Hyla Regilla Research Articles

Effects of carbaryl on species interactions of the foothill yellow legged frog (Rana boylii) and the Pacific treefrog (Pseudacris regilla)

Amphibian species worldwide are being confronted with novel anthropogenic stressors such as contaminants and invasive species. While much work has been done to examine these factors individually, less is known about how these stressors might interact. No studies to this point have examined the potentially synergistic impacts between these two stressors on a threatened amphibian species. We present the results from three separate laboratory studies focusing on two species of frogs, the Pacific tree frog (Pseudacris regilla) and a federal species of concern, the foothill yellow legged frog (Rana boylii). These experiments examine the toxicity of an insecticide, carbaryl, on each species, on their competitive interactions, and on their interaction with a non-native crayfish predator (Pacifastacus leniusculus). R. boylii were more susceptible to pesticide exposure than P. regilla and exposure reduced their ability to compete. This differential effect of the pesticide resulted in a remarkable increase in mortality (50%) for R. boylii with an invasive crayfish predator present while P. regilla exhibited no change. These results add to concerns over the utility of single species toxicity tests in determining safe levels for environmental exposure and advocate for the use of multiple species tests that focus on key species interactions.

In situ effects of pesticides on amphibians in the Sierra Nevada.

For more than 20years, conservationists have agreed that amphibian populations around the world are declining. Results obtained through laboratory or mesocosm studies and measurement of contaminant concentrations in areas experiencing declines have supported a role of contaminants in these declines. The current study examines the effects of contaminant exposure to amphibians in situ in areas actually experiencing declines. Early larval Pseudacris regilla were translocated among Lassen Volcanic, Yosemite and Sequoia National Parks, California, USA and caged in wetlands in 2001 and 2002 until metamorphosis. Twenty contaminants were identified in tadpoles with an average of 1.3-5.9 (maximum=10) contaminants per animal. Sequoia National Park, which had the greatest variety and concentrations of contaminants in 2001, also had tadpoles that experienced the greatest mortality, slowest developmental rates and lowest cholinesterase activities. Yosemite and Sequoia tadpoles and metamorphs had greater genotoxicity than those in Lassen during 2001, as determined by flow cytometry. In 2001 tadpoles at Yosemite had a significantly higher rate of malformations, characterized as hemimelia (shortened femurs), than those at the other two parks but no significant differences were observed in 2002. Fewer differences in contaminant types and concentrations existed among parks during 2002 compared to 2001. In 2002 Sequoia tadpoles had higher mortality and slower developmental rates but there was no difference among parks in cholinesterase activities. Although concentrations of most contaminants were below known lethal concentrations, simultaneous exposure to multiple chemicals and other stressors may have resulted in lethal and sublethal effects.

The effects of road noise on the calling behavior of Pacific chorus frogs

Fitness consequences of anthropogenic noise on organisms that have chorus-dependent breeding requirements, such as frogs, are not well understood. While frogs were thought to have innate and fixed call structure, species-specific vocal plasticity has been observed in populations experiencing high noise conditions. Adjustment to call structure, however, can have negative fitness implications in terms of energy expenditure and female choice. The Pacific chorus frog (Pseudacris regilla), a common vocal species broadly distributed throughout the Pacific Northwest, often breeds in waters impacted by road noise. We compared Pacific chorus frog call structure from breeding populations at 11 high- and low-traffic sites in the Willamette Valley, Oregon. We used passive acoustic monitoring and directional recordings to determine mean dominant frequency, amplitude, and call rate of breeding populations, individual frogs, and to quantify ambient road noise levels. Preliminary results indicate that while individuals do not differ in call rate or structure across noisy and quiet sites, high road noise levels decrease the effective communication distance of both the chorus and the individual. This research enhances our understanding of acoustic habitat in the Willamette Valley and the impacts of anthropogenic noise on a native amphibian species.

The effects of the amphibian chytrid fungus, insecticide exposure, and temperature on larval anuran development and survival.

