Yosemite toad
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The Yosemite toad (''Anaxyrus canorus'', formerly ''Bufo canorus'') is a species of true toad in the family
Bufonidae {{Cat main, Toad This category contains both species commonly called toads, and the true toads from the family Bufonidae {{Cat main, Toad This category Category, plural categories, may refer to: Philosophy and general uses *Categorization, cat ...