There are many iconic amphibian species around the world, and when they disappear, people notice. The Yosemite toad (Anaxyrus canorus) is endemic to California’s Sierra Nevada mountains, and suffered mass die-offs in the late 1970s. Dodge et al (2024) investigated the historical and contemporary effects of Batrachochytrium dendrobatidis (Bd), which causes a fatal amphibian disease called chytridiomycosis on the Yosemite toad. When global amphibian declines were first noticed in the 1970s and 1980s, it was decades before Bd was discovered (1998). This study used a retrospective analysis to determine Bd presence/absence on 719 museum specimens collected between 1915 and 2005, and on an additional 1,678 samples collected from live animals in the wild (2004–2012). Their study found that: 1) Bd emerged coincident with historical declines; 2) Bd is currently widely distributed throughout the species range; 3) life stage, elevation, and precipitation regime were associated with Bd infection likelihood; and, 4) the juvenile life stage was the most highly infected, with some having Bd infection loads surpassing a mortality threshold identified in other species. Thus, Bd may have played a significant yet unrecognized role in the decline of the Yosemite toad, and may continue to affect survival, recruitment, and extinction risk. These represent key insights for efforts to recover this species across its historical range and may also be important in hundreds of other species that declined before Bd was discovered.

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