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Classical theory suggests that parasites will exhibit higher fitness in sympatric relative to allopatric host populations (local adaptation). However, evidence for local adaptation in natural host-parasite systems is often equivocal, emphasizing the need for infection experiments conducted over realistic geographic scales and comparisons among species with varied life history traits. Here, we used infection experiments to test how two trematode (flatworm) species (Paralechriorchis syntomentera and Ribeiroia ondatrae) with differing dispersal abilities varied in the strength of local adaptation to their amphibian hosts. Both parasites have complex life cycles involving sequential transmission among aquatic snails, larval amphibians and vertebrate definitive hosts that control dispersal across the landscape. By experimentally pairing 26 host-by-parasite population infection combinations from across the western USA with analyses of host and parasite spatial genetic structure, we found that increasing geographic distance-and corresponding increases in host population genetic distance-reduced infection success for P. syntomentera, which is dispersed by snake definitive hosts. For the avian-dispersed R. ondatrae, in contrast, the geographic distance between the parasite and host populations had no influence on infection success. Differences in local adaptation corresponded to parasite genetic structure; although populations of P. syntomentera exhibited ~10% mtDNA sequence divergence, those of R. ondatrae were nearly identical (

In the spring and summer of 2020, we found cysts of the nematode Eustrongylides spp. in Brown Trout (Salmo trutta), Rainbow Trout (Oncorhynchus mykiss), and Mountain Whitefish (Prosopium williamsoni) in the Deschutes River. The prevalence and maximum intensity of infection exceeded the range of published accounts for Eustrongylides spp. across a wide range of species. Because the 1st intermediate host is likely to be a tubificid worm, also known as a sludge worm or sewage worm, this exceptional prevalence of Eustrongylides spp. infection raises questions about conditions in the river that may be contributing to the high infection rate in fish.

Published accounts describe the eggs of spotted frogs (Rana luteiventris and Rana pretiosa) as having either 1 or 2 jelly envelopes surrounding the ovum. Eggs of R. luteiventris are typically reported to have a single jelly envelope, whereas those of R. pretiosa are reported to have 2 envelopes. We found, however, that both species' eggs actually have 3 jelly envelopes. In this paper we describe the eggs of both species, and identify the origin of the discrepancy in the scientific literature.

Despite the important roles of freshwater gastropods in aquatic ecosystems, the taxonomic status of many taxa is unclear, which is compounded by a lack of information on species population genetic structuring, distribution, and dispersal patterns. The objective of this study was to address the biogeography of the freshwater snail Planorbella trivolvis (Gastropoda: Planorbidae) in the western United States. We amplified two genetic markers (16S, COI) from individuals belonging to western USA populations and downloaded genetic data from GenBank. We utilized minimum spanning networks to assess the genetic patterns and performed Analysis of Molecular Variance and linear regression analyses to determine how geographic distance and watershed identity contributed to the observed genetic structuring. For both markers, we found that the majority of genetic variation was associated within and among populations, rather than among watersheds. Correspondingly, there was no significant effect of geographic distance on genetic distance, suggesting that long-distance dispersal was promoting gene flow between populations. The genetic similarity could reflect avian-mediated dispersal of snails along the Pacific Flyway, a major waterfowl migratory corridor. Further analysis of the population structuring across North America revealed East-West genetic structuring, suggesting that across longitudinal gradients P. trivolvis experiences significant genetic isolation.

The Oregon Spotted Frog (Rana pretiosa) is endemic to the Pacific Northwest and was recently listed as threatened under the Endangered Species Act. We tested the hypothesis that reproductive or physiological stress and parasitic disease may be contributing to the decline of this species. We histologically examined gonads and kidneys of newly metamorphosed wild-caught R. pretiosa to confirm sex and search for evidence of abnormal reproductive development and parasites. A subset of these specimens were also cleared and stained for examination of their skeletal morphology to identify potential skeletal malformations. The sex ratio did not differ significantly from 1:1, and we found no skeletal abnormalities. Trematode metacercarial parasites were present in the kidneys of all Spotted Frogs examined. We also report, for the first time, oocytes developing in the testes of 5 out of the 11 newly metamorphosed male Spotted Frogs examined. Further study into gonadal development of this species is necessary to investigate the significance of testicular oocytes in developing R. pretiosa and to identify whether these gonadal abnormalities are related in any way to their decline.

