of motionless tadpoles at 25 °C but not at 20 °C. While our results showed that antidepressants can affect the timing of metamorphosis in tadpoles, warmer temperatures overrode these effects and caused a reduction in an important reaction behavior (startle response). Future studies should address how warmer global temperatures may exacerbate or negate the effects of environmental pollutants.

Assay validation of saliva glucocorticoids in Columbia spotted frogs and effects of handling and marking

Non-invasive methods are important to the field of conservation physiology to reduce negative effects on organisms being studied. Glucocorticoid (GC) hormones are often used to assess health of individuals, but collection methods can be invasive. Many amphibians are imperiled worldwide, and saliva is a non- or semi-invasive matrix to measure GCs that has been partially validated for only four amphibian species. Validation ensures that assays are reliable and can detect changes in saliva corticosterone (sCORT) after exposure to stressors, but it is also necessary to ensure sCORT concentrations are correlated with plasma concentrations. To help validate the use of saliva in assessing CORT responses in amphibians, we captured uniquely marked Columbia spotted frogs (Rana luteiventris) on sequential days and collected baseline and stress-induced (after handling) samples. For a subset of individuals, we collected and quantified CORT in both saliva and blood samples, which have not been compared for amphibians. We tested several aspects of CORT responses and, by collecting across separate days, measured repeatability of CORT responses across days. We also evaluated whether methods common to amphibian conservation, such as handling alone or handling, clipping a toe and tagging elevated sCORT. Similar to previous studies, we show that sCORT is reliable concerning parallelism, recovery, precision and sensitivity. sCORT was weakly correlated with plasma CORT (R2 = 0.21), and we detected elevations in sCORT after handling, demonstrating biological validation. Toe clipping and tagging did not increase sCORT over handling alone, but repeated handling elevated sCORT for ~72 hours. However, sCORT responses were highly variable and repeatability was low within individuals and among capture sessions, contrary to previous studies with urinary and waterborne CORT. sCORT is a semi-invasive and rapid technique that could be useful to assess effects of anthropogenic change and conservation efforts, but will require careful study design and future validation.

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.

Interdisciplinary approach to solve unusual mortalities in the European common frog (Rana temporaria) in two high-mountain ponds affected by climate change

The global decline in amphibian populations is a major environmental issue. Chytridiomycosis, Ranaviruses and the red-leg syndrome have been identified in unusual mortality events. However, these infections do not account for all causes of declining amphibian populations. Moreover, several cases of amphibian mortality are difficult to solve without resorting to an interdisciplinary approach. Two cases of unusual mortality in Rana temporaria occurred at two high-mountain ponds (northwest Italy) in April and May 2021. Water and frog samples were analysed to understand the possible causes responsible for the unusual mortalities. Results of the main physicochemical (pH, conductivity, dissolved oxygen, chemical and biochemical oxygen demand) and nutrient (ammonia/ammonium, nitrite, nitrate, total phosphorus) parameters revealed a good condition of the water quality, with the absence of the main cyanotoxins (microcystins/nodularins). However, unseasonably high spring water temperatures were recorded in both ponds (12.73 °C and 14.21 °C for Frog Pond and Selleries Pond, respectively). Frogs (n = 50; snout-vent length: 7.0-9.8 cm; body mass: 85-123 g) collected from Frog Pond mainly presented bumps on the ventral cavity and dermal ulceration associated with the isolation of Carnobacterium maltaromaticum. On the other hand, frogs (n = 5; snout-vent length: 8.0-9.1 cm; body mass: 87-92 g) from Selleries Pond presented petechiae and dermal ulcerations on the rear limbs associated with the isolation of Aeromonas salmonicida and A. sobria. In both mortality events, the interdisciplinary approach revealed an association between frog mortalities and the isolation of bacteria. Isolated bacteria are considered opportunistic pathogens, and the high values of the water temperature has certainly led a stress on the frogs, favouring the spread of bacteria and the death of the frogs. Further studies are needed to assess the pathophysiological effects of the opportunistic bacteria here isolated, clarifying the interactions between emerging pathogens and climate change.