Chytridiomycosis, a disease caused by Batrachochytrium dendrobatidis (Bd), has been implicated as a cause of amphibian declines. Susceptibility may be influenced by environmental factors that suppress the immune response. The authors conducted a laboratory study to examine the effect of temperature, insecticide exposure, and Bd exposure during larval anuran development. The authors examined the consequences of exposure to Bd, an insecticide (carbaryl or malathion), and static or fluctuating temperature (15 °C, 20 °C, 25 °C, or 15 °C to 25 °C 72-h flux) on larval development through metamorphosis of the Pacific treefrog (Pseudacris regilla). High and fluctuating temperature had negative effects on survival in the presence of Bd. Insecticides inhibited the effects of Bd; time to tail resorption of Pacific treefrogs decreased when tadpoles were exposed to carbaryl. The present study indicates that abiotic factors may play a role in the host-pathogen interactions in this system.

Combined influence of hydroperiod and parasitism on larval amphibian development

AbstractHydroperiod strongly influences the breeding period and development time of many amphibians, and larvae of various species display developmental plasticity in response to habitat drying. Hydrologic alterations associated with anthropogenic activities potentially can influence host–parasite interactions in humans and wildlife, but few investigators have examined this possibility. Pathogens can delay amphibian development, so infections could constrain the ability of parasitized larvae to respond to a shortened hydroperiod under drying conditions. We examined the individual and joint effects of hydroperiod and infection with a pathogenic trematode parasite (Ribeiroia ondatrae) on larval development of Pacific chorus frogs (Pseudacris regilla) in mesocosms. Tadpoles subjected to accelerated drying were twice as likely to emerge early. However, this tendency was most pronounced among uninfected individuals (96% of early-emerging individuals) and may have arisen from differences in competitive ability ...

Joint toxicity of chlorpyrifos and endosulfan to Pacific treefrog (Pseudacris regilla) tadpoles.

Recent ecotoxicology studies have focused on the potential interaction of pesticides and the effects these interactions may have on aquatic ecosystems. We examined the combined effects of two insecticides, endosulfan and chlorpyrifos, that have been previously examined individually on survival, growth, and development of Pacific treefrog (Pseudacris regilla) tadpoles. Historically, both pesticides have been heavily used in the Central Valley of California, been identified in downwind montane areas, and are highly toxic to amphibian larvae. Tadpoles were exposed to chlorpyrifos and endosulfan individually and in combination from Gosner stage 25 through metamorphosis to evaluate the individual effects and the interaction between these insecticides. Chlorpyrifos alone did not affect survival or body size after 30days, even at concentrations greater than the previously reported LC50. Survival and body size decreased with increasing endosulfan concentrations. The interactive effects of the insecticides depended on concentration and exposure duration. In combination, 137µg/L chlorpyrifos inhibited the negative effects of endosulfan on growth and survival. The presence of both insecticides in combination facilitated the development of axial malformations. In the presence of endosulfan with either 266 or 394µg/L chlorpyrifos, malformations occurred in 33 and 87% of tadpoles, respectively. Our results indicate that organophosphorus and organochlorine pesticides with different modes of action can result in varying interactions depending on their concentrations and on the end points being assessed. Further examination of contaminant impacts on natural aquatic systems should continue to focus on the effects of multiple contaminants and their potential for unpredictable, nonadditive interactions.

Climate warming mediates negative impacts of rapid pond drying for three amphibian species.

