Patterns of amphibian infection prevalence across wetlands on the Savannah River Site, South Carolina, USA.

Amphibian diseases, such as chytridiomycosis caused by Batrachochytrium dendrobatidis (Bd) and ranaviral disease caused by ranaviruses, are often linked to global amphibian population declines, yet the ecological dynamics of both pathogens are poorly understood. The goal of our study was to determine the baseline prevalence, pathogen loads, and co-infection rate of Bd and ranavirus across the Savannah River Site (SRS) in South Carolina, USA, a region with rich amphibian diversity and a history of amphibian-based research. We tested over 1000 individuals, encompassing 21 amphibian species from 11 wetlands for both Bd and ranavirus. The prevalence of Bd across individuals was 9.7%. Using wetland means, the mean (±SE) Bd prevalence was 7.9 ± 2.9%. Among toad species, Anaxyrus terrestris had 95 and 380% greater odds of being infected with Bd than Scaphiopus holbrookii and Gastrophryne carolinensis, respectively. Odds of Bd infection in adult A. terrestris and Lithobates sphenocephalus were 75 to 77% greater in metal-contaminated sites. The prevalence of ranavirus infections across all individuals was 37.4%. Mean wetland ranavirus prevalence was 29.8 ± 8.8% and was higher in post-metamorphic individuals than in aquatic larvae. Ambystoma tigrinum had 83 to 85% higher odds of ranavirus infection than A. opacum and A. talpoideum. We detected a 4.8% co-infection rate, with individuals positive for ranavirus having a 5% higher occurrence of Bd. In adult Anaxyrus terrestris, odds of Bd infection were 13% higher in ranavirus-positive animals and odds of co-infection were 23% higher in contaminated wetlands. Overall, we found the pathogen prevalence varied by wetland, species, and life stage.

Fundamentals of wildlife dosimetry and lessons learned from a decade of measuring external dose rates in the field.

Methods for determining the radiation dose received by exposed biota require major improvements to reduce uncertainties and increase precision. We share our experiences in attempting to quantify external dose rates to free-ranging wildlife using GPS-coupled dosimetry methods. The manuscript is a primer on fundamental concepts in wildlife dosimetry in which the complexities of quantifying dose rates are highlighted, and lessons learned are presented based on research with wild boar and snakes at Fukushima, wolves at Chornobyl, and reindeer in Norway. GPS-coupled dosimeters produced empirical data to which numerical simulations of external dose using computer software were compared. Our data did not support a standing paradigm in risk analyses: Using averaged soil contaminant levels to model external dose rates conservatively overestimate the dose to individuals within a population. Following this paradigm will likely lead to misguided recommendations for risk management. The GPS-dosimetry data also demonstrated the critical importance of how modeled external dose rates are impacted by the scale at which contaminants are mapped. When contaminant mapping scales are coarse even detailed knowledge about each animal's home range was inadequate to accurately predict external dose rates. Importantly, modeled external dose rates based on a single measurement at a trap site did not correlate to actual dose rates measured on free ranging animals. These findings provide empirical data to support published concerns about inadequate dosimetry in much of the published Chernobyl and Fukushima dose-effects research. Our data indicate that a huge portion of that literature should be challenged, and that improper dosimetry remains a significant source of controversy in radiation dose-effect research.

Variation in metal tolerance associated with population exposure history in Southern toads (Anaxyrus terrestris).

Human activities have radically shaped the global landscape, affecting the structure and function of ecosystems. Habitat loss is one of the most visible changes to the landscape and a primary driver of species declines; however, anthropogenic environmental contamination also threatens population persistence, but is not as readily observed. Aquatic organisms are especially susceptible to chemical perturbations, which can negatively impact survival and fitness related traits. Some populations have evolved tolerance to chemical stressors, which could mitigate the consequences associated with contamination. Amphibians are experiencing global declines due to multiple stressors and are particularly at risk to aquatic chemical stressors due to their permeable skin and reliance on wetlands for reproduction and larval development. However, amphibians also have substantial plasticity in response to environmental variation. We designed our study to examine whether tolerance to heavy metals is greater in Southern toad (Anaxyrus terrestris) larvae from wetlands with a history of contamination. Considering many of the most common trace elements elicit acute toxicity by disrupting osmotic- and ionic-regulation, we hypothesized that alterations to these aspects of physiology resulting from multigenerational exposure to trace element mixtures would be the most likely routes by which tolerance would evolve. We used copper (Cu) as a proxy for heavy metal exposure because it is a widely distributed aquatic stressor known to cause osmotic stress that can also cause mortality at levels commonly encountered in the environment. We found considerable within and among population variation in Cu tolerance, as measured by time to death. Larvae from populations living in sites contaminated with mixtures of heavy metals associated with coal fly ash were no more tolerant to Cu than those from reference sites. However, larvae from a population inhabiting a constructed wetland complex with high Cu levels were significantly more tolerant; having half the risk of mortality as reference animals. This wetland complex was created < 20 years ago, thus if elevated Cu tolerance in this population is due to selection in the aquatic habitat, such adaptation may occur rapidly (i.e. ∼10 generation). Our results provide evidence that amphibians may be able to evolve tolerance in response to trace element contamination, though such tolerance may be specific to the combination of contaminants present.