Placobdella sophieae Oceguera-Figueroa et al., 2010 (Hirudinida: Glossiphoniidae) is reported from Oregon, California, and British Columbia for the first time. New hosts reported for P. sophieae include Taricha granulosa (rough- skinned newt), Rana pretiosa (Oregon spotted frog), and Anaxyrus boreas (western toad). Placobdella sophieae exhibits relatively low host specificity and all amphibians occurring in the Pacific Northwest are potential hosts.

Parasite infections often lead to dramatically different outcomes among host species. Although an emerging body of ecoimmunological research proposes that hosts experience a fundamental trade-off between pathogen defences and life-history activities, this line of inquiry has rarely been extended to the most essential outcomes of host-pathogen interactions: namely, infection and disease pathology. Using a comparative experimental approach involving 13 amphibian host species and a virulent parasite, we test the hypothesis that pace-of-life predicts parasite infection and host pathology. Trematode exposure increased mortality and malformations in nine host species. After accounting for evolutionary history, species that developed quickly and metamorphosed smaller (fast-species) were particularly prone to infection and pathology. This pattern likely resulted from both weaker host defences and greater adaptation by parasites to infect common hosts. Broader integration between life history theory and disease ecology can aid in identifying both reservoir hosts and species at risk of disease-driven declines.

Summary 1. An emerging framework in animal disease ecology seeks to ‘decompose’ a host’s response to disease into resistance, or its ability to resist infection following exposure, and tolerance, or its ability to limit the damage associated with infection. How these processes vary over the life history of a host, however, and whether developmental changes in resistance and tolerance account for ‘critical windows’ of disease vulnerability remain open questions. 2. Critical developmental windows are particularly important for infections that alter host development. Recently, increased observations of amphibians with severe limb malformations have stimulated debate over the causes responsible and whether malformation types can be used to infer the agent responsible. The trematode parasite Ribeiroia ondatrae, for example, is often implicated in accounts of extra-legged frogs, but is believed to be unimportant in explaining missing legged animals. Here, we test the influence of host developmental stage, from eggs to post-metamorphosis, on the risk of mortality and the types of malformations produced in Pacific chorus frogs (Pseudacris regilla) following exposure to trematode infection. 3. Consistent with a critical window of vulnerability, host mortality and malformations were greatest among animals exposed during pre-limb and early limb development (15–90%) and decreased to

minima, egg mass, oviposition More than half of the known remaining populations of the Oregon Spotted Frog (Rana pretiosa) are at elevations .1200 m along the Cascade Range and its eastern flank in Oregon (Pearl and Hayes 2005). Rana pretiosa in this region typically breed soon after thaw and often lay eggs in water ,20 cm deep (Pearl and others 2009). Egg masses in shallow microhabitats experience broad temperature fluctuations, and ice formation on the surface is common (Bull and Shepherd 2003). At .20 oviposition sites around Sunriver in central Oregon (elevation 1270 m), we have observed high survival of R. pretiosa embryos after exposure to subfreezing air temperatures and ice cover for up to several days. These observations and the characteristics of oviposition sites across much of the species’ range along the Cascade Range suggest that R. pretiosa eggs in this region may be more tolerant of low temperatures than previously reported. Information on thermal limits of R. pretiosa embryos derives from studies of 1 population in the Fraser River Valley of southwestern British Columbia. The low elevation of this site (approximately 50 m above sea level) and its proximity to the Strait of Georgia and Pacific Ocean make its climate more moderate than much of the extant range of R. pretiosa. Licht (1971) reported a lethal minimum, the temperature at which egg survival is ,50%, near 66C for eggs from that site at a range of stable temperature treatments in the laboratory. A subset of embryos survived lower temperatures for up to 8 h, after which trials were terminated (Licht 1971), but data were not presented on presence or timing of develop

Renewed controversy has emerged over the likely causes and consequences of deformed amphibians, particularly those with missing limbs. The results of a series of experiments by Ballengée and Sessions (2009) implicate aquatic predators (i.e. dragonfly larvae) in causing such abnormalities. Skelly and Benard (2010), however, argued that the small scale of these experiments and the absence of a correlation between predator abundance and deformity frequencies in natural amphibian populations undermine such a conclusion. Drawing upon our experiences with frog malformations, we suggest that the study of amphibian deformities has been hindered by two, interrelated problems. First, empirical studies often fail to critically define the expected baseline level of abnormalities and differentiate between "epidemic" and "endemic" frequencies of malformations. Second, recognizing the likelihood of multiple causes in driving amphibian malformations, continued research needs to embrace a "multiple lines of evidence" approach that allows for complex etiologies by integrating field surveys, diagnostic pathology, comparative modeling, and experiments across a range of ecological scales. We conclude by highlighting the results of a recent study that uses this approach to identify the role of aquatic predators (i.e., fishes and dragonflies) in causing high frequencies of deformed frogs in Oregon. By combining long-term data, comparative data and mechanistic experiments, this study provides compelling evidence that certain predators do cause deformities under ecologically relevant conditions. In light of continuing concerns about amphibian deformities and population declines, we emphasize the need to integrate ecological, epidemiological, and developmental tools in addressing such environmental enigmas.