Anthropogenic climate change will present both opportunities and challenges for pool-breeding amphibians. Increased water temperature and accelerated drying may directly affect larval growth, development, and survival, yet the combined effects of these processes on larvae with future climate change remain poorly understood. Increased surface temperatures are projected to warm water and decrease water inputs, leading to earlier and faster wetland drying. So it is often assumed that larvae will experience negative synergistic impacts with combined warming and drying. However, an alternative hypothesis is that warming-induced increases in metabolic rate and aquatic resource availability might compensate for faster drying rates, generating antagonistic larval responses. We conducted a mesocosm experiment to test the individual and interactive effects of pool permanency (permanent vs. temporary) and water temperature (ambient vs. (+) -3 degrees C) on three anurans with fast-to-slow larval development rates (Great Basin spadefoot [Spea intermontana], Pacific chorus frog [Pseudacris regilla], and northern red-legged frog [Rana aurora]). We found that although tadpoles in warmed pools reached metamorphosis 15-17 days earlier, they did so with little cost (< 2 mm) to size, likely due to greater periphyton growth in warmed pools easing drying-induced resource competition. Warming and drying combined to act antagonistically on early growth (P = 0.06) and survival (P = 0.06), meaning the combined impact was less than the sum of the individual impacts. Warming and drying acted additively on time to and size at metamorphosis. These nonsynergistic impacts may result from cotolerance of larvae to warming and drying, as well as warming helping to offset negative impacts of drying. Our results indicate that combined pool warming and drying may not always be harmful for larval amphibians. However, they also demonstrate that antagonistic responses are difficult to predict, which poses a challenge to proactive conservation and management. Our study highlights the importance of considering the nature of multiple stressor interactions as amphibians are exposed to an increasing number of anthropogenic threats.

Heterogeneous hosts: how variation in host size, behaviour and immunity affects parasite aggregation

Infection heterogeneity is one of the most fundamental patterns in disease ecology, yet surprisingly few studies have experimentally explored its underlying drivers. Here, we used large-scale field assessments to evaluate the degree of parasite aggregation within amphibian host populations followed by a novel experimental approach to assess the potential influence of host size, behaviour and immunity in reproducing such heterogeneity. Among 227 wetlands, 2468 hosts and seven parasite species, infections were consistently aggregated among host individuals within populations of the Pacific chorus frog (Pseudacris regilla). For each parasite species, the relationship between the log-mean and log-variance of infection load was strongly linear (R(2): 0·91-0·98) with a slope between 1·37 and 1·67, indicative of aggregation relative to the expected Poisson slope of unity. In laboratory trials with P.regilla and the most virulent trematode (Ribeiroia ondatrae), experimental reductions in either host immunity (through corticosterone exposure) or antiparasite behaviours (through anaesthesia exposure) increased parasite infection loads in isolated hosts by 62-102% relative to unmanipulated individuals. In a second experiment designed to test how variation in host immunity, behaviour and body size affected variation in infection load within small groups (dyads), a reduction in immune function or behaviour of one host significantly amplified infection heterogeneity within the group, effectively doubling the variance-to-mean ratio. However, immunity affected aggregation only in the absence of behavioural manipulation, and changing the size distribution of hosts did not appreciably affect aggregation. Using Taylor's Power Law to integrate field and laboratory data, we found that only treatments involving behavioural reductions achieved aggregation levels comparable to natural host populations. Thus, despite their short duration, our treatments generated heterogeneity in infection loads similar to natural observations. These results emphasize how, alongside extrinsic variation in parasite exposure risk, individual host attributes generally and behaviour in particular have the potential to influence infection success and parasite aggregation. Continued integration of infection heterogeneity research across space, among host species, and over time has important implications for understanding and managing human and wildlife diseases.

Comparing the Status of Two Sympatric Amphibians in the Sierra Nevada, California: Insights on Ecological Risk and Monitoring Common Species

Abstract Basic information on species distribution and abundance is often lacking, even for common species. The historically abundant Mountain Yellow-legged (Rana sp.) and Pacific Treefrog (Pseudacris sp.) species complexes occur sympatrically and are exposed to similar threats. We evaluated the status of these species complexes on national forest lands in the Sierra Nevada, California as part of a long-term bioregional amphibian monitoring program. To determine occupancy and abundance indices, we surveyed all lentic and a sample of lotic habitats in 208 small watersheds (2–4 km2) selected using an unequal probability design where watersheds occupied previously had a higher likelihood of being selected. For Rana sp., results corroborated other assessments that the taxon has declined substantially. We found breeding activity in an estimated 0.04 (SE = 0.01) of watersheds rangewide, 0.47 (SE = 0.04) of watersheds with locality data from 1990–2001, and 0.02 (SE = 0.03) of watersheds with locality data prior ...