GPS-coupled contaminant monitors on free-ranging Chernobyl wolves challenge a fundamental assumption in exposure assessments.

Measurements of external contaminant exposures on individual wildlife are rare because of difficulties in using contaminant monitors on free-ranging animals. Most wildlife contaminant exposure data are therefore simulated with computer models. Rarely are empirical exposure data available to verify model simulations, or to test fundamental assumptions inherent in exposure assessments. We used GPS-coupled contaminant monitors to quantify external exposures to individual wolves (Canis lupus) living within the Belarus portion of Chernobyl's 30-km exclusion zone. The study provided data on animal location and contaminant exposure every 35 min for 6 months, resulting in ~6600 individual locations and 137Cs external exposure readings per wolf, representing the most robust external exposure data published to date on free ranging animals. The data provided information on variation in external exposure for each animal over time, as well as variation in external exposure among the eight wolves across the landscape of Chernobyl. The exposure data were then used to test a fundamental assumption in screening-level risk assessments, espoused in guidance documents of the U.S. Environmental Protection Agency and U.S. Department of Energy, - Mean contaminant concentrations conservatively estimate individual external exposures. We tested this assumption by comparing our empirical data to a series of simulations using the ERICA modeling tool. We found that modeled simulations of mean external exposure (10.5 mGy y-1), based on various measures of central tendency, under-predicted mean exposures measured on five of the eight wolves wearing GPS-contaminant monitors (i.e., 12.3, 26.3, 28.0, 28.8 and 35.7 mGy y-1). If under-prediction of exposure occurs for some animals, then arguably the use of averaged contaminant concentrations to predict external exposure is not as conservative as proposed by current risk assessment guidance. Thus, a risk assessor's interpretation of simulated exposures in a screening-level risk analysis might be misguided if contaminant concentrations are based on measures of central tendency. We offer three suggestions for risk assessors to consider in order to reduce the probability of underestimating exposure in a screening-level risk assessment.

Testing for associations between hematozoa infection and mercury in wading bird nestlings.

Several wading bird species in the southeastern US have a history of infection by hematozoa/avian malaria as well as mercury accumulation through their diet, and thus may be exposed to two, generally sublethal, yet chronic, stressors. We analyzed nestling wading birds (n = 171) of varying size and trophic position from the southeastern US, and a smaller sample (n = 23) of older, free-ranging birds, to look for potential interrelationships between infection by hematozoa and mercury (Hg) uptake. Only one nestling was PCR positive for hematozoa (Plasmodium/Haemoproteus) whereas nine (39%) of the older wading birds were positive. Sequencing indicated that both nestling and adult positives were infected with Plasmodium. Given the low infection rate of the nestlings, there was no association between Hg and malaria. The older birds exhibited a possible malaria/Hg association, but it may be confounded by their greater potential exposure period and large-scale movements.

32 species validation of a new Illumina paired-end approach for the development of microsatellites.

Development and optimization of novel species-specific microsatellites, or simple sequence repeats (SSRs) remains an important step for studies in ecology, evolution, and behavior. Numerous approaches exist for identifying new SSRs that vary widely in terms of both time and cost investments. A recent approach of using paired-end Illumina sequence data in conjunction with the bioinformatics pipeline, PAL_FINDER, has the potential to substantially reduce the cost and labor investment while also improving efficiency. However, it does not appear that the approach has been widely adopted, perhaps due to concerns over its broad applicability across taxa. Therefore, to validate the utility of the approach we developed SSRs for 32 species representing 30 families, 25 orders, 11 classes, and six phyla and optimized SSRs for 13 of the species. Overall the IPE method worked extremely well and we identified 1000s of SSRs for all species (mean = 128,485), with 17% of loci being potentially amplifiable loci, and 25% of these met our most stringent criteria designed to that avoid SSRs associated with repetitive elements. Approximately 61% of screened primers yielded strong amplification of a single locus.