Anaxyrus canorus

The genus Anaxyrus was split from Bufo by Frost et al. (2006). However, taxonomy within the genus Bufo remains controversial and many references still use the long-established Bufo.

"Stephens (2001) examined mitochondrial DNA from 8 Yosemite toads (selected from the samples examined by Shaffer et al. (2000) to represent the range of variability found in that study) and 173 western toads. Stephens' data indicate that Bufo (now Anaxyrus) in the Sierra Nevada occur in northern and southern evolutionary groups, each of which include both Yosemite and western toads (i.e., toads of both species are more closely related to each other within a group than they are to members of their own species in the other group). Further genetic analysis of Yosemite toads sampled from throughout their range, and from other toad species surrounding their range is needed to fully understand the evolutionary history and appropriate taxonomic status of the Yosemite toad (Stephens 2001)." (USFWS 2002).

Molecular data indicate that Anaxyrus exsul is phylogenetically nested within Anaxyrus canorus; further data are needed to determine whether Anaxyrus exsul should be subsumed with Anaxyrus canorus (Shaffer et al. 2000).

Phylogenetic analyses of mtDNA data from throughout the range of the Anaxyrus boreas species group (including boreas, canorus, exsul, and nelsoni) by Goebel et al. (2009) identified three major haplotype clades. The Northwest clade (NW) includes both subspecies of boreas (boreas and halophilus) and divergent minor clades in the middle Rocky Mountains, coastal, and central regions of the west and Pacific Northwest. The Southwest (SW) clade includes exsul, nelsoni, and minor clades in southern California. Anaxyrus canorus, previously identified as paraphyletic, has populations in both the NW and SW major clades. The Eastern major clade (E) includes three divergent lineages from southern Utah, the southern Rocky Mountains, and north of the Great Basin at the border of Utah and Nevada. Goebel et al. (2009) tentatively suggested that some or many of the clades might warrant recognition as distinct species. However, the authors refrained from delineating new species circumscriptions, noting that additional research might suggest different taxonomic outcomes (e.g., recognizing the traditionally defined Anaxyrus canorus as two distinct species or, conversely, combining it with other minor groups and thus broadening its scope).

Yosemite toad populations have exhibited significant historical declines and continue to decline today. Management of grazing activities, a reduction in legacy logging effects, and mountain meadow restoration likely benefit some populations. Climate change is already affecting this species and these effects will likely intensify in the future.

This species is endemic to California, USA. It occurs above 6,500 feet in the central Sierra Nevada mountains between the Lake Tahoe Basin (Blue Lakes (Alpine County California)) in the north to the headwaters of the Kings River in the vicinity of the Evolution Lakes, Fresno County, California (Thompson et al. 2016). Based on analysis of location information derived from California Natural Diversity Database (CNDDB) element occurrences, the range extent of the Yosemite toad is about 10,000 km2.

Given the high potential for the Yosemite toad exhibiting a metapopulation structure (Brown et al 2015) with site occupancy varying over time and space, there may be between 180-200 occurrences in a given year (CNDDB 2021).

Yosemite toad populations are impacted by a series of current threats with varying degrees of severity including outbreaks of chytridiomycosis, caused by infections of the skin in amphibians by Batrachochytrium dendrobatidis and Batrachochytrium salamandrivorans , which has been detected in Yosemite toads (Browne et al 2015), excessive livestock grazing (prevalent in some parts of the Yosemite toad range), intensive recreational (hiking, backpacking, and horseback excursions), and the short-term impacts of vegetation and fuels management actions which most often realized in lower elevation populations and can result in direct mortality of Yosemite toads and reductions in vegetation may impact prey species availability. Legacy timber harvest effects and succession in mountain meadows are localized but severe and reduce overall habitat quality for Yosemite toads. Finally, climate change affects the timing and availability of surface waters, potentially disrupting reproduction timing, and likely negatively affects the abundance and availability of prey species.