Predation and disease: understanding the effects of predators at several trophic levels on pathogen transmission

Summary Predators can directly and indirectly influence host–parasite interactions by consuming infected individuals, by removing infectious parasite stages and by changing host traits (e.g. behaviour). Because such effects can affect infection positively or negatively, understanding the net effects of predation on pathogen transmission under natural conditions is important. We conducted a mesocosm experiment to examine the effects of predators on interactions between tadpole hosts (Pseudacris regilla) and trematode parasites (Ribeiroia ondatrae). We manipulated the presence of (non‐lethal, i.e., caged) predators of tadpoles (dragonfly larvae) and (potentially lethal) parasite predators (damselfly larvae) to evaluate their individual and combined effects on host infection. We expected that dragonflies would reduce tadpole activity and thereby increase parasite infection through a reduction in antiparasite behaviour. Because damselflies can consume parasites in the laboratory, we predicted that damselflies would lower infection by consuming parasites before they infected tadpoles. Our goal was to evaluate the net consequences of these predator‐mediated effects for host/prey infection. The presence of caged dragonflies reduced tadpole activity, resulting in a ˜50% increase in average infection load compared to treatments without predators. In contrast to our prediction that damselflies would reduce infection, damselflies elicited behavioural and morphological changes in hosts similar to dragonflies, with a comparable increase in parasite transmission. Thus, predator‐mediated effects were evident predominantly through changes in host/prey behaviour, rather than through changes in the abundance of parasites. The lack of a direct effect of predators on infection (i.e. via consumption of parasites) could be the result of the presence of alternative prey (zooplankton) or a mismatch in timing between visual predators feeding during the day and parasites released from the first intermediate host and infecting amphibians at night. The presence of predators also stimulated morphological defences in their tadpole prey, including increased tail and body depth. Interestingly, we found that parasite infection also induced morphological changes in tadpole tail and body depth, similar to changes produced by (non‐lethal) cues from predators. Parasites caused malformations in tadpoles, but there were no effects on tadpole growth or development from either parasites or predators. This research has key implications for linking predation and infectious disease in aquatic ecosystems. Our results emphasise the importance of indirect effects of predators on infection and highlight possible trade‐offs in mitigating the concurrent risks of predation and disease. Parasites can also alter host morphology through trait‐mediated effects similar to predators, supporting a broader inclusion of parasites in the study of the ecology of natural enemies.

Thermal physiology and species distribution models reveal climate vulnerability of temperate amphibians

AbstractAimHigh‐latitude ectotherms are predicted to be less physiologically vulnerable to climate warming than tropical species based on their larger thermal safety margins, the distance between ambient temperatures and species' thermal optima. We sought to test the prediction that high latitude amphibians are buffered against the impacts of climate warming.LocationBritish Columbia, Canada.MethodsWe estimated the risk from climate change for three high‐latitude amphibian species (Spea intermontana, Rana aurora and Pseudacris regilla) by combining thermal performance experiments with species distribution models and predicted changes in maximum summer temperatures through the 2080s, in order to demonstrate temporal and geographical trends in vulnerability to climate warming among and within species.ResultsWe found that species have thermal safety margins of 3.2–3.8 °C based on current maximum summer temperatures. However, by the 2080s (emissions scenario A1B), we estimate that 45–82% of our focal species' current distributions will experience maximum summer temperatures above their thermal optima. We also found that by using long‐term average temperatures, as some studies have done, there were almost no scenarios in which populations of any species were experiencing temperatures greater than their thermal optima.Main conclusionsCombining spatially explicit species distribution models with performance physiology allows us to predict where limiting temperatures will occur in the coming decades, and can guide climate mitigation and conservation efforts before populations decline. Despite moderate thermal safety margins, high‐latitude ectotherms can be highly vulnerable to climate warming when spatio‐temporal variation is incorporated into estimates of risk as a result of climate change.

