Rana Aurora Research Articles

Carryover Aquatic Effects On Survival Of Metamorphic Frogs During Pond Emigration

In organisms with complex life cycles, physiological stressors during early life stages may have fitness-level impacts that are delayed into later stages or habitats. We tested the hypothesis that body size and date of metamorphosis, which are highly responsive to aquatic stressors, influence post-metamorphic survival and movement patterns in the terrestrial phase of an ephemeral pond-breeding frog by examining these traits in two populations of northern red-legged frogs (Rana aurora aurora). To increase variation of body size at metamorphosis, we manipulated food availability for 314 of 1045 uniquely marked tadpoles and estimated the probability that frogs survived and emigrated using concentric rings of drift fencing surrounding ponds and Bayesian capture-recapture modeling. The odds of surviving and emigrating from the ponds to the innermost drift fences, approximately 12 m, increased by factors of 2.20 (95% credibility intervals 1.39-4.23) and 2.54 (0.94-4.91) with each millimeter increase in snout-vent length and decreased by factors of 0.91 (0.85-0.96) and 0.89 (0.80-1.00) with each day's delay in metamorphosis for the two ponds. The odds of surviving and moving to the next ring of fencing, 12 m to approximately 40 m from the ponds, increased by a factor of 1.20 (0.45-4.06) with each millimeter increase in size. Our results demonstrated that body size and timing of metamorphosis relate strongly to the performance of newly metamorphosed frogs during their initial transition into terrestrial habitat. Carryover effects of aquatic stressors that reduce size and delay metamorphosis may have population-level impacts that are not expressed until terrestrial stages. Since changes in both aquatic and terrestrial systems are implicated in many amphibian declines, quantifying both immediate and delayed effects of stressors on demographic rates is critical to sound management.

AMPHIBIAN USE OF CHEHALIS RIVER FLOODPLAIN WETLANDS

Abstract The use of isolated emergent wetlands by amphibians has been well documented. However, amphibian habitats such as emergent wetlands in floodplains may differ from isolated wetlands because of their high disturbance (water fluctuation) related to riverine flooding, presence of fish species, and increased connectivity among aquatic habitats. We compared the amphibian assemblages at 6 freshwater wetland habitats in the Chehalis River floodplain and examined the effect of wetland restoration on amphibians. We sampled 6 wetlands during the breeding season in 2003 and 2004 and captured over 15,000 adults, tadpoles, and larvae from 6 species. The red-legged frog (Rana aurora) was the most abundant species captured. The rough skinned newt (Taricha granulose) was the only amphibian captured at all sampled sites. Although it is more desirable to prevent wetland degradation from occurring, restored and enhanced wetlands in floodplains do provide breeding habitat for amphibians. Amphibian species captured in...

Effects of nitrate and the pathogenic water mold Saprolegnia on survival of amphibian larvae

We tested for a synergism between nitrate and Saprolegnia, a pathogenic water mold, using larvae of 3 amphibian species: Ambystoma gracile (northwestern salamander), Hyla regilla (Pacific treefrog) and Rana aurora (red-legged frog). Each species was tested separately, using a 3 x 2 fully factorial experiment with 3 nitrate treatments (none, low and high) and 2 Saprolegnia treatments (Saprolegnia and control). Survival of H. regilla was not affected significantly by either experimental factor. In contrast, survival of R. aurora was affected by a less-than-additive interaction between Saprolegnia and nitrate. Survival of R. aurora was significantly lower in the Saprolegnia compared to the control treatment when nitrate was not added, but there was no significant difference in survival between Saprolegnia and control treatments in the low and high nitrate treatments, consistent with increased nitrate preventing Saprolegnia from causing mortality of R. aurora. Survival of A. gracile followed a similar pattern, but the difference between Saprolegnia and control treatments when nitrate was not added was not significant, nor was the nitrate x Saprolegnia interaction. Our study suggests that Saprolegnia can cause mortality in amphibian larvae, that there are interspecific differences in susceptibility and that the effects of Saprolegnia on amphibians are context-dependent.