While many predators completely consume their prey, others feed only on blood or tissue without killing the prey, sometimes causing ecologically significant levels of injury. We investigated the importance of sublethal predator attacks in driving an emerging issue of conservation importance: missing-limb deformities in amphibians. We combined long term field data and manipulative experiments to evaluate the role of sublethal predation in causing abnormalities in two regions of central Oregon, USA. Since 1988, western toads (Bufo boreas) in Lake Aspen have exhibited abnormalities dominated by partially missing limbs and digits at annual frequencies from < 1% to 35%. On Broken Top volcano, we found comparable types and frequencies of abnormalities in Cascades frogs (Rana cascadae). Field sampling and observational data implicated two aquatic predators in these abnormality phenomena: introduced sticklebacks (Gasterosteus aculeatus) at Lake Aspen and corduliid dragonfly larvae (Somatochlora albicinctd) at Broken Top. In experiments, these predators produced limb abnormalities identical to those observed in the respective regions. At Lake Aspen, in situ predator exclosures effectively eliminated abnormalities in toads, while comparisons among years with low and high stickleback abundance and between wetlands with and without sticklebacks reinforced the link between fish and amphibian abnormalities. Neither trematode parasite infection nor pesticide contamination could explain observed abnormalities. Our results suggest that predators are an important explanation for missing-limb abnormalities and highlight the ecological significance of sublethal predation in nature.

We used genetic methods to estimate the effective number of breeders (N b) in a population of Rana pretiosa, an imperiled amphibian in western North America. Microsatellite data was gathered from large samples of adults, eggs, and juveniles collected in 2006. We wished to determine where in the life cycle the greatest reductions in N b occur, and to compare genetic estimates of N b to an egg mass count estimate of the number of breeding adults. We predicted that N b estimated at the metamorph stage would be reduced by increased variance in family size due to egg mass mortality. Contrary to our prediction, estimates of N b at the egg and metamorph stages were similar. Thus, we found no evidence of inflated variance in family size between the two stages. If our results for this population are typical for R. pretiosa, then increased variance in family size during the egg to metamorph stage may not be a strong factor in reducing the effective population sizes (N e) relative to the census sizes (N) in this species.

We used five years of recapture data and Bayesian estimation to assess seasonal survival, movement, and growth of Oregon Spotted Frogs (Rana pretiosa) relocated into created ponds at Dilman Meadow in Oregon, USA. We evaluate hypotheses specific to the relocation and elucidate aspects of R. pretiosa life history that are poorly known. The odds of survival of relocated individuals during the first year following relocation were 0.36 times the survival odds of relocated and non-relocated frogs after one year since the relocation. Survival rate was higher for large frogs. After accounting for frog size, we found little variation in survival between ponds at Dilman Meadow. Survival was lowest for males during the breeding/post-breeding redistribution period, suggesting a high cost of breeding for males. The highest survival rates occurred during winter for both genders, and one small spring was used heavily during winter but was used rarely during the rest of the year. Individual growth was higher in ...

Chytridiomycosis (infection by the fungus Batrachochytrium dendrobatidis) has been associated with amphibian declines in at least four continents. We report results of disease screens from 210 pond-breeding amphibians from 37 field sites in Oregon and Washington. We detected B. dendrobatidis on 28% of sampled amphibians, and we found ≥ 1 detection of B. dendrobatidis from 43% of sites. Four of seven species tested positive for B. dendrobatidis, including the Northern Red-Legged Frog (Rana aurora), Columbia Spotted Frog (Rana luteiventris), and Oregon Spotted Frog (Rana pretiosa). We also detected B. dendrobatidis in nonnative American Bullfrogs (Rana catesbeiana) from six sites in western and central Oregon. Our study and other recently published findings suggest that B. dendrobatidis has few geographic and host taxa limitations among North American anurans. Further research on virulence, transmissibility, persistence, and interactions with other stressors is needed to assess the potential impact...