Temporal patterns in immunity, infection load and disease susceptibility: understanding the drivers of host responses in the amphibian‐chytrid fungus system

Summary Many pathogens infect a wide range of host species. However, variation in the outcome of infection often exists amongst hosts and is shaped by intrinsic host traits. For example, contact with pathogens may trigger changes in hosts directed toward preventing, fighting, or tolerating infection. Host responses to infection are dynamic; they change over time and vary depending on health, condition and within the context of the environment. Immunological defences are an important class of responses that mediate host–pathogen dynamics. Here, we examined temporal patterns of immunity in two amphibian species, Pacific tree frogs (Pseudacris regilla) and Cascades frogs (Rana cascadae), exposed to control conditions or experimental inoculation with the emerging infectious fungal pathogen, Batrachochytrium dendrobatidis (Bd). For each species, we compared bacterial killing ability of blood and differential white blood cell counts at four different time‐points after pathogen inoculation. We also quantified infection load over time and monitored survival. We detected qualitative and quantitative differences in species responses to Bd. Pseudacris regilla exhibited an increase in infection load over time and 16% of Bd‐exposed animals died during the experiment. Tree frogs lacked robust treatment differences in immune responses, but Bd‐exposed P. regilla tended to display weaker bacterial killing responses than unexposed control animals. Neutrophil counts did not vary consistently with treatment and lymphocytes tended to be less abundant in Bd‐exposed animals at the later sampling time‐points. In contrast, Bd‐exposed R. cascadae exhibited a decrease in infection load over time and no mortality occurred in the Bd treatment. Bd‐exposed Cascades frogs showed stronger bacterial killing responses and an elevated number of neutrophils in blood when compared with control animals, and both responses were upregulated within 48 h of pathogen exposure. Lymphocyte counts did not vary significantly with treatment. Although only statistically significant in Cascades frogs, neutrophil:lymphocyte ratios showed a trend of being elevated in Bd‐exposed animals of both species and are indicative of pathogen‐induced physiological stress. Our results suggest that variation in systemic immunological responses of two syntopic amphibian species is associated with and may contribute to differential patterns of survival and infection load during exposure to the chytrid fungus. Species variation in immunological responses as soon as 48 h after pathogen exposure suggests that initial host–pathogen interactions may set the stage for subsequent infection and disease progression. Variation in host responses can drive disease dynamics and comparative studies of host responses to pathogens are critical for making predictions about pathogen emergence, spread and persistence.

Acoustic monitoring of breeding amphibians at Yosemite National Park and Point Reyes National Seashore

The calling behavior of frogs and toads at breeding sites lends itself to acoustic monitoring of these amphibian populations. We are using Automated Recording Devices (ARD) at two National Park units in California, Yosemite National Park and Point Reyes National Seashore, to monitor the breeding efforts of amphibians by recording their calls. We are monitoring both common species (Pacific chorus frogs, Pseudacris regilla, occurs in both parks) and imperiled species (Yosemite toad, Anaxyrus canorus, Yosemite; California red-legged frog, Rana draytonii, Point Reyes) to investigate whether breeding phenology will shift with changing climatic conditions. The use of ARD is also providing a more complete picture of the diel calling patterns of these species, and how some species are partitioning their acoustical environment by frequency and time in order to breed successfully while surrounded by noisy neighbors. Information gathered through acoustic monitoring is very valuable for conserving rare amphibians and ensuring that common species remain common.

