The U.S. Fish and Wildlife Service listed Anaxyrus canorus, the Yosemite toad, as federally threatened in 2014 based upon reported population declines and vulnerability to global-change factors. A. canorus lives only in California’s central Sierra Nevada at medium to sub-alpine elevations. Lands throughout its range are protected from development, but climate and other global-change factors potentially can limit populations. A. canorus reproduces in ultra-shallow wetlands that typically hydrate seasonally via melting of the winter snowpack. Lesser snowpacks in drier years can render wetland water volumes and hydroperiods insufficient to allow for successful breeding and reproduction. Additionally, breeding and embryogenesis occur very soon after wetlands thaw when overnight temperatures can be below freezing. Diseases, such as chytridiomycosis, which recently decimated regional populations of ranid species, also might cause declines of A. canorus populations. However, reported studies focused on whether climate interacts with any pathogens to affect fitness in A. canorus have been scarce. We investigated effects of these factors on A. canorus near Tioga Pass from 1996 to 2001. We found breeding subpopulations were distributed widely but inconsistently among potentially suitable wetlands and frequently consisted of small numbers of adults. We occasionally observed small but not alarming numbers of dead adults at breeding sites. In contrast, embryo mortality often was notably high, with the majority of embryos dead in some egg masses while mortality among coincidental Pseudacris regilla (Pacific treefrog) embryos in deeper water was lower. After sampling and experimentation, we concluded that freezing killed A. canorus embryos, especially near the tops of egg masses, which enabled Saprolegnia diclina (a water mold [Oomycota]) to infect and then spread through egg masses and kill more embryos, often in conjunction with predatory flatworms (Turbellaria spp.). We also concluded exposure to ultraviolet-B radiation did not play a role. Based upon our assessments of daily minimum temperatures recorded around snow-off during years before and after our field study, the freezing potential we observed at field sites during embryogenesis might have been commonplace beyond the years of our field study. However, interactions among snow quantity, the timing of snow-off, and coincidental air temperatures that determine such freezing potential make projections of future conditions highly uncertain, despite overall warming trends. Our results describe important effects from ongoing threats to the fitness and abundance of A. canorus via reduced reproduction success and demonstrate how climate conditions can exacerbate effects from pathogens to threaten the persistence of amphibian populations.

根据报告的人口下降和对全球变化因素的脆弱性，美国鱼类和野生动物服务局在2014年将优胜美地蟾蜍（Anyyyus toad）命名为Anaxyrus canorus。阿诺斯犬仅生活在加利福尼亚中部内华达山脉中高海拔地区。其整个范围内的土地都受到发展的保护，但是气候和其他全球变化因素可能会限制人口。金丝雀在超浅的湿地中繁殖，这些湿地通常通过冬季积雪融化而季节性地补水。较干燥年份的积雪较少，会使湿地的水量和水文期不足，无法成功繁殖和繁殖。另外，湿地融化后不久，当过夜温度可能低于冰点时，繁殖和胚胎发生就会很快发生。疾病，如壶菌病，最近抽取ranid物种种群的区域，也可能导致的下跌A. canorus人群。然而，报道的研究集中在气候是否与任何病原体相互作用以影响金黄色葡萄球菌的适应性方面，这是很少的。我们调查了这些因素对A. canorus的影响从1996年到2001年，在Tioga Pass附近。我们发现繁殖亚种群分布广泛，但在可能合适的湿地之间不一致，并且通常由少量成年组成。我们偶尔在繁殖地点观察到少量但不令人震惊的成年死亡成年人。相比之下，胚胎死亡率通常很高，大多数胚胎死于某些卵团，而在较深水域中，巧合的Pseudacris regilla（Pacific treefrog）胚胎的死亡率较低。经过采样和实验后，我们得出结论，冷冻杀死了A. canorus胚胎，尤其是在卵团顶部附近，这使腐烂腐烂菌（水霉菌）感染，然后在卵团中传播并杀死更多的胚胎，通常与掠食性扁虫（Turbellaria spp。）结合使用。我们还得出结论，暴露于紫外线B辐射没有作用。根据我们对田间研究前后几年中降雪周围记录的每日最低温度的评估，在我们多年的田野研究之后，我们在胚胎发生期间在田间场所观察到的冻结潜力可能是司空见惯的。然而，尽管总体变暖趋势，降雪量，降雪时间和决定这种冻结潜力的巧合气温之间的相互作用使得对未来状况的预测高度不确定。我们的结果描述了持续威胁健康和丰富度的重要影响。通过降低繁殖成功率的金黄色葡萄球菌，并证明气候条件如何加剧病原体的影响，威胁到两栖动物种群的持久性。