Taricha Granulosa Research Articles

Feral frogs, native newts, and chemical cues: identifying threats from and management opportunities for invasive African Clawed Frogs in Washington state.

Invasive species threaten biodiversity globally. Amphibians are one of the most threatened vertebrate taxa and are particularly sensitive to invasive species, including other amphibians. African clawed frogs (Xenopus laevis) are native to Southern Africa but have subsequently become invasive on multiple continents-including multiple parts of North America-due to releases from the pet and biomedical trades. Despite their prevalence as a global invader, the impact of X. laevis remains understudied. This includes the Pacific Northwest of the USA, which now hosts multiple expanding X. laevis populations. For many amphibians, chemical cues communicate important information, including the presence of predators. Here, we tested the role chemical cues may play in mediating interactions between feral X. laevis and native amphibians in the Pacific Northwest. We tested whether native red-legged frog (Rana aurora) tadpoles display an antipredator response to non-native frog (X. laevis) or native newt (rough-skinned newts, Taricha granulosa) predator chemical stimuli. We found that R. aurora tadpoles exhibited pronounced anti-predator responses when exposed to chemical cues from T. granulosa but did not display anti-predator response to invasive X. laevis chemical cues. We also began experimentally testing whether T. granulosa-which produce a powerful neurotoxin tetrodotoxin (TTX)-may elicit an anti-predator response in X. laevis, that could serve to deter co-occupation. However, our short-duration experiments found that X. laevis were attracted to newt chemical stimuli rather than deterred. Our findings show that X. laevis likely poses a threat to native amphibians, and that these native species may also be particularly vulnerable to this invasive predator, compared to native predators, because toxic native newts may not limit X. laevis invasions. Our research provides some of the first indications that native Pacific Northwest species may be threatened by feral X. laevis and provides a foundation for future experiments testing potential management techniques for X. laevis.

Environmental DNA‐based detection of pathogens in trade and captive settings: Best practices and validation for Batrachochytrium salamandrivorans

Abstract Detecting pathogens in the live animal trade is critical for tracking and preventing their movement, introduction and spillover into susceptible fauna. However, the scale of the live animal trade makes individually testing animals infeasible for all but the most economically important taxa. For instance, while the fungal pathogen, Batrachochytrium salamandrivorans (Bsal), threatens amphibian, particularly caudate diversity, in Europe and the Americas, screening even a fraction of the millions of live amphibians imported into the United States, alone, is impractically laborious and expensive. A promising alternative to individual‐level sampling (e.g. swabbing the skin of salamanders) is to instead collect DNA from the animals' environment (e.g. housing container or water) which allows us to screen a whole group of animals at a time. We used a series of experiments with Bsal‐spiked water and substrates and experimentally infected rough‐skinned newts (Taricha granulosa) to determine which methods yield the most Bsal environmental DNA (eDNA) and evaluate the capacity of these methods to detect Bsal‐infected animals in conditions found in captive settings and trade. We found that filtering water housing infected animals for even an hour can consistently recover detectable levels of Bsal eDNA, that there is little evidence of Bsal eDNA being clumped in housing containers or swamped or inhibited by dirty housing containers, and that eDNA‐based methods achieves an equivalent or higher chance of detecting Bsal infections in a (virtual) population of co‐housed newts with fewer samples than individual swabs. By sampling the genetic materials accumulated from a whole group of animals, eDNA‐based methods are a powerful means of detecting pathogens, such as Bsal, in shipments and captive populations. These methods bring routine pathogen surveillance into reach in many more contexts and can thus be an important tool in conservation and disease control.

Phenotypic outcomes of predator–prey coevolution are predicted by landscape variation in climate and community composition

Abstract Landscape patterns of phenotypic coevolution are determined by variation in the outcome of predator–prey interactions. These outcomes may depend not only on the functional phenotypes that mediate species interactions, but also on aspects of the environment that enable encounters between coevolutionary partners. Exploring the relationship between coevolutionary traits and the environment requires extensive sampling across the range of the interaction to determine the relationship between local ecological variation and coevolution. In this study, we synthesized >30 years of data on predator–prey interactions between toxic newts (Taricha granulosa) and their snake predators (Thamnophis sirtalis) to explore the environmental predictors of arms race escalation. We found that geographic variation in phenotypes at the interface of coevolution was best predicted by a combination of community and climatic variation. Coevolutionary phenotypes were greatest in environments with climate favourable for newt–snake overlap. We found prey toxicity was elevated in regions with more predator species, and predator resistance was higher in regions with more prey species. Our results suggest specific environmental conditions reinforce the process of coevolution, signifying the phenotypic outcomes of coevolutionary arms races are sensitive to local ecological contexts that vary across the landscape. Read the free Plain Language Summary for this article on the Journal blog.