The amphibian skin‐associated microbiome across species, space and life history stages

Skin-associated bacteria of amphibians are increasingly recognized for their role in defence against pathogens, yet we have little understanding of their basic ecology. Here, we use high-throughput 16S rRNA gene sequencing to examine the host and environmental influences on the skin microbiota of the cohabiting amphibian species Anaxyrus boreas, Pseudacris regilla, Taricha torosa and Lithobates catesbeianus from the Central Valley in California. We also studied populations of Rana cascadae over a large geographic range in the Klamath Mountain range of Northern California, and across developmental stages within a single site. Dominant bacterial phylotypes on amphibian skin included taxa from Bacteroidetes, Gammaproteobacteria, Alphaproteobacteria, Firmicutes, Sphingobacteria and Actinobacteria. Amphibian species identity was the strongest predictor of microbial community composition. Secondarily, within a given amphibian species, wetland site explained significant variation. Amphibian-associated microbiota differed systematically from microbial assemblages in their environments. Rana cascadae tadpoles have skin bacterial communities distinct from postmetamorphic conspecifics, indicating a strong developmental shift in the skin microbes following metamorphosis. Establishing patterns observed in the skin microbiota of wild amphibians and environmental factors that underlie them is necessary to understand skin symbiont community assembly, and ultimately, the role skin microbiota play in the extended host phenotype including disease resistance.

Variations in lethal and sublethal effects of cypermethrin among aquatic stages and species of anuran amphibians

Despite the use of model species to predict the effects of chemicals in the environment, unpredicted variation in levels of risk to organisms from xenobiotics can be observed. Physiological and morphological differences between species and life stages may lead to differences in sensitivity, while seasonal and spatial variation in pesticide concentrations may affect the level of risk faced by organisms in the environment. Because anurans breed in aquatic habitats subject to contamination by runoff and spraying, they are particularly vulnerable to pesticides. In the present study, embryos, newly hatched larvae, and larvae with limb buds of 3 anuran amphibian species--Pseudacris regilla, Rana cascadae, and Rana aurora--were exposed for 48 h to either 0.5 µg/L or 5.0 µg/L cypermethrin under laboratory conditions. The authors monitored hatching success, larval survival, and measured growth. Additionally, they assayed avoidance behavior 2 wk after exposure or 2 wk after hatching for individuals exposed as embryos. Hatching and survival were not affected in animals of any species exposed as embryos. After exposure as embryos and as newly hatched larvae, however, P. regilla displayed behavioral abnormalities in response to prodding. Cypermethrin increased mortality in P. regilla exposed in both larval stages. Cypermethrin also increased mortality in larval R. cascadae when exposed at the early stage. These results indicate variation in sensitivity to environmentally relevant concentrations of cypermethrin among anuran species and life stages.

Transcriptome resources for the frogs Lithobates clamitans and Pseudacris regilla, emphasizing antimicrobial peptides and conserved loci for phylogenetics

We developed genetic resources for two North American frogs, Lithobates clamitans and Pseudacris regilla, widespread native amphibians that are potential indicator species of environmental health. For both species, mRNA from multiple tissues was sequenced using 454 technology. De novo assemblies with Mira3 resulted in 50238 contigs (N50=687bp) and 48213 contigs (N50=686bp) for L.clamitans and P.regilla, respectively, after clustering with CD-Hit-EST and purging contigs below 200bp. We performed BLASTX similarity searches against the Xenopus tropicalis proteome and, for predicted ORFs, HMMER similarity searches against the Pfam-A database. Because there is broad interest in amphibian immune factors, we manually annotated putative antimicrobial peptides. To identify conserved regions suitable for amplicon resequencing across a broad taxonomic range, we performed an additional assembly of public short-read transcriptome data derived from two species of the genus Rana and identified reciprocal best TBLASTX matches among all assemblies. Although P.regilla, a hylid frog, is substantially more diverged from the ranid species, we identified 56 genes that were sufficiently conserved to allow nondegenerate primer design with Primer3. In addition to providing a foundation for comparative genomics and quantitative gene expression analysis, our results enable quick development of nuclear sequence-based markers for phylogenetics or population genetics.