Heat hardening of a larval amphibian is dependent on acclimation period and temperature

Plasticity in heat tolerance provides ectotherms the ability to reduce overheating risk during thermal extremes. However, the tolerance-plasticity trade-off hypothesis states that individuals acclimated to warmer environments have a reduced plastic response, including hardening, limiting their ability to further adjust their thermal tolerance. Heat hardening describes the short-term increase in heat tolerance following a heat shock that remains understudied in larval amphibians. We sought to examine the potential trade-off between basal heat tolerance and hardening plasticity of a larval amphibian, Lithobates sylvaticus, in response to differing acclimation temperatures and periods. Lab-reared larvae were exposed to one of two acclimation temperatures (15°C and 25°C) for either 3 or 7 days, at which time heat tolerance was measured as critical thermal maximum (CT_max ). A hardening treatment (sub-critical temperature exposure) was applied 2 h before the CT_max assay for comparison to control groups. We found that heat-hardening effects were most pronounced in 15°C acclimated larvae, particularly after 7 days of acclimation. By contrast, larvae acclimated to 25°C exhibited only minor hardening responses, while basal heat tolerance was significantly increased as shown by elevated CT_max temperatures. These results are in line with the tolerance-plasticity trade-off hypothesis. Specifically, while exposure to elevated temperatures induces acclimation in basal heat tolerance, shifts towards upper thermal tolerance limits constrain the capacity for ectotherms to further respond to acute thermal stress.

Cryptic lineages and standing genetic variation across independent cane toad introductions

Widespread introduced species can be leveraged to investigate the genetic, ecological and adaptive processes underlying rapid evolution and range expansion, particularly the contributions of genetic diversity to adaptation. Rhinella marina, the cane toad, has been a focus of invasion biology for decades in Australia. However, their introduction history in North America is less clear. Here, we investigated the roles of introduction history and genetic diversity in establishment success of cane toads across their introduced range. We used reduced representation sequencing (ddRAD) to obtain 34,000 SNPs from 247 toads in native (French Guiana, Guyana, Ecuador, Panama, Texas) and introduced (Bermuda, southern Florida, northern Florida, Hawai'i, Puerto Rico) populations. Unlike all other cane toad introductions, we found that Florida populations were more closely related to native Central American lineages (R. horribilis), than to native Southern American lineages (R. marina). Furthermore, we found high levels of diversity and population structure in the native range, corroborating suggestions that R. marina is a species complex. We also found that introduced populations exhibit only slightly lower genetic diversity than native populations. Together with demographic analyses, this indicates founding populations of toads in Florida were larger than previously reported. Lastly, within R. marina, only one of 245 putatively adaptive SNPs showed fixed differences between native and introduced ranges, suggesting that putative selection in these introduced populations is based upon existing genetic variation. Our findings highlight the importance of genetic sequencing in understanding biological introductions and hint at the role of standing genetic variation in range expansion.

Artificialwater bodies as amphibian breeding sites: the case of the common midwife toad (Alytes obstetricans) in central Spain

Natural breeding sites for amphibians are decreasing in quantity and quality in temperate regions, resulting in local extinctions and increasing population fragmentation. Artificial water bodies (e.g., water tanks or cattle troughs) can represent suitable reproductive habitats for some amphibians, but demographic data are required to assess this assumption. We evaluated the role of artificial water bodies in the persistence of a species of population concern, the common midwife toad, Alytes obstetricans (Laurenti, 1768), at local and regional scales. We surveyed 275 water bodies to characterize the distribution of the species and detected 63 breeding populations of A. obstetricans where we estimated larval abundance. In addition, we monitored two populations for three consecutive breeding seasons using capture-mark-recapture methods based on photo-identification, assessing abundance, breeding success and the use of space of adult individuals captured on multiple occasions. Our results show that artificial sites are preferentially used as breeding sites in the region compared to natural aquatic habitats, providing key habitat for the species and hosting much larger numbers and densities of larvae than natural sites. At local scale, populations of A. obstetricans in artificial sites were abundant and characterized by high male breeding success. However, adults are spatially aggregated around breeding sites, with small home ranges, implying high vulnerability to population fragmentation. Our results suggest artificial breeding sites can sustain viable populations of A. obstetricans, provided measures promoting connectivity among breeding nuclei are considered.