Aposematic coloration of Pacific newts (Taricha) provides a qualitatively but not quantitatively honest signal to predators

Abstract Colourful displays are used by diverse taxa to warn predators of dangerous defences (aposematism). Aposematic coloration is especially widespread among amphibians, which are often protected by harmful toxins. Pacific newts (Taricha) are considered a model of aposematism because when threatened, they arch the head and tail upwards to expose a vivid orange ventrum against a dark dorsum. Given that newts are defended by tetrodotoxin (TTX), a lethal neurotoxin, this signal is assumed to warn predators that an attack would be risky. However, colours have not been quantified in Taricha, and it remains unknown whether coloration provides qualitatively honest (signalling toxic defence) or quantitatively honest (signalling toxin level) warnings. We used two colour quantification methods (spectrometry and hyperspectral imaging) to measure chromatic (hue) and achromatic (brightness) qualities of ventral and dorsal coloration in two newt species (Taricha granulosa and Taricha sierrae). We assessed qualitative honesty using visual models of potential predators (snakes, birds and mammals). Next, we evaluated quantitative honesty by measuring TTX in newts and examining the potential correlation between defence level (amount of TTX) and colorimetrics. We found support for qualitative but not quantitative honesty. Selective pressures and evolutionary constraints might impede the evolution of honest quantitative signalling in this system.

Electrolyte imbalances and dehydration play a key role in Batrachochytrium salamandrivorans chytridiomycosis.

One of the most important emerging infectious diseases of amphibians is caused by the fungal pathogen Batrachochytrium salamandrivorans (Bsal). Bsal was recently discovered and is of global concern due to its potential to cause high mortality in amphibians, especially salamander species. To date, little has been reported on the pathophysiological effects of Bsal; however, studies of a similar fungus, B. dendrobatidis (Bd), have shown that electrolyte losses and immunosuppression likely play a key role in morbidity and mortality associated with this disease. The goal of this study was to investigate pathophysiological effects and immune responses associated with Bsal chytridiomycosis using 49 rough-skinned newts (Taricha granulosa) as the model species. Taricha granulosa were exposed to a 1 × 107 per 10 mL dose of Bsal zoospores and allowed to reach various stages of disease progression before being humanely euthanized. At the time of euthanasia, blood was collected for biochemical and hematological analyses as well as protein electrophoresis. Ten standardized body sections were histologically examined, and Bsal-induced skin lesions were counted and graded on a scale of 1-5 based on severity. Results indicated that electrolyte imbalances and dehydration induced by damage to the epidermis likely play a major role in the pathogenesis of Bsal chytridiomycosis in this species. Additionally, Bsal-infected, clinically diseased T. granulosa exhibited a systemic inflammatory response identified through alterations in complete blood counts and protein electrophoretograms. Overall, these results provide foundational information on the pathogenesis of this disease and highlight the differences and similarities between Bsal and Bd chytridiomycosis.

Vertebral anomalies in a natural population of Taricha granulosa (Caudata: Salamandridae)

Developmental plasticity, a common pattern in lissamphibian evolution, results in numerous alternative morphologies among species and also within populations. In the present study, a natural population of the salamander Taricha granulosa (Salamandridae) was examined to detect variation in the vertebral count and to identify potential deformities of their vertebral column. The number of trunk vertebrae varied between 11 and 13 and we recorded 58 individuals with 69 anomalous vertebral elements. These anomalies range from congenital malformations (block vertebrae, unilateral bars, hemivertebrae), extra ossifications in the haemal region, to posttraumatic pathologies. Most osseous pathologies were encountered in the caudal region of the axial skeleton. Our data suggest a high frequency of vertebral malformations in salamanders; however, the identification of the exact causes remains challenging.