Divergent responses of exposed and naive Pacific tree frog tadpoles to invasive predatory crayfish

Invasive predators can devastate native species and ecosystems. However, native species may be able to coexist with invasive predators through a variety of mechanisms, such as changes in morphology or behavior due to a plastic response or selection on fixed anti-predator traits. We examined whether exposed and naive populations of Pacific tree frog tadpoles (Pseudacris regilla) display divergent morphological and behavioral traits in response to the invasive predatory red swamp crayfish (Procambarus clarkii). Tadpoles were collected from three study streams with and three without crayfish, in the Santa Monica Mountains of Southern California. We analyzed tadpole morphology and tested anti-predator behavior and survival in the laboratory. Tadpoles from streams with crayfish had shallower, narrower tails than tadpoles from streams without crayfish. Tadpoles from streams with and without crayfish were less active after exposure to crayfish chemical cues. The divergent morphology of naive and exposed tadpoles is consistent with tadpoles exhibiting a plastic response to crayfish or undergoing selection from crayfish predation. In laboratory predation experiments, we found no difference in survival between tadpoles from streams with and without crayfish but tadpoles that survived predation had deeper tail muscles than those that were killed or injured. Our results suggest that deeper tails are advantageous in the presence of crayfish, yet tadpoles from crayfish streams had shallower tails than those from crayfish-free streams. Shallower tails may have an alternative unmeasured advantage or there may be a physiological constraint to developing deeper tails in the wild. These results highlight the ability of a native frog to respond to an invasive predatory crayfish, potentially allowing for coexistence.

Accumulation of pesticides in pacific chorus frogs (Pseudacris regilla) from California's Sierra Nevada Mountains, USA

Pesticides are receiving increasing attention as potential causes of amphibian declines, acting singly or in combination with other stressors, but limited information is available on the accumulation of current-use pesticides in tissue. The authors examined potential exposure and accumulation of currently used pesticides in pond-breeding frogs (Pseudacris regilla) collected from 7 high elevations sites in northern California. All sites sampled are located downwind of California's highly agricultural Central Valley and receive inputs of pesticides through precipitation and/or dry deposition. Whole frog tissue, water, and sediment were analyzed for more than 90 current-use pesticides and pesticide degradates using gas chromatography-mass spectrometry. Two fungicides, pyraclostrobin and tebuconazole, and one herbicide, simazine, were the most frequently detected pesticides in tissue samples. Median pesticide concentration ranged from 13 µg/kg to 235 µg/kg wet weight. Tebuconazole and pyraclostrobin were the only 2 compounds observed frequently in frog tissue and sediment. Significant spatial differences in tissue concentration were observed, which corresponded to pesticide use in the upwind counties. Data generated indicated that amphibians residing in remote locations are exposed to and capable of accumulating current-use pesticides. A comparison of P. regilla tissue concentrations with water and sediment data indicated that the frogs are accumulating pesticides and are potentially a more reliable indicator of exposure to this group of pesticides than either water or sediment.

Does timing matter? How priority effects influence the outcome of parasite interactions within hosts

In nature, hosts are exposed to an assemblage of parasite species that collectively form a complex community within the host. To date, however, our understanding of how within-host-parasite communities assemble and interact remains limited. Using a larval amphibian host (Pacific chorus frog, Pseudacris regilla) and two common trematode parasites (Ribeiroia ondatrae and Echinostoma trivolvis), we experimentally examined how the sequence of host exposure influenced parasite interactions within hosts. While there was no evidence that the parasites interacted when hosts were exposed to both parasites simultaneously, we detected evidence of both intraspecific and interspecific competition when exposures were temporally staggered. However, the strength and outcome of these priority effects depended on the sequence of addition, even after accounting for the fact that parasites added early in host development were more likely to encyst compared to parasites added later. Ribeiroia infection success was reduced by 14 % when Echinostoma was added prior to Ribeiroia, whereas no such effect was noted for Echinostoma when Ribeiroia was added first. Using a novel fluorescent-labeling technique that allowed us to track Ribeiroia infections from different exposure events, we also discovered that, similar to the interspecific interactions, early encysting parasites reduced the encystment success of later arriving parasites by 41 %, which could be mediated by host immune responses and/or competition for space. These results suggest that parasite identity interacts with host immune responses to mediate parasite interactions within the host, such that priority effects may play an important role in structuring parasite communities within hosts. This knowledge can be used to assess host-parasite interactions within natural communities in which environmental conditions can lead to heterogeneity in the timing and composition of host exposure to parasites.

