Dynamics of Chytrid Fungus (Batrachochytrium Dendrobatidis) Infection in Amphibians in the Rincon Mountains and Tucson, Arizona

The chytrid fungus Batrachochytrium dendrobatidis (Bd) has been implicated in amphibian declines around the world, including the southwestern United States. I studied patterns of Bd infection in Hyla arenicolor, Rana catesbeiana, and R. yavapaiensis in the Rincon Mountains and Tucson Basin in Arizona. Bd prevalence and infection intensity were location dependent in all species and R. yavapaiensis may be a reservoir of Bd for H. arenicolor, where they co-occurred. Treatment of a backyard population of R. yavapaiensis with itraconazole did not reduce winter frog mortality due to Bd. The lethal Bd infection threshold of this population was between 59,847 and 4,237,330 zoospores. Zoospore loads from swabs of freshly dead frogs did not differ significantly from those taken from those same frogs following freezing and thawing. Thus, important information regarding infection intensity and probable cause of death can be gathered from frogs collected by others and frozen until convenient to process

Dynamics of chytrid fungus (Batrachochytrium dendrobatidis) infection in amphibians in the Rincon Mountains and Tucson, Arizona

The chytrid fungus Batrachochytrium dendrobatidis (Bd) has been implicated in amphibian declines around the world, including the southwestern United States. I studied patterns of Bd infection in Hyla arenicolor, Rana catesbeiana, and R. yavapaiensis in the Rincon Mountains and Tucson Basin in Arizona. Bd prevalence and infection intensity were location dependent in all species and R. yavapaiensis may be a reservoir of Bd for H. arenicolor, where they co-occurred. Treatment of a backyard population of R. yavapaiensis with itraconazole did not reduce winter frog mortality due to Bd. The lethal Bd infection threshold of this population was between 59,847 and 4,237,330 zoospores. Zoospore loads from swabs of freshly dead frogs did not differ significantly from those taken from those same frogs following freezing and thawing. Thus, important information regarding infection intensity and probable cause of death can be gathered from frogs collected by others and frozen until convenient to process

Hydrologic variability governs population dynamics of a vulnerable amphibian in an arid environment.

Dynamics of many amphibian populations are governed by the distribution and availability of water. Therefore, understanding the hydrological mechanisms that explain spatial and temporal variation in occupancy and abundance will improve our ability to conserve and recover populations of vulnerable amphibians. We used 16 years of survey data from intermittent mountain streams in the Sonoran Desert to evaluate how availability of surface water affected survival and adult recruitment of a threatened amphibian, the lowland leopard frog (Lithobates yavapaiensis). Across the entire study period, monthly survival of adults ranged from 0.72 to 0.99 during summer and 0.59 to 0.94 during winter and increased with availability of surface water (Z = 7.66; P < 0.01). Recruitment of frogs into the adult age class occurred primarily during winter and ranged from 1.9 to 3.8 individuals/season/pool; like survival, recruitment increased with availability of surface water (Z = 3.67; P < 0.01). Although abundance of frogs varied across seasons and years, we found no evidence of a systematic trend during the 16-year study period. Given the strong influence of surface water on population dynamics of leopard frogs, conservation of many riparian obligates in this and similar arid regions likely depends critically on minimizing threats to structures and ecosystem processes that maintain surface waters. Understanding the influence of surface-water availability on riparian organisms is particularly important because climate change is likely to decrease precipitation and increase ambient temperatures in desert riparian systems, both of which have the potential to alter fundamentally the hydrology of these systems

Estimated abundance of adult lowland leopard frogs in the Rincon Mountains, Arizona, USA between 1996 and 2011.

<p>Estimated number of adult lowland leopard frogs, with 95% confidence intervals, in four canyons in the Rincon Mountains during spring (1 May–15 July) and fall (1 October–30 November). Estimates were obtained using empirical Bayes methods based on a model of recruitment as a function of season, seasonal water availability, number of pools per complex, and connectivity, and a model of survival as a function of season and seasonal water availability (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0125670#pone.0125670.t002" target="_blank">Table 2</a>).</p

Estimated abundance of adult lowland leopard frogs in the Rincon Mountains, Arizona, USA between 1996 and 2011 as a function of regional precipitation for 12 months immediately preceding each sampling period.

<p>Estimated number of adult lowland leopard frogs, with 95% confidence intervals, in four canyons in the Rincon Mountains during spring (1 May–15 July) and fall (1 October–30 November). Estimates were obtained using empirical Bayes methods based on a model of recruitment as a function of season, seasonal water availability, number of pools per complex, and connectivity, and a model of survival as a function of season and seasonal water availability (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0125670#pone.0125670.t002" target="_blank">Table 2</a>). We obtained regional precipitation data from an Arizona Meteorological Network weather station in Tucson, AZ located approximately 25 km from our study area. For spring sampling periods, we summed monthly precipitation totals from May–April; for fall sampling periods, we summed monthly precipitation totals from October–September. The solid line represents a linear regression of abundance on precipitation.</p

Predicted number of recruits and monthly survival of adult lowland leopard frogs as a function of seasonal water availability between 1996 and 2011 in the Rincon Mountains, Arizona, USA.

<p>Predicted number of recruits into the adult stage class for an average-sized pool complex (A) and monthly survival (B) with 95% confidence intervals. We made predictions from a model of recruitment as a function of season, seasonal water availability, number of pools per complex, and connectivity, and a model of survival as a function of season and seasonal water availability (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0125670#pone.0125670.t002" target="_blank">Table 2</a>). To predict the number of recruits, we held the number of pools per complex and connectivity values at the mean observed across all pool complexes (5 and 0.24, respectively).</p

Detection probabilities of adult lowland leopard frogs as a function of survey-specific water availability between 1996 and 2011 in the Rincon Mountains, Arizona, USA.

<p>Shaded areas represent 95% confidence intervals. We made predictions from a model of detection probability as a function of effort, survey-specific water availability, and date (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0125670#pone.0125670.t002" target="_blank">Table 2</a>). We predicted detection probability for the midpoint of spring and fall sampling periods (approximately 7 June and 31 Oct) when observers surveyed pool complexes in their entirety (i.e., effort = 1).</p