The Effects of Artificial Night Lighting on Tail Regeneration and Prey Consumption in a Nocturnal Salamander (Plethodon cinereus) and on the Behavior of Fruit Fly Prey (Drosophila virilis)

Simple Summary

Amphibians, including salamanders, are declining worldwide at an alarming rate due to a variety of factors that include habitat decline and destruction and environmental pollutants. Artificial light at night (ALAN) due to human activities is a nearly ubiquitous pollutant and can have serious consequences for amphibians. We examined the impact of ecologically-relevant levels of ALAN on tail regeneration in the eastern red-backed salamander, prey consumption by these salamanders and behavior of their fruit fly prey. We found that ALAN reduced the rate of salamander tail regeneration at some light levels above the naturally dark nocturnal illumination and increased the activity of their prey but not always in a simple, linear fashion. Thus, ALAN, even at very low levels, can influence the physiology and regeneration of a nocturnal salamander.

Abstract

As human development continues to encroach into natural habitats, artificial light at night (ALAN) has increasingly become a concern for wildlife. Nocturnal animals are especially vulnerable to ALAN, as the physiology and behavior of nocturnal species have evolved under conditions associated with predictably dark environments. Studies exposing amphibians to constant bright light provide evidence for changes to normal metabolism, growth, and behavior, but few of these studies have used treatments of dim ALAN comparable to that found in affected habitats. Eastern red-backed salamanders, Plethodon cinereus, use their tails for fat storage and communication, are capable of tail autotomy as an antipredator mechanism, and can regenerate the tail in its entirety. We examined the effect of different, ecologically-relevant intensities of ALAN on the rate of tail regeneration in adult P. cinereus. We hypothesized that ALAN would increase tail regeneration rates such that salamanders exposed to higher levels of light at night would regenerate tails faster than those exposed to lower light levels. In a controlled laboratory setting, we exposed salamanders (N = 76) in test chambers to nocturnal illuminations of 0.0001 lx (no ALAN, natural nocturnal illumination dark control), 0.01 lx (weak ALAN), 1 lx (moderate ALAN), or 100 lx (bright ALAN, equal to dim daytime and our day lighting treatment) for a period of 90 d immediately following tail autotomy. In addition, because these salamanders eat mostly live, moving prey, we investigated the impact of ALAN on the behavior of prey (Drosophila virilis) fed to the salamanders in our laboratory trials, which could alter feeding and regeneration rates in salamanders. We predicted that prey consumption would not be affected by ALAN and measured both prey consumption and prey behavior (activity) to examine the potential influence on regeneration. For tail regeneration, we found a non-monotonic response to ALAN, with salamanders exposed to nocturnal illuminations 0.1 lx and 100 lx regenerating tails significantly slower than salamanders in the 0.0001 lx or 1 lx treatments. Prey consumption did not differ among light treatments; however, fruit fly activity increased with increasing ALAN. These results suggest that ALAN influences regeneration rates, but the rate of regeneration is not dose-dependent and is not explained easily by prey consumption or movement of prey. We suggest that tail regeneration in these salamanders may involve a complex mechanism of altered gene expression and/or modulation of hormonal activity (corticosterone, melatonin, serotonin, and/or prolactin) at different intensities of nocturnal lighting.