Tetrodotoxin levels in lab-reared Rough-Skinned Newts (Taricha granulosa) after 3 years and comparison to wild-caught juveniles

The origin and biogenesis of tetrodotoxin (TTX) is one of the most interesting and perplexing questions remaining for TTX researchers. Newts can possess extreme quantities of TTX and are one of the most well-studied of all TTX-bearing organisms, yet seemingly conflicting results between studies on closely related species continues to generate debate. In this study, eggs from 12 female newts (Taricha granulosa) were reared in captivity and the metamorphosed juveniles were fed a TTX-free diet for 3 years. Using a non-lethal sampling technique, we collected skin samples from each individual each year. Wild-caught juveniles from the same population were also sampled for TTX. In lab-reared juveniles, mass increased rapidly, and after only 2 years individuals approached adult body mass. TTX levels increased slowly during the first two years and then jumped considerably in year three when fed a diet free of TTX. However, wild-caught juvenile newts of unknown age were more toxic than their lab-reared counterparts. These results, coupled with additional data on the long-term production and synthesis of TTX in adult newts suggest that TTX is unlikely to come through dietary acquisition, but rather newts may be able to synthesize their own toxin or acquire it from symbiotic bacteria.

A study on the genetic population structure and the tetrodotoxin content of rough-skinned newts, Taricha granulosa (Salamandridae), from their northern range of distribution

Rough-skinned newts, Taricha granulosa, which contain tetrodotoxin (TTX), a potent neurotoxin, are widely distributed along the west-coast of North America up to British Columbia (BC), Canada, and Southeast Alaska. Their genetic population structure using DNA-microsatellites and the TTX-content of specimens from British Columbia (Prince Rupert area) and Alaska (Revillagigedo Island, Shelter Island, and Juneau) were analysed. TTX-concentrations were low in newts from BC and Revillagigedo Island, but high in specimens from mainland Juneau, which had been deliberately introduced from Shelter Island, where TTX was not detectable in the individuals sampled. No significant genetic differences were detected between these populations, which may correlate with the high intraspecies variability of TTX. It is still an open question, which factors favour or induce the toxin production in the newts.

Identification of Tricyclic Guanidino Compounds from the Tetrodotoxin-Bearing Newt Taricha granulosa.

The biosynthesis of the potent neurotoxin tetrodotoxin (TTX, 1) is still unresolved. We used MS-guided screening and nuclear magnetic resonance analyses including long-range HSQMBC to characterize two novel skeletal tricyclic guanidino compounds, Tgr-288 (2a and 2b) and Tgr-210 (3), from the TTX-bearing newt, Taricha granulosa. The presence of these compounds in toxic newts is congruent with a previously proposed pathway for TTX biosynthesis in terrestrial organisms that includes a monoterpene precursor and the production of structurally diversified guanidino compounds.

Population dynamics and methodological assessments from a 15-year period of Amphibian monitoring in British Columbia's Southern Gulf Islands.

With amphibian populations facing a multitude of threats, including habitat loss, climate change, invasive species and infectious diseases, it is important to identify valuable amphibian habitat and the imminent pressures these environments face. Between 2004 and 2019, 6years of amphibian surveys were conducted at Greenburn, Roe and McLean lakes in the Southern Gulf Islands of British Columbia, Canada. We assessed (1) species composition and trends of native amphibians, including at-risk northern red-legged frog (Rana aurora); (2) observations of invasive American bullfrog (Lithobates catesbeianus); and (3) the efficacy of visual encounter and trapping survey methods in determining multi-species amphibian occupancy. The shallow, semi-ephemeral McLean Lake hosted more amphibian species and more breeding activity than the larger, deeper waters of Greenburn and Roe lakes. Despite multiple observations, bullfrogs have thus far not established a detectable population within these lakes, with the presence of native and introduced predators as potential contributing factors. Declining trends in occupancy of native populations of R. aurora, Pacific chorus frog (Pseudacris regilla) and rough-skinned newt (Taricha granulosa) were observed at all three lakes. Results varied within years by species and survey method, highlighting the importance of effective replication and employing complementary survey methods to optimize studies of amphibian occupancy. These observations also emphasize the value of shallow, small- to medium-sized waterbodies to native amphibian populations in the Southern Gulf Islands. As these waterbodies become increasingly threatened by global climate change and habitat degradation, the potential impacts of declining freshwater ecosystem health on amphibian populations should be considered.