Introduced American bullfrogs (Rana catesbeiana) come in contact with native amphibians on four continents and are well established in lowlands of western North America. To date, research on the effects of introduced bullfrogs on native frogs has focused on competition and predation, and is based largely on larval interactions. We present observations of interspecific amplexus between bullfrogs and two native ranid frogs (R. aurora and R. pretiosa) from six sites across the Pacific Northwest that imply that this interaction is more widespread than currently recognized. Our observations indicate that R. catesbeiana juveniles and subadults in this region are of appropriate size to elicit marked amplectic responses from males of both native species. Our literature review suggests that greater opportunity may exist for pairings between R. catesbeiana and native R. aurora or R. pretiosa than among syntopic native ranids in western North America. We hypothesize that interspecific amplexus with introduc...

Parasites and pathogens can influence the survivorship, behavior, and very structure of their host species. For example, experimental studies have shown that trematode parasites can cause high frequencies of severe limb malformations in amphibians. In a broad-scale field survey covering parts of California, Oregon, Washington, Idaho, and Montana, we examined relationships between the frequency and types of morphological abnormalities in amphibians and the abundance of trematode parasite infection, pH, con- centrations of 61 pesticides, and levels of orthophosphate and total nitrate. We recorded severe malformations at frequencies ranging from 1% to 90% in nine amphibian species from 53 aquatic systems. Infection of larvae by the trematode Ribeiroia ondatrae was associated with, and functionally related to, higher frequencies of amphibian limb malfor- mations than found in uninfected populations (#5%). Parasites were concentrated around the basal tissue of hind limbs in infected anurans, and malformations associated with infection included skin webbings, supernumerary limbs and digits, and missing or mal- formed hind limbs. In the absence of Ribeiroia, amphibian populations exhibited low (0- 5%) frequencies of abnormalities involving missing digits or distal portions of a hind limb. Species were affected differentially by the parasite, and Ambystoma macrodactylum , Hyla regilla, Rana aurora, R. luteiventris, and Taricha torosa typically exhibited the highest frequencies of abnormalities. None of the water-quality variables measured was associated with malformed amphibians, but aquatic snail hosts (Planorbella spp.) were significant predictors of the presence and abundance of Ribeiroia infection. Morphological comparisons of adult specimens of Ribeiroia collected from different sites and raised in experimental definitive hosts suggested that all samples represented the same species— R. ondatrae. These field results, coupled with experimental research on the effects of Ribeiroia on amphibians, demonstrate that Ribeiroia infection is an important and widespread cause of amphibian limb malformations in the western United States. The relevance of trematode infection to declines of amphibian populations and the influence of habitat modification on the pathology and life cycle of Ribeiroia are emphasized as areas requiring further research.

Widespread reports of malformed amphibians in North America have prompted investigations into the cause(s) and implications of the phenomenon. Recently, a trematode parasite (Ribeiroia ondatrae) was identified as the probable cause of hind-limb malformations in Pacific treefrogs (Hyla regilla) from California. We exposed a second anuran species, the western toad (Bufo boreas), to specific levels of R. ondatrae infection. In a dose-dependent manner, R. ondatrae infection induced high frequencies (40-85%) of severe limb malformations in surviving toads. Survivorship declined significantly with increasing parasite exposure, falling to 42% in the heaviest treatment. Larvae in control treatments exhibited normal development and low mortality levels. In contrast to previous experiments with R. ondatrae infection in treefrogs, cutaneous fusion was the predominant malformation among infected toads in all treatments. In - fection also caused polymely (extra limbs; fore and hind), ectromely (missing limbs), polydactyly (extra digits), and a variety of additional limb malformations. Taken together, these results demonstrate that ( i) the teratogenic effects of R. ondatrae are not limited to treefrogs, (ii) the spectrum of R. ondatrae-induced malformations is not confined to the hind limbs, and (iii) the frequency and composition of malformations resulting from infection may vary among am- phibian species. Finally, we review historical reports of limb abnormalities in the genus Bufo and discuss established and proposed causative agents, with emphasis on trematode infection and predation. Resume : Les malformations chez les amphibiens sont de plus en plus signalees en Amerique du Nord; nous avons cherche a determiner les causes et les consequences de ce phenomene. Recemment, le trematode parasite (Ribeiroia on- datrae) a ete reconnu comme la cause probable des malformations des membres posterieurs chez la Rainette du Paci- fique (Hyla regilla) en Californie. Nous avons soumis une seconde espece d'anoure, le Crapaud de l'ouest (Bufo boreas), a des infections de gravites diverses de R. ondatrae. Les infections de R. ondatrae entrainent des frequences elevees (40-85 %) de malformations serieuses des membres en fonction de la dose administree chez les crapauds survi- vants. La survie diminue significativement a mesure qu'augmente l'exposition aux parasites, jusqu'a 4 2%al asuite des traitements les plus severes. Chez les larves des groupes temoins, le developpement est normal et la mortalite est faible. Contrairement aux resultats d'experiences anterieures sur les rainettes, ici c'est la fusion cutanee qui constitue la principale malformation chez les crapauds infectes, a la suite de tous les traitements. Les infections sont aussi a l'origine de polymelies (membres surnumeraires, anterieurs et posterieurs), d'ectromelies (membres manquants), de po- lydactilies (doigts surnumeraires) et d'autres malformations des membres. Consideres dans leur ensemble, ces resultats demontrent que (i) les effets teratogenes de R. ondatrae ne sont pas restreints aux rainettes, ( ii) l'eventail des malfor- mations attribuables a R. ondatrae n'affecte pas que les membres posterieurs et (iii) la frequence et la nature des mal- formations dues aux infections peuvent varier chez les differentes especes d'amphibiens. Nous avons passe en revue tous les rapports historiques sur les malformations des membres chez Bufo et nous examinons ici les agents putatifs reconnus et supposes, en insistant sur les infections causees par les trematodes et sur la predation. (Traduit par la Redaction) 379