Evidence from peptidomic analysis of skin secretions that the red-legged frogs, Rana aurora draytonii and Rana aurora aurora, are distinct species

The northern red-legged frog Rana aurora aurora and the California red-legged frog Rana aurora draytonii are traditionally classified together in the same species group. Ten peptides with antimicrobial activity were isolated from norepinephrine-stimulated skin secretions of R. aurora draytonii and purified to near homogeneity. The peptides were identified as belonging to the ranatuerin-2 family (two peptides), brevinin-1 family (four peptides), temporin family (three peptides), and a novel peptide, RV-23 (RIGVLLARLPKLFSLFKLMGKKV) that has limited structural similarity to the bee venom peptide, melittin. This distribution of peptides contrasts with that found previously in skin secretions from R. aurora aurora collected under the same conditions and at the same time of year (one ranatuerin-2 peptide, two brevinin-1 peptides, and one temporin peptide). The variation in amino acid sequences between corresponding R. aurora draytonii and R. aurora aurora peptides is comparable with the variation in sequences of orthologs from other members of the Amerana group of New World ranid frogs ( Rana boylii, Rana muscosa, and Rana luteiventris). It is proposed, therefore, that the red-legged frogs should be regarded as separate species ( R. aurora and R. draytonii) within the Amerana group rather than conspecific subspecies. The data emphasize that amino acid sequences of antimicrobial peptides in skin secretions may be used to infer taxonomic and phylogenetic relationships between species of ranid frogs.

Three Rarely Reported Digeneans Inhabiting Amphibians From Vancouver Island, British Columbia, Canada

Three rarely reported species of digeneans were collected in amphibian hosts from Diversion Reservoir, Sooke, Vancouver Island, British Columbia, Canada. The endangered anuran Rana aurora hosted Glypthelmins californiensis, Gorgoderina multilobata, and Megalodiscus microphagus. In addition, the anuran Pseudacris regilla and the caudatan Taricha granulosa hosted Megalodiscus microphagus. Gorgoderina multilobata has been reported only once since 1936 and has never been reported outside of California. We note several characters not previously reported for Gorgoderina multilobata and G. aurora.

PREDATION ON RED TREE VOLES BY OWLS AND DIURNAL RAPTORS

*HAYES MP 1997. Status of the Oregon spotted frog (Rana pretiosa sensu stricto) in the Deschutes Basin and selected other systems in Oregon and northeastern California with a rangewide synopsis of the species' status. Unpublished report prepared for the Nature Conservancy, Portland, OR. 57 p. + Appendices. Available from U. S. Fish and Wildlife Service, 26000 SE 98th Avenue, Portland, OR 97266. LICHT LE. 1986. Food and feeding behavior of sympatric red-legged frogs, Rana aurora, and spotted frogs, Rana pretiosa, in southwestern British Columbia. Canadian Field Naturalist 100:22-31. MCALLISTER KR, LEONARD WP, STORM RM. 1993. Spotted frog (Rana pretiosa) surveys in the Puget Trough of Washington, 1989-1991. Northwestern Naturalist 74:10-15.

DECLINING DOWNWIND: AMPHIBIAN POPULATION DECLINES IN CALIFORNIA AND HISTORICAL PESTICIDE USE

Pesticides have long been proposed as a possible cause of amphibian pop- ulation declines, but due to a number of challenges there has been relatively little ecotox- icological research on pesticides and declines in natural populations. My study examines the association between the spatial patterns of declines for five California amphibian species and historical patterns of pesticide use in California from 1974 to 1991 based on Department of Pesticide Regulation records. Information on declines was derived from maps of historical sites and current population status for the Yosemite toad (Bufo canorus), California red- legged frog (Rana aurora draytonii), foothill yellow-legged frog (R. boylii), Cascades frog (R. cascadae), and the mountain yellow-legged frog (R. muscosa). Multiple logistic- regression and generalized additive models were used to analyze the relationship between site status (present or absent) and total upwind pesticide use, 64 pesticide classes and groups, and covariates including precipitation, elevation, surrounding urban and agricultural land use, and spatial location. Total pesticide use was a strong, significant variable in logistic-regression models for all species, except B. canorus. Total pesticide use was a significant variable even when spatial autocorrelation was accounted for by inclusion of a spatial location covariate. Cholinesterase-inhibiting pesticides (most organophosphates and carbamates) stood out as more strongly associated with population declines than any other class of pesticides. This is the first study in which population declines of multiple declining

Host-defense peptides isolated from the skin secretions of the Northern red-legged frog Rana aurora aurora