Stable isotope analysis suggests that tetrodotoxin-resistant Common Gartersnakes (Thamnophis sirtalis) rarely feed on newts in the wild

Toxin-resistant predators may suffer costs from eating chemically defended prey and do not feed exclusively on toxic prey. Common Gartersnakes (Thamnophis sirtalis (Linnaeus, 1758)) have been considered the drivers of an evolutionary arms race with highly toxic newts (genus Taricha Gray, 1850), which they consume with few or no deleterious effects. However, how frequently newts are consumed in nature is less clear. To address this question, we investigated the diets of Th. sirtalis at a site in central Oregon where snakes have high levels of resistance and newts have high levels of tetrodotoxin in the skin. Because snake diets are difficult to quantify using traditional means, we used stable isotopes to estimate the proportion of Th. sirtalis diets made up of newts. Our estimate for the proportion of Th. sirtalis diet made up of Rough-skinned Newts (Taricha granulosa (Skilton, 1849)) at this site is 3.2%. Mole Salamanders (genus Ambystoma Tschudi, 1838) were predicted to be the most important prey, followed by slugs, chorus frogs, and mice, with a very minor role for earthworms. Our results demonstrate that even though Th. sirtalis are physiologically capable of consuming toxic prey, they do not often do so. Generalist predators can be exposed to very strong selection from, and exert reciprocal selection on even rarely eaten, chemically defended prey.

Beaver dams are associated with enhanced amphibian diversity via lengthened hydroperiods and increased representation of slow‐developing species

Abstract Land managers are increasingly using beavers to restore hydrological function, provide wildlife habitat, and mitigate the effects of climate extremes on water balances and ecosystems. Although North American beavers (Castor canadensis) and Eurasian beavers (Castor fiber) both hold great potential for landscape‐scale benefits, more information about the interactions between beavers and wildlife is necessary to maximise the ecological benefits and minimise the social and ecological costs of beaver‐centred management. Beaver dams create large, deep pools with long hydroperiods, which could benefit aquatic and semi‐aquatic species, especially pond‐breeding amphibians, which breed in still and slow‐moving water. We studied the relationship between beaver dams and pond‐breeding amphibians in the southern Washington Cascade Range of the north‐west U.S.A. by surveying 29 beaver‐dammed and 20 undammed lentic sites in three mid‐elevation (560–1,010 m) spatial blocks. We found that mean amphibian species richness was 2.7 times higher in dammed sites than in undammed sites (2.4 vs. 0.9 species). This increase in species richness was driven by increased occupancy of slow‐developing species—red‐legged frogs (Rana aurora) and northwestern salamanders (Ambystoma gracile)—which were also more abundant at sites with dams. These two species were detected almost exclusively in beaver‐dammed sites, suggesting that some amphibians rely heavily on beaver‐dammed sites for successful reproduction in areas such as our study blocks where ponds and wetlands with long hydroperiods are otherwise scarce. Species with highly variable development periods—long‐toed salamanders (Ambystoma macrodactylum) and rough‐skinned newts (Taricha granulosa)—showed nonsignificant trends of higher site occupancy and, in the case of newts, higher number of mating events per hectare in dammed sites compared to undammed sites. Compared to undammed sites, dammed ponds were consistently deeper and had longer hydroperiods, consistent with beavers benefitting slow‐developing amphibians primarily by increasing the quality of lentic breeding habitat. We suggest that slow‐developing amphibians and some variable‐rate developers might benefit greatly from beaver restoration, especially in areas where climate change is predicted to reduce summertime water levels. Beavers could therefore be useful and important components of ecosystem‐based restoration, management, and climate adaption, especially in parts of their native ranges in North America or Eurasia predicted to undergo climatic drying.

The geographic mosaic of arms race coevolution is closely matched to prey population structure.