A new species of ectoparasitic glossiphoniid leech was found feeding on frogs in the Nature Center Pond and elsewhere in Deschutes County, Oregon. The new species of Placobdella resembles the southern alligator leech, Placobdella multilineata Moore, 1953, notwithstanding their vast geographic separation in North America. The new species is readily distinguished by possessing subdivided annuli, by its papillation and pigmentation patterns as well as by the arrangement of ovarian tissues. There is strong evidence of nocturnality and of the potential for parasitizing humans.

From 2001 to 2005, we studied the demography and seasonal movement of Oregon spotted frogs (Rana pretiosa) translocated into created ponds in Dilman Meadow in central Oregon. Our objectives were to inform future monitoring and management at the site, and to elucidate poorly known aspects of the species’ population ecology. Movement rates revealed complementary use of sites seasonally, with one small spring being preferred during winter that was rarely used during the rest of the year. Growth rates were significantly higher in ponds that were not used for breeding, and larger size resulted in significantly higher survival. When variation in survival by size was accounted for there was little variation among ponds in survival. Seasonal estimates of survival were lowest for males during the breeding/post-breeding redistribution period, suggesting a high cost of breeding for males. Overwintering survival for both genders was relatively high. Our study supports others in suggesting Oregon spotted frogs are specific in their overwintering habitat requirements, and that predator-free springs may be of particular value. We suggest that any future monitoring include measures of the rate of pond succession. Demographic monitoring should include metrics of both frog reproduction and survival: counts of egg masses at all ponds during spring, and capture-recapture study of survival in mid and late summer when capture rates are highest. Additional study of early life stages would be particularly useful to broaden our understanding of the species’ ecology. Specifically, adding intensive capture and marking effort after larval transformation in fall would enable a full understanding of the annual life cycle. Complete study of the annual life cycle is needed to isolate the life stages and mechanisms through which Oregon spotted frogs are affected by stressors such as nonnative predators. Dilman Meadow, which lacks many hypothesized stressors, is an important reference for isolating the life stages most responsive to management elsewhere in the species’ range. Oregon Spotted Frog (Rana pretiosa) Movement and Demography at Dilman Meadow: Implications for Future Monitoring By Nathan D. Chelgren, Christopher A. Pearl, Jay Bowerman, and Michael J. Adams

Amphibian chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd), has been implicated in the decline and extinction of amphibian species worldwide, in addition to catastrophic losses of animals in captivity. Conservation of threatened amphibians, including captive breeding and maintenance of animals in zoos, research facilities, and private collections, requires effective control of pathogens. Several chemical compounds, including Formalite III®, itraconazole, and chloramphenicol, have been used to treat amphibians infected with Bd, with varying levels of success. Here, we report successful clearance of Bd in five species of post-metamorphic anurans and one caudate species using terbinafine hydrochloride (HCl) in alcohol, which is available over the counter as Lamisil AT™ (Novartis Pharmaceuticals Inc., New York, NY). Treatments consisting of 5 min soak in fresh 0.01% or 0.005% terbinafine HCl in alcohol for either five consecutive days or for six treatments spread across 10 d...