Antimicrobial peptides in the skin secretions of anurans constitute a component of the innate immunity that protects the organism against invading pathogens. Four peptides with antimicrobial activity were isolated in high yield from norepinephrine-stimulated skin secretions of the Northern red-legged frog Rana aurora aurora and their primary structures determined. Ranatuerin-2AUa (GILSSFKGVAKGVAKNLAGKLLDELKCKITGC) showed potent growth-inhibitory activity against a range of Gram-positive and Gram-negative bacteria (minimum inhibitory concentrations <20 μM) but low hemolytic activity against human erythrocytes (50% hemolysis at 290 μM). Brevinin-1AUa (FLPILAGLAAKLVPKVFCSITKKC) and brevinin-1AUb (FLPILAGLAANILPKVFCSITKKC) also showed potent antimicrobial activity but were strongly hemolytic (HC 50<10 μM). Temporin-1AUa (FLPIIGQLLSGLL.NH 2) atypically lacked a basic amino acid residue and showed very weak antimicrobial and hemolytic activity. Its biological function remains to be established. The primary structures of the antimicrobial peptides are consistent with a close phylogenetic relationship between R. aurora, Rana boylii and Rana luteiventris.

Co-secretion of soluble caveolin-1 and pepsinogen in the oesophagus of the red-legged frog Rana aurora aurora

Caveolin-1, an integral membrane protein, is the principal component of caveolae, which are specialised vesicular microdomains of the plasma membrane. Caveolae are found in most cell types, but they are most abundant in adipocytes, endothelial cells, fibroblasts, and muscle cells. Functionally, they have been implicated in endothelial transcytosis, potocytosis, and signal transduction. Recently, caveolin-1 has been found unexpectedly in the cytoplasm, mitochondria and elements of the secretory pathways of exocrine secretory cells. We have co-localised caveolin-1 and pepsinogen immunohistochemically in serous cells of oesophageal glands of the red-legged frog, Rana aurora aurora. Thus, according to its intracellular localisation pattern, caveolin-1 may be either a soluble protein, located in secretory droplets, or a protein that is inserted in caveolar membranes. Soluble caveolin-1, which is probably embedded in a lipid particle surrounded by a phospholipid shell, may be involved in intracellular and extracellular lipid transport. In the gut, caveolin-1-rich lipid particles can act as donor particles to facilitate (protein-mediated) intestinal uptake of cholesterol and phospholipids. Our findings strengthen the hypothesis that caveolin-1 has a physiological autocrine/paracrine function and demonstrate that secretion of this protein also occurs in vertebrates other than mammals, such as amphibians, which may be a useful alternative animal model to study caveolin-1.

Asymmetrical Effects of Introduced Bullfrogs (Rana catesbeiana) on Native Ranid Frogs in Oregon

Introduced American Bullfrogs (Rana catesbeiana) have become widely established in the Pacific Northwest over the last century and are thought to be an important predator of native amphibians throughout the western United States. The Northern Red-Legged Frog (Rana aurora aurora) and Oregon Spotted Frog (Rana pretiosa) historically coexisted in portions of the Pacific Northwest now invaded by R. catesbeiana, but R. pretiosa has declined more severely than R. a. aurora. We investigated whether microhabitat and behavioral differences that facilitate sympatric coexistence of the natives predict which species is more susceptible to predation by introduced R. catesbeiana. Our laboratory experiments demonstrate that R. catesbeiana adults prefer aquatic microhabitats, that R. pretiosa juveniles are more aquatic than R. a. aurora, and that adult R. catesbeiana consume more R. pretiosa than R. a. aurora juveniles. Mean and maximum jump distances of R. pretiosa were shorter than equally sized R. a. aurora, and the difference between these two species increased with larger frog sizes. Our examination of field survey data indicates that R. pretiosa coexist with R. catesbeiana less frequently than R. a. aurora. We conclude that R. catesbeiana is a greater threat to survival of R. pretiosa than to R. a. aurora and suggest that microhabitat use and escape abilities of native ranid frogs may be linked to this asymmetrical effect. Analysis of behavioral and microhabitat differences among related native species may be a useful tool in predicting the effects of introduced predators on amphibians and can assist in developing conservation priorities for these species.