Reciprocal adaptation is the hallmark of arms race coevolution. Local coadaptation between natural enemies should generate a geographic mosaic pattern where both species have roughly matched abilities across their shared range. However, mosaic variation in ecologically relevant traits can also arise from processes unrelated to reciprocal selection, such as population structure or local environmental conditions. We tested whether these alternative processes can account for trait variation in the geographic mosaic of arms race coevolution between resistant garter snakes (Thamnophis sirtalis) and toxic newts (Taricha granulosa). We found that predator resistance and prey toxin levels are functionally matched in co‐occurring populations, suggesting that mosaic variation in the armaments of both species results from the local pressures of reciprocal selection. By the same token, phenotypic and genetic variation in snake resistance deviates from neutral expectations of population genetic differentiation, showing a clear signature of adaptation to local toxin levels in newts. Contrastingly, newt toxin levels are best predicted by genetic differentiation among newt populations, and to a lesser extent, by the local environment and snake resistance. Exaggerated armaments suggest that coevolution occurs in certain hotspots, but prey population structure seems to be of particular influence on local phenotypic variation in both species throughout the geographic mosaic. Our results imply that processes other than reciprocal selection, like historical biogeography and environmental pressures, represent an important source of variation in the geographic mosaic of coevolution. Such a pattern supports the role of “trait remixing” in the geographic mosaic theory, the process by which non‐adaptive forces dictate spatial variation in the interactions among species.

A poisonous relationship

Toxins Many animal species harbor microbes that provide specialized services, such as the production of poisonous molecules that the animals can accumulate to protect them from predation. Vaelli et al. studied the skin microbiome of rough-skinned newts, which are known to have population-level variations in their propensity to accumulate the ion channel blocker tetrodotoxin (TTX). They found that newts with high levels of TTX harbored a very different set of bacterial species, including those capable of producing this toxin. They also identified three mutations within newt ion channels that confer TTX resistance in vitro. An important question raised by these results is whether newts can manipulate their microbiome to cultivate the bacteria that produce TTX. eLife 9 , e53898 (2020).

The geographic mosaic in parallel: Matching patterns of newt tetrodotoxin levels and snake resistance in multiple predator-prey pairs.

The Geographic Mosaic Theory of Coevolution predicts that coevolutionary arms races will vary over time and space because of the diverse ecological settings and population histories of interacting species across the landscape. Thus, understanding coevolution may require investigating broad sets of populations sampled across the range of the interaction. In addition, comparing coevolutionary dynamics between similar systems may reveal the importance of specific factors that structure coevolution. Here, we examine geographic patterns of prey traits and predator traits in the relatively unstudied interaction between the Sierra garter snake (Thamnophis couchii) and sympatric prey, the rough-skinned newt (Taricha granulosa), Sierra newt (Ta. sierrae) and California newt (Ta. torosa). This system parallels, in space and phenotypes, a classic example of coevolution between predatory common garter snakes (Th. sirtalis) and their toxic newt prey exhibiting hotspots of newt tetrodotoxin (TTX) levels and matching snake TTX resistance. We quantified prey and predator traits from hundreds of individuals across their distributions, and functional trait matching at sympatric sites. We show strong regional patterns of trait covariation across the shared ranges of Th. couchii and newt prey. Traits differ significantly among localities, with lower newt TTX levels and snake TTX resistance at the northern latitudes, and higher TTX levels and snake resistance at southern latitudes. Newts and snakes in northern populations show the highest degree of functional trait matching despite possessing the least extreme traits. Conversely, newts and snakes in southern populations show the greatest mismatch despite possessing exaggerated traits, with some snakes so resistant to TTX they would be unaffected by any sympatric newt. Nevertheless, individual variation was substantial, and appears to offer the opportunity for continued reciprocal selection in most populations. Overall, the three species of newts appear to be engaged in a TTX-mediated arms race with Th. couchii. These patterns are congruent with those seen between newts and Th. sirtalis, including the same latitudinal gradient in trait covariation, and the potential 'escape' from the arms race by snake predators. Such concordance in broad scale patterns across two distinct systems suggests common phenomena might structure geographic mosaics in similar ways.

The skin microbiome facilitates adaptive tetrodotoxin production in poisonous newts.