Winner and runners‐up of the 2012 best paper award

Environmental Toxicology and ChemistryVolume 32, Issue 7 p. 1437-1437 ET&C Best Paper of 2012Free Access Winner and runners-up of the 2012 best paper award First published: 04 June 2013 https://doi.org/10.1002/etc.2252AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Deposition and accumulation of airborne organic contaminants in Yosemite National Park, California M. Alisa Mast, David A. Alvarez, and Steven D. Zaugg DOI: 10.1002/etc.1727 Mast et al. 1 was cited by the review panel for excellence in experimental approach, scientific impact, and public and professional interest in protecting a national resource—Yosemite National Park (California, USA). The park lies upwind of intensive agricultural activity in the San Joaquin Valley (California, USA). Mast et al. 1 report the results of an intensive sampling campaign in Yosemite from 2008 to 2009 that documented the presence of both current-use and legacy pesticides in snow, lichens, zooplankton, passive samplers, and lake sediments from elevations ranging from approximately 1200 m to 3500 m. The study's rigorous quality assurance/quality control methods, provided in detail in the Supplemental Information, led the review panel to cite the study for its excellence in experimental approach. In addition, the authors clearly demonstrate the presence of pesticides that were identified by Sparling and Fellers 2 as having adverse effects in 2 frog species from the Sierras, larval Pacific treefrogs (Pseudacris regilla), and foothill yellow-legged frogs (Rana boylii). Their work contributes substantially to the understanding of spatial and temporal distributions of pesticides in the Sierra Nevada. Figure 1Open in figure viewerPowerPoint Image of Best Paper Award winner M. Alisa Mast. REFERENCES 1 Mast MA, Alvarez DA, Zaugg SD. 2012. Deposition and accumulation of airborne organic contaminants in Yosemite National Park, California. Environ Toxicol Chem 31: 524– 533. Wiley Online LibraryCASPubMedWeb of Science®Google Scholar 2 Sparling DW, Fellers GM. 2009. Toxicity of two insecticides to California, USA, anurans and its relevance to declining amphibian populations. Environ Toxicol Chem 28: 1696– 1703. Wiley Online LibraryCASPubMedWeb of Science®Google Scholar Cindy M. Lee Clemson University Anderson, South Carolina, USA FIRST RUNNER-UP: Influence of carbon and lipid sources on variation of mercury and other trace elements in polar bears (Ursus maritimus) Heli Routti, Robert J. Letcher, Erik W. Born, Marsha Branigan, Rune Dietz, Thomas J. Evans, Melissa A. McKinney, Elizabeth Peacock, and Christian Sonne DOI: 10.1002/etc.2005 SECOND RUNNER-UP (tie): Bridging environmental mixtures and toxic effects Sarah E. Allan, Brian W. Smith, Robert L Tanguay, and Kim A. Anderson DOI: 10.1002/etc.2018 SECOND RUNNER-UP (tie): Changes in benthic nutrient sources within a wetland after hydrologic reconnection James S. Kuwabara, Brent R. Topping, James L. Carter, Tamara M. Wood, Jason M. Cameron, Jessica R. Asbill-Case, and Rick A. Carlson DOI: 10.1002/etc.1914 THIRD RUNNER-UP (tie): Quantifying the anthropogenic fraction of fatty alcohols in a terrestrial environment Stephen M. Mudge, Paul C. DeLeo, and Scott D. Dyer DOI: 10.1002/etc.1808 THIRD RUNNER-UP (tie): Dissolved organic matter reduces algal accumulation of methylmercury Allison C. Luengen, Nicholas S. Fisher, and Brian A. Bergamaschi DOI: 10.1002/etc.1885 Volume32, Issue7July 2013Pages 1437-1437 FiguresReferencesRelatedInformation