Cheruiyot. Breeding phenology and population dynamics of the endangered Forest Spiny Reed Frog Afrixalus sylvaticus Schiøtz, 1974 in Shimba Hills, Kenya

Afrixalus sylvaticus Schiøtz, 1974 is a species of hyperoliid frog inhabiting coastal forest Kenya. It is classified as endangered under IUCN B2ab(iii) ver 3.1 and occurs in the Shimba Hills National Park and hinterlands. Habitat loss and other human activities are threatening the species. Therefore, understanding the breeding ecology and population dynamics is important for its conservation. This study assessed the breeding ecology and population dynamics of the species in the protected and community landscapes in Shimba Hills National Reserve in Kenya. Data was collected through ecological surveys conducted from June 2016 to July 2017 using a visual encounter surveys (VES) method. The results show that the species was more abundant during the wet season than dry (58% and 42%, respectively). The population estimate was 192 individuals and a density of 0.98 individuals/km2. Regarding the morphology, the mean snout-vent length (SVL) for males was 15.12 mm and females 15.96 mm, but there was no significant difference (t-test = 0.87, p = 0.390, df = 39). The mean weight of both gravid and non-gravid females was 6.05 g and males was 4.82 g. The weights were statistically different between both sexes (t-test = 3.50, p-value = 0.001, df = 39). The sex ratio was 1:2 (male: female). There was more activity in the wet season (April and May), and the breeding habitats were reeds and water lilies. The threats identified to their habitat include; human activities such as bush burning, livestock grazing, drainage, and plantation of exotic tree species (Eucalyptus sp.) that have led to habitat loss and degradation. The study recommends that the reforestation processes such as plantation of exotic species such as Eucalyptus sp. and Casuarina sp. and bush burning in the wetlands and species habitats must be discouraged among the stakeholders (community and park management). Moreover, more synchronized studies are necessary to highlight the driver(s) of imbalanced sex ratios and species habitat shifts.

Toxicity and genotoxicity of imidacloprid in the tadpoles of Leptodactylus luctator and Physalaemus cuvieri (Anura: Leptodactylidae)

Imidacloprid is a neonicotinoid insecticide used to control agricultural pests around the world. This pesticide can have adverse effects on non-target organisms, especially in aquatic environments. The present study evaluated the toxicity of an imidacloprid-based insecticide in amphibians, using Leptodactylus luctator and Physalaemus cuvieri tadpoles as study models. Spawning of both species were collected within less than 24 h of oviposition from a non-agricultural land at Erechim, Rio Grande do Sul state, Brazil. Survival, swimming activity, body size, morphological malformations, and genotoxic parameters were analyzed at laboratory conditions. A short-term assay was conducted over 168 h (7 days) with five different concentrations of imidacloprid (3–300 µg L⁻¹) being tested. The insecticide did not affect survival, although the tadpoles of both species presented reduced body size, malformed oral and intestine structures, and micronuclei and other erythrocyte nuclear abnormalities following exposure to this imidacloprid-based compound. Exposure also affected swimming activity in L. luctator, which reflected the greater sensitivity of L. luctator to imidacloprid in comparison with P. cuvieri. The swimming activity, body size, and malformations observed in L. luctator and the morphological malformations found in P. cuvieri indicated that even the lowest tested concentration of the insecticide were harmful to amphibians. At concentrations of over 3 μg L⁻¹, P. cuvieri presents a smaller body size, and both species are affected by genotoxic cell damage. This demonstrates that imidacloprid is potentially toxic for the two study species at environmentally relevant concentrations.

Biodiversity Monitoring of a Riparian Wetland in a Mixed-Use Watershed in the Central Appalachians, USA, before Restoration

Wetland mitigation efforts have increased in numbers over the past two decades to combat wetland loss in the United States. Data regarding wetland function such as biodiversity are required to be collected 5–10 years after a project is complete; however, pre-restoration data that can inform the effectiveness of mitigation are often not collected. We conducted pre-restoration surveys on various taxa along or within Ruby Run, a tributary of Deckers Creek in north-central West Virginia, USA, from 2016 to 2020 to determine the baseline relative abundance and diversity within the stream and the associated riparian zone. In five years, we observed 237 species (154 plant, 58 bird, 13 fish, 6 small mammal, and 6 anuran) and 25 families of macroinvertebrates. Seasonal fluctuations in diversity were present, but mean diversity was relatively consistent among years across taxa, except in anurans, where there was a decrease each year. Wetland mitigation efforts should continue to be monitored for success using multiple taxa, because land use change can affect taxa in different ways, resulting in well-rounded assessments that can improve wetland management practices.