Rough-skinned newts (Taricha granulosa) use tetrodotoxin (TTX) to block voltage-gated sodium (Nav) channels as a chemical defense against predation. Interestingly, newts exhibit extreme population-level variation in toxicity attributed to a coevolutionary arms race with TTX-resistant predatory snakes, but the source of TTX in newts is unknown. Here, we investigated whether symbiotic bacteria isolated from toxic newts could produce TTX. We characterized the skin-associated microbiota from a toxic and non-toxic population of newts and established pure cultures of isolated bacterial symbionts from toxic newts. We then screened bacterial culture media for TTX using LC-MS/MS and identified TTX-producing bacterial strains from four genera, including Aeromonas, Pseudomonas, Shewanella, and Sphingopyxis. Additionally, we sequenced the Nav channel gene family in toxic newts and found that newts expressed Nav channels with modified TTX binding sites, conferring extreme physiological resistance to TTX. This study highlights the complex interactions among adaptive physiology, animal-bacterial symbiosis, and ecological context.

AMPHIBIAN MOVEMENT ACROSS A NEW RESIDENTIAL ROAD IN WESTERN WASHINGTON STATE

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

Variations in tetrodotoxin levels in populations of Taricha granulosa are expressed in the morphology of their cutaneous glands

Tetrodotoxin (TTX), one of the most toxic substances in nature, is present in bacteria, invertebrates, fishes, and amphibians. Marine organisms seem to bioaccumulate TTX from their food or acquire it from symbiotic bacteria, but its origin in amphibians is unclear. Taricha granulosa can exhibit high TTX levels, presumably concentrated in skin poison glands, acting as an agent of selection upon predatory garter snakes (Thamnophis). This co-evolutionary arms race induces variation in T. granulosa TTX levels, from very high to undetectable. Using morphology and biochemistry, we investigated differences in toxin localization and quality between two populations at the extremes of toxicity. TTX concentration within poison glands is related to the volume of a single cell type in which TTX occurs exclusively in distinctive secretory granules, suggesting a relationship between granule structure and chemical composition. TTX was detected in mucous glands in both populations, contradicting the general understanding that these glands do not secrete defensive chemicals and expanding currently held interpretations of amphibian skin gland functionality. Skin secretions of the two populations differed in low-mass molecules and proteins. Our results demonstrate that interpopulation variation in TTX levels is related to poison gland morphology.

Chance or choice? Understanding parasite selection and infection in multi-host communities

Ongoing debate over the relationship between biodiversity and disease risk underscores the need to develop a more mechanistic understanding of how changes in host community composition influence parasite transmission, particularly in complex communities with multiple hosts. A key challenge involves determining how motile parasites select among potential hosts and the degree to which this process shifts with community composition. Focusing on interactions between larval amphibians and the pathogenic trematode Ribeiroia ondatrae, we designed a novel, large-volume set of choice chambers to assess how the selectivity of free-swimming infectious parasites varied among five host species and in response to changes in assemblage composition (four different permutations). In a second set of trials, cercariae were allowed to contact and infect hosts, allowing comparison of host-parasite encounter rates (parasite choice) with infection outcomes (successful infections). Cercariae exhibited consistent preferences for specific host species that were independent of the community context; large-bodied amphibians, such as larval bullfrogs (Rana catesbeiana), exhibited the highest level of parasite attraction. However, because host attractiveness was decoupled from susceptibility to infection, assemblage composition sharply affected both per-host infection as well as total infection (summed among co-occurring hosts). Species such as the non-native R. catesbeiana functioned as epidemiological ‘sinks’ or dilution hosts, attracting a disproportionate fraction of parasites relative to the number that established successfully, whereas Taricha granulosa and especially Pseudacris regilla supported comparatively more metacercariae relative to cercariae selection. These findings provide a framework for integrating information on parasite preference in combination with more traditional factors such as host competence and density to forecast how changes within complex communities will affect parasite transmission.

Rough-skinned newt (Taricha granulosa) predation by Barred Owls (Strix varia)

ABSTRACT Barred Owls (Strix varia) are generalist predators that take a variety of birds, small mammals, herps, fish, crustaceans, insects, gastropods, and other invertebrates as prey. Here we document 2 different Barred Owl individuals that ingested rough-skinned newts (Taricha granulosa) as prey in northern California. Few vertebrate predators are known to feed on newts of the genus Taricha because they carry a potent defensive neurotoxin (tetrodotoxin) lethal to most vertebrate predators. Our examples suggest that Barred Owls may prey on newts in some areas and that consuming newts is not always lethal to Barred Owls.