Bullfrogs, Disturbance Regimes, and the Persistence of California Red-Legged Frogs

The introduction and spread of bullfrogs (Rana catesbeiana) in western North America may have played a central role in the declines of native ranid frogs. Specifically, a positive corielation exists between the absence of California red-legged frogs (Rana aurora draytonii) and the presence of introduced bullfrogs, but coexistence does occur in some environments. Enclosure experiments and diet studies have shown that bullfrogs prey on larval and juvenile California red-legged frogs. We used a modeling approach to quantify the threat of bullfrog predation on California red-legged frog populations. We created age-structured population models for both species. We used these models to (I) explore the sensitivity of red-legged frog populations to changes in the intensity of bullfrog predation; (2) explore the hypothesis that high flood frequencies increase the probability for coexistence in southern California streams; and (3) examine the efficacy of bullfrog management strategies, such as shooting adults and draining livestock grazing ponds. Our model simulations indicated that winter floods, which strongly increase mortality of bullfrogs but not red-legged frogs, facilitate coexistence if they occur more than once every 5 years. We found that increasing adult bullfrog mortality through shooting would benefit red-legged frogs only with extreme effort. Conversely, the draining of livestock grazing ponds can be effective in bullfrog management if claiming occurs at least every 2 years. Shooting and draining in tandem were successful at decreasing bullfrog densities. Finally, our model provided a quantitative measure of bullfrog predation on California red-legged frogs that can potentially be used to assess the impact of bullfrogs on a site-by-site basis. Our model plus experimental studies that link specific environmental factors to the bullfrog predation rate, can provide managers with a useful tool for controlling populations and facilitating conservation efforts for the California red-legged frog.

Behavioral Responses of Anuran Larvae to Chemical Cues of Native and Introduced Predators in the Pacific Northwestern United States

We compared behavioral responses of larvae of three Pacific Northwest anurans from different hydroperiods to water borne cues of native and introduced predators. Two native anurans (Pacific Treefrog, Pseudacris regilla, and Northern Red-Legged Frog, Rana aurora aurora) and introduced Bullfrogs (Rana catesbeiana) responded to water conditioned by native Redside Shiners (Richardsonius balteatus) by increasing refuge use. The larvae of the two native anurans differed in their response to introduced predator cues. Rana aurora aurora, which occur in temporary and permanent waters, responded to both introduced Bluegill Sunfish (Lepomis macrochirus) and introduced Crayfish (Procambarus clarkii). Pseudacris regilla, which occur primarily in temporary ponds, did not respond to water borne cues from either introduced predator. The broader responses of R. a. aurora may indicate greater behavioral plasticity or more exposure to novel predators than experienced by P. regilla. Larvae of introduced R. catesbeiana responded strongly to cues from two fish native to the Pacific northwest but did not alter behavior in response to any of five potential predators with which they coexist in their native range. Fish that occur with R. catesbeiana in their native range generally find Bullfrog larvae unpalatable. This pattern suggests that Bullfrog larvae can recognize cues of novel predators that may find them palatable, which could contribute to their success as an invasive species in the region.

Terrestrial activity and conservation of adult California red-legged frogs Rana aurora draytonii in coastal forests and grasslands

The federally threatened California red-legged frog Rana aurora draytonii occupies both aquatic and terrestrial habitats in its adult life stage. The terrestrial activities of this species are not well known and require documentation to assist in the development of appropriate levels of protection under the US Endangered Species Act. We studied the terrestrial activities of radio-tagged red-legged frogs ( n=8–26) inhabiting a coastal watershed in Santa Cruz County, California, during 1997–1998. In particular, we investigated (1) the use of terrestrial habitats by non-migrating adults in relation to season, breeding chronology, and precipitation, and (2) adult migration behavior, including seasonal timing, duration, distances traveled, and the use of corridors. Non-migrating red-legged frogs occupied terrestrial habitats briefly (median=4–6 days) following infrequent summer rains, but resided nearly continuously on land (median=20–30 days) from the onset of the winter wet-season until breeding activities commenced 1–2 months later. All of the non-migrating frogs remained within 130 m of their aquatic site of residence (median <25 m). Intervals spent on land were again brief during mid/late winter (median=1–4 days), despite frequent and copious rainfall. Adult migration to and from breeding sites occurred from late October through mid-May (wet season). We monitored 25 migration events between aquatic sites that were 200–2800 m apart. Short distance movements (<300 m) were completed in 1–3 days, longer movements required up to 2 months. Most migrating frogs moved overland in approximately straight lines to target sites without apparent regard to vegetation type or topography. Riparian corridors were neither essential nor preferred as migration routes. Frogs traveling overland occurred in upland habitats as far as 500 m from water. Approximately 11–22% of the adult population was estimated to migrate to and from breeding sites annually, whereas the bulk of the adult population was resident at these sites. Adequate protection of red-legged frog populations inhabiting relatively undeveloped landscapes is liable to be achieved by retaining an array of suitable habitat elements within at least 100 m of occupied aquatic sites, and by imposing seasonal limitations on detrimental human activities occurring within this zone. Specific protections for migrating frogs are probably unwarranted in forest and rangeland environments because dispersal habitat is ubiquitous and migrating frogs are widely distributed across the landscape in space and time.

