Distribution of boreal toad populations in relation to estimated UV-B dose in Glacier National Park, Montana, USA

Abstract

A recent increase in ultraviolet B radiation is one hypothesis advanced to explain suspected or documented declines of the boreal toad (Bufo boreas Baird and Girard, 1852) across much of the western USA, where some experiments have shown ambient UV-B can reduce embryo survival. We examined B. boreas occupancy relative to daily UV-B dose at 172 potential breeding sites in Glacier National Park, Montana, to assess whether UV-B limits the distribution of toads. Dose estimates were based on ground-level UV-B data and the effects of elevation, local topographic and vegetative features, and attenuation in the water column. We also examined temporal trends in surface UV-B and spring snowpack to determine whether populations are likely to have experienced increased UV-B exposure in recent decades. We found no support for the hypothesis that UV-B limits the distribution of populations in the park, even when we analyzed high-elevation ponds separately. Instead, toads were more likely to breed in water bodies with higher estimated UV-B doses. The lack of a detectable trend in surface UV-B since 1979, combined with earlier snow melt in the region and increasing forest density at high elevations, suggests B. boreas embryos and larvae likely have not experienced increased UV-B.RCsumk : L'augmentation rCcente de le rayonnement ultraviolet B est l'une des hypothbses avanc6es pour expliquer les dCclins apprChendCs ou observCs du crapaud de l'ouest (Bufo boreas Baird et Girard, 1852) dans presque tout l'ouest des 8.-u.; certaines expCriences y ont d'ailleurs dCmontrC que 1'UV-B ambiant peut rCduire la survie des embryons. Nous avons dCterminC l'occupation du territoire par B. boreas en fonction des doses journalibres d'UV-B B 172 sites potentiels de reproduction dans le parc national Glacier, Montana, afin d'kvaluer si 1'UV-B limite la rkpartition des crapauds. Les estimations du dosage ont 6tC basCes sur des mesures d'UV-B au niveau du sol et sur les effets de l'altitude, de la topographie locale, des caract6ristiques de la v6g6tation et de l'att6nuation dans la colonne d'eau. Nous avons aussi examink les variations temporelles de 1'UV-B en surface, ainsi que la couche de neige au printemps de savoir si les populations ont pu Ctre soumises B des expositions accrues au cours des dernikres dkcennies. Nous n'avons rien trouvC qui appuie l'hypothbse selon laquelle 1'UV-B limite la rCpartition de la population dans le parc, mCme lorsque nous analysons les donnCes sur les Ctangs de haute altitude s6parCment. Au contraire, les crapauds sont plus susceptibles de se reproduire dans les masses d'eau qui re~oivent les doses estimCes d'UV-B les plus fortes. L'absence de tendance d6celable de 1'UV-B en surface depuis 1979, combinCe B une fonte des neiges plus pr6coce dans la region et une densit6 accrue des forCts en haute altitude, laisse croire que les embryons et les larves de B. boreas n'ont vraisemblablement pas Ct C exposCs B une augmentation de 1'UV-B.[Traduit par la RCdaction]

Ambient Ultraviolet B Radiation and Prevalence of Infection by Batrachochytrium dendrobatidis in Two Amphibian Species

“…Our data on common toads and European midwife toads suggest that exposure to UV‐B is inversely correlated with the probability of infection and that in midwife toads this effect is independent of elevation. Hossack et al (2006) found that the probability of occurrence of western toads in ponds in Glacier National Park (Montana, USA) increased slightly as UV‐B increases. However, they did not test whether Bd or other pathogens were present.…”

Responses of Pond-Breeding Amphibians to Wildfire: Short-Term Patterns in Occupancy and Colonization

“…We found B. boreas breeding in .20 wetlands the year after that wildfire burned an area where extensive surveys had identified only three breeding sites between 1999 and 2002 (B. R. Hossack and P. S. Corn, unpublished data). Hypotheses to explain the apparent attraction of recently burned habitats include (1) the terrestrial environment provides more optimal thermal conditions for juveniles and adults (G. Guscio and L. Eby, unpublished report to USGS), and (2) burned wetlands provide better oviposition habitats (Hossack et al 2006b). However, we found no differences in the temperature of burned wetlands that were used for breeding compared to those that were not used (B. R. Hossack et al, unpublished manuscript).…”

Effects of UV radiation on aquatic ecosystems and interactions with climate change

“…232 Field studies of the boreal toad in Glacier National Park, Montana, USA, indicate that UV-B exposure does not limit distribution, and breeding was actually higher in high UV radiation habitats. 233 UV radiation has important interactive effects with other environmental stressors, including delayed development rates in frog tadpoles when exposed to UV-B radiation and environmentally realistic concentrations of 4-tert-octylphenol, an estrogenic microbial decomposition product of widely used industrial surfactants, 234 and a seven-fold increase in lethality of UV-B radiation when toad tadpoles were exposed in the presence of nitrite. 235 There is also some evidence that prior exposure to UV radiation may confer resistance to the interactive effects of UV radiation and toxic compounds, a phenomenon known as cotolerance.…”