Nowhere to hide: impact of a temperature-sensitive amphibian pathogen along an elevation gradient in the temperate zone

Abstract

Abstract. Amphibians are rapidly disappearing from habitats around the world and a major cause of these declines is the amphibian chytrid fungus, Batrachochytrium dendrobatidis (''Bd''). The growth rate of Bd is strongly temperature-dependent, and in areas where temperatures are well outside the envelope in which Bd has high growth rates, amphibians may be afforded a refuge from the effects of Bd. This possibility has received considerable empirical support in hot climates, but remains largely untested in cold climates. We conducted a five-year study of the impact of Bd on the declining Sierra Nevada yellow-legged frog (Rana sierrae) across an elevation/temperature gradient in Yosemite National Park using three approaches: (1) resurveys of all 285 R. sierrae populations to describe the landscape-scale patterns of Bd infection intensity, frog population size, and frog population persistence; (2) detailed description of seasonal patterns in temperatures and corresponding Bd infection intensities on R. sierrae; and (3) a frog translocation experiment in which infected R. sierrae from a single source lake were introduced into each of five lakes along an elevation gradient. We predicted that infection intensity should decrease with increasing elevation (i.e., decreasing temperature), and consequently frog survival, population size, and population persistence should increase with elevation. Results from resurveys indicated that frog population size increased with elevation but Bd infection intensity and frog population persistence were unrelated to elevation. Seasonal temperatures varied widely but had no significant effect on Bd infection intensity. Results from the translocation experiment indicated that Bd infection intensity and frog survival following translocation were also unrelated to water temperature. Therefore, contrary to the widely-accepted paradigm that cold environments should strongly limit effects of Bd on amphibians, we found little or no evidence of such limitation at even the highest elevations. Therefore, in temperate montane ecosystems it is unlikely that high elevations will provide amphibians with a refuge from Bd.

The pathogen Batrachochytrium dendrobatidis disturbs the frog skin microbiome during a natural epidemic and experimental infection

“…(Enzootic and epizootic refer to disease dynamics in animals, analagous to endemic and epidemic dynamics of human diseases.) Three of the populations in this study (Mono, Unicorn, and Conness) show enzootic Bd dynamics, characterized by moderate Bd loads and long-term frog population persistence despite Bd infection (27,49). Census and infection data show these populations have been infected with Bd since 2004 or earlier, with no sign of population decline (27,49).…”

“…This study was conducted in four R. sierrae populations in the Sierra Nevada of California (specifically Yosemite National Park and Sierra National Forest). Our group has collected census and Bd infection data on these populations as well as others since 2004 or earlier (27,49). For the current study, each population was surveyed three to four times between July and September 2010, and at least once in 2011 (Table S1).…”

“…Three of the populations in this study (Mono, Unicorn, and Conness) show enzootic Bd dynamics, characterized by moderate Bd loads and long-term frog population persistence despite Bd infection (27,49). Census and infection data show these populations have been infected with Bd since 2004 or earlier, with no sign of population decline (27,49). The fourth population (Marmot) first showed signs of Bd infection in late 2010, which rapidly developed into an epizootic (with maximum Bd loads rising from 0 to over 150,000 zoospores in under 2 mo) that resulted in catastrophic population decline, with no postmetamorphic frogs found during censuses the following summer (Table S1).…”

Large-scale recovery of an endangered amphibian despite ongoing exposure to multiple stressors

“…These increases are occurring over a large landscape and across hundreds of populations, providing a rare example of amphibian recovery at an ecologically relevant spatial scale. That said, recovery of R. sierrae in Yosemite is far from complete and at a minimum, will require the continued removal of introduced fish from key habitats and translocation of frogs to reestablish populations in areas from which they are extirpated (21). However, our research in the Sierra Nevadaand complimentary work in Australia (30, 31)-suggests that amphibian declines may be at least partially reversible at a regional scale.…”

Temporal and spatial variation of atmospherically deposited organic contaminants at high elevation in yosemite national park, California, USA

“…Lakes were separated from each other by 5 to 15 km. The lakes were selected as part of a companion study of the frog Rana sierrae to represent highelevation water bodies that were permanent, !3 m deep, lacked introduced fish, and could be reached by hiking within 1 d from a trailhead [17]. All four lakes were considered representative of high-elevation lakes in the central Sierra Nevada with respect to size, hydrology, and biota.…”