Predation risk and competition effects on the life-history characteristics of larval Oregon spotted frog and larval red-legged frog.

We conducted an artificial pond experiment to test hypotheses about the effects of competition and non-lethal predator cues on metamorphic characteristics of sympatric Oregon spotted frogs (Rana pretiosa) and red-legged frogs (Rana aurora) in southwestern British Columbia. Tadpoles were exposed to the presence or absence of one another, two density levels and to the presence or absence of predacious odonate larvae (Aeshna palmata) isolated in enclosures. In the artificial pond study, R. aurora were significantly larger at metamorphosis (12%) and exhibited only slightly longer larval periods when exposed to Aeshna. In the presence of R. pretiosa, they significantly decreased time to metamorphosis, and were significantly larger at metamorphosis (12%) than those reared alone. Rana pretiosa in treatments with R. aurora were somewhat larger at metamorphosis when a non-lethal predator was present, and in treatments where R. pretiosa were alone with a predator tadpole mass at metamorphosis was smaller than those in the absence of Aeshna, but these results were not statistically significant. Both species reduced activity and moved away from the predator in the presence of an enclosed dragonfly larva in the laboratory. Most tadpole mesocosm experiments have found that the trade-off between size and timing of metamorphosis is extremely important to amphibians, but we suggest that the trade-off discussed in traditional amphibian models may not apply to species like R. pretiosa that are exposed to the same gape-limited predators upon reaching metamorphosis.

What Is Missing in Amphibian Decline Research: Insights from Ecological Sensitivity Analysis

Abstract: Inventory, monitoring, and experimental studies have been the primary approaches for documenting and understanding the problem of amphibian declines. However, little attention has been given to placing human‐caused perturbations affecting one or more life‐history stages in the context of the overall population dynamics of particular species. We used two types of ecological sensitivity analysis to determine which vital rates have the strongest influence on the population dynamics of western toads ( Bufo boreas), red‐legged frogs ( Rana aurora), and common frogs ( Rana temporaria), pond‐breeding amphibians that have declined in all or portions of their ranges. Our results suggest that post‐metamorphic vital rates and highly variable vital rates both have a strong influence on the population dynamics of these species and therefore deserve more research and management attention. Ecological sensitivity analysis should be more widely applied to the issue of amphibian declines in order to identify the most plausible mechanisms of decline and prioritize which life‐history stages should be the focus of research and management efforts. Future experimental studies of perturbations in one or more life‐history stage should attempt to link the magnitude of the perturbation measured with the overall population‐level consequences. Finally, current research, inventory, and monitoring efforts should be supplemented with demographic studies so that quantitative analyses can be applied to a wider range of species and life‐history groups.

PARASITE (RIBEIROIA ONDATRAE) INFECTION LINKED TO AMPHIBIAN MALFORMATIONS IN THE WESTERN UNITED STATES

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.

Response of Forest Floor Vertebrates to Riparian Hardwood Conversion Along the Bear River, Southwest Washington