Comparison of POCIS and grab sampling techniques for monitoring PPCPs in vernal pools in central Pennsylvania

Active ingredients in pharmaceuticals and personal care products (PPCPs) can persist through wastewater treatment plants and be released into the environment where they can inadvertently pose risks to non-target organisms. Emerging contaminants (ECs), including PPCPs, are commonly detected in wastewater effluent. With the increasing beneficial re-use of treated wastewater globally, there is a need to understand how spray-irrigation activities affect the occurrence and persistence of ECs in the environment to which they are introduced. Here, we explore the impacts of wastewater spray-irrigation on nearby ephemeral wetlands (e.g., vernal pools) through the use of grab and Polar Organic Chemical Integrative Sampling (POCIS) techniques. This study sought to determine whether integrative sampling techniques are better suited than traditional grab sampling techniques in assessing the presence and concentrations of ECs in vernal pools by evaluating 34 ECs in six vernal pools in central Pennsylvania. Three pools were impacted by wastewater spray-irrigation activities and three were in a nearby forested area. Results of this study found that POCIS detected a wide range of 25 ECs (log K_ow between -2.6 and 9.37) more or, in some cases, equally frequently, relative to grab samples. Additionally, grab samples were found to best capture short-lived elevated inputs of ECs (from irrigation events) while POCIS were found to best capture ECs that were present in vernal pools over a longer period of time (weeks to months). For ECs detected more frequently in grab samples, concentrations were higher compared to time weighted average aqueous concentrations estimated from POCIS. This study advances understanding of the potential impact of wastewater beneficial reuse on vernal pools and informs how best to monitor the presence of ECs in vernal pools using integrative and grab sampling techniques.

Early life skin microbial trajectory as a function of vertical and environmental transmission in Bornean foam-nesting frogs

BACKGROUND

The amphibian skin microbiome is an important mediator of host health and serves as a potential source of undiscovered scientifically significant compounds. However, the underlying modalities of how amphibian hosts obtain their initial skin-associated microbiome remains unclear. Here, we explore microbial transmission patterns in foam-nest breeding tree frogs from Southeast Asia (Genus: Polypedates) whose specialized breeding strategy allows for better delineation between vertically and environmentally derived microbes. To facilitate this, we analyzed samples associated with adult frog pairs taken after mating-including adults of each sex, their foam nests, environments, and tadpoles before and after environmental interaction-for the bacterial communities using DNA metabarcoding data (16S rRNA). Samples were collected from frogs in-situ in Brunei, Borneo, a previously unsampled region for amphibian-related microbial diversity.

RESULTS

Adult frogs differed in skin bacterial communities among species, but tadpoles did not differ among species. Foam nests had varying bacterial community composition, most notably in the nests' moist interior. Nest interior bacterial communities were discrete for each nest and overall displayed a narrower diversity compared to the nest exteriors. Tadpoles sampled directly from the foam nest displayed a bacterial composition less like the nest interior and more similar to that of the adults and nest exterior. After one week of pond water interaction the tadpole skin microbiome shifted towards the tadpole skin and pond water microbial communities being more tightly coupled than between tadpoles and the internal nest environment, but not to the extent that the skin microbiome mirrored the pond bacterial community.

CONCLUSIONS

Both vertical influence and environmental interaction play a role in shaping the tadpole cutaneous microbiome. Interestingly, the interior of the foam nest had a distinct bacterial community from the tadpoles suggesting a limited environmental effect on tadpole cutaneous bacterial selection at initial stages of life. The shift in the tadpole microbiome after environmental interaction indicates an interplay between underlying host and ecological mechanisms that drive community formation. This survey serves as a baseline for further research into the ecology of microbial transmission in aquatic animals.