Abstract The conversion of riparian red alder (Alnus rubra) forest to conifers for salmon (Oncorhynchus spp.) habitat improvement is controversial. I monitored changes in vegetation, microclimate, and the abundance, distribution, and body condition of small mammals and amphibians during the initial stage of alder conversion. Treatments reduced alder and moss cover [mean standardized effect size (ES) = -2.38 and -1.23, respectively (P = 0.0001)], but increased shrub and forb cover [ES = 0.98 and 0.37, respectively (P = 0.0001)]. Treatment effects on microclimate were neutral to moderate (ES = 0.00 to 0.67, P = 0.2). Effects on pitfall trap capture rates of small mammals were small to moderate (ES = -0.04 to 0.51, P = 0.2) and varied by taxon, and effects on captures of amphibians were small (P = 0.2), but positive (ES = 0.05 to 0.26). Pitfall captures were influenced more by seasonal weather patterns than treatment effects on vegetation. Differences in the density of torrent salamanders (Rhyacotriton kezeri) in streams in conversion and control sites were large (ES = -1.00, P = 0.4) and moderate for giant salamanders [ Dicamptodon spp. (ES = 0.31, P = 0.4)]. Treatment effects on the mass/individual for three species of shrew were small (P = 0.2 to 0.9) and either negative or neutral (ES = -0.21 to 0.00) for juveniles and adults. Effects on the mass of western red-backed salamanders (Plethodon vehiculum) were small for adults (ES = -0.12, P = 0.6) and juveniles (ES = 0.08, P = 0.8). Treatment effect on the mass of red-legged frogs (Rana aurora) was positive ( P = 0.2) for both age classes (adult ES = 0.52, juvenile ES = 0.20). The effect of conversion on the mass of torrent salamanders was positive (adult ES = 1.00, P = 0.002; juvenile ES = 0.25, P = 0.02). Additional research should focus on confirming my results, longer term effects, and additional wildlife species. FOR. SCI. 48(2):299–308.

Effects of agricultural runoff on native amphibians in the Lower Fraser River Valley, British Columbia, Canada

AbstractHatching success, deformity rates, and survivorship of northern red‐legged frogs (Rana aurora) and northwestern salamanders (Ambystoma gracile) were assessed at three agricultural and three reference sites in the Sumas Prairie, British Columbia, Canada. In 1997 and 1998, eggs of both species and eggs of R. aurora, respectively, were placed in Nytex mesh cages (Irwindale, CA, USA) in roadside ditches at each site. Concurrently in 1997, eggs of R. aurora were reared in the laboratory but were exposed to water samples from each of the study sites. Hatching success was significantly lower at all agricultural sites compared to the reference sites for both species. However, no differences were observed in hatching success among sites for eggs of R. aurora reared in the laboratory. Water chemistry differed among all sites, but the largest differences were between reference and agricultural sites. Ammonia (maximum of 1.27 mg/L), total phosphate (maximum of 8.14 mg/L), and biological oxygen demand (maximum of 79.00 mg/L) were high at some of the agricultural sites during the development period. Results suggest that agricultural runoff may contribute to lower reproductive success and ultimately to reduced population viability of amphibian populations in the Lower Fraser Valley (BC, Canada).

Exposure of red-legged frog embryos to ambient UV-B radiation in the field negatively affects larval growth and development.

Exposure to ultraviolet-B radiation (UV-B; 280-320nm) has a wide array of effects on aquatic organisms, including amphibians, and has been implicated as a possible factor contributing to global declines and range reductions in amphibian populations. Both lethal and sublethal effects of UV-B exposure have been documented for many amphibian species at various life-history stages. Some species, such as red legged frogs, Rana aurora, appear to be resistant to current ambient levels of UV-B, at least at the embryonic and larval stages, despite the fact that they have experienced range reductions in the Willamette Valley of Oregon, USA. However, UV-B is lethal to embryonic and larval R. aurora at levels slightly above those currently experienced during development. Therefore, we predicted that exposure of embryos to ambient UV-B radiation would result in sublethal effects on larval growth and development. We tested this by exposing R. aurora embryos to ambient UV-B in the field and then raising individuals in the laboratory for 1month after hatching. Larvae that were exposed to UV-B as embryos were smaller and less developed than the non-exposed individuals 1month post-hatching. These types of sublethal effects of UV-B exposure indicate that current levels of UV-B could already be influencing amphibian development.

Organochlorine pesticides and polychlorinated biphenyls (PCBs) in eggs of red-legged frogs ( Rana aurora) and northwestern salamanders ( Ambystoma gracile) in an agricultural landscape

Organochlorine pesticides were widely used in the past in Sumas Prairie, British Columbia, Canada. In the 1990s, the hatching success of amphibians from agricultural sites was significantly depressed in the Sumas Prairie compared to reference sites. Therefore, in this study, organochlorine pesticides and polychlorinated biphenyls (PCBs) were measured in eggs of red-legged frogs ( Rana aurora) and northwestern salamanders ( Ambystoma gracile) from the Sumas Prairie. Egg masses were sampled from three agricultural sites that were exposed to agricultural runoff, and three reference sites that had lower agricultural runoff exposures. Not only was there little difference in contamination between agricultural and reference sites, but the levels of pesticides and PCBs found were lower than the concentrations reported to cause developmental or behavioural problems in amphibians.