Retrospective Survey of Amphibian Pathology Cases at Texas A&M University System (2016-2020)

Dramatic declines in amphibians worldwide highlight the need for a better understanding of diseases affecting these species. To delineate the health issues of amphibians submitted to Texas A&M University System (2016-2020), the databases were queried on the basis of defined selection criteria. A total of 502 anurans (157 frogs [44 species] and 345 toads [10 species]) and 30 caudatans (23 salamanders [6 species] and 7 newts [4 species]) were reviewed. A most likely cause of death or major pathological finding (CD-MPF) leading to euthanasia was identified in 295 (55%) Anura cases and 15 (50%) Caudata cases. Of the 532 records reviewed, anurans included 492 captive, seven free-ranging and three undetermined specimens. All caudatans were captive. The most common CD-MPF in anurans was infectious/inflammatory (228/295; 77%), involving mycobacteriosis (73/228; 32%), chlamydiosis (44/228; 19%) and mycosis (32/228; 14%). Neoplasia was less common (28/295; 9%). Infectious/inflammatory lesions (14/15; 93%) were the main CD-MPFs in caudatans. Infectious diseases are a significant threat to captive amphibians in Texas and these results may aid personnel involved in amphibian conservation programmes, veterinarians and diagnosticians.

Design of Protected Area by Tracking and Excluding the Effects of Climate and Landscape Change: A Case Study Using Neurergus derjugini

This study aimed to use the applications of Ensemble Species Distribution Modelling (eSDM), Geographical Information Systems (GISs), and Multi-Criteria Decision Analysis (MCDA) for the design of a protected area (PA) for the critically endangered yellow-spotted mountain newt, Neurergus derjugini, by tracking and excluding the effects of climate and landscape changes in western Iran and northeastern Iraq. Potential recent and future distributions (2050 and 2070) were reconstructed by eSDM using eight algorithms with MRI-CGCM3 and CCSM4 models. The GIS-based MCDA siting procedure was followed inside habitats with high eSDM suitability by eliminating the main roads, cities, high village density, dams, poor vegetation, low stream density, agricultural lands and high ridge density. Then, within the remaining relevant areas, 10 polygons were created as “nominations” for PAs (NPAs). Finally, for 10 different NPAs, the suitability score was ranked based on ratings and weights (analytical hierarchy process) of the number of newt localities, NPA connectivity, NPA shape, NPA habitat suitability in 2070, NPA size, genetic diversity, village density and distance to nearest PAs, cities, and main roads. This research could serve as a modern realistic approach for environmental management to plan conservation areas using a cost-effective and affordable technique.

Primary Hepatic Vascular Neoplasm in a Houston Toad (Anaxyrus houstonensis)

An 11-year-old captive, female Houston toad (Anaxyrus houstonensis) became lethargic and reluctant to move. This toad had been administered human chorionic gonadotropin (HCG) and luteinizing hormone-releasing hormone (LHRH) annually as part of a hormone-assisted captive propagation programme for 8 years. Due to poor prognosis, euthanasia was elected. At necropsy, the liver was moderately enlarged, diffusely dark red and had a nodular superficial appearance. Microscopically, the hepatic nodules consisted of poorly demarcated, non-encapsulated, paucicellular infiltrative neoplastic growths. These consisted of spindle cells, similar to sinusoidal endothelial cells, that formed irregular blood-filled vascular channels resembling sinusoids separated by thin bands of collagen and reticulin fibres. Neoplastic cells dissected through and replaced hepatic cords and bile ducts. Based on the cytohistomorphological features and analogy with vascular neoplasms in other vertebrates, a diagnosis of low-grade angiosarcoma was made. To the best of our knowledge, this is the first record of primary hepatic vascular neoplasia in an amphibian. It is not known if the long-term administration of HCG and LHRH had any oncogenic role in this animal. Vascular neoplasia should be included in the differential diagnosis of hepatomegaly and non-specific lethargy and health decline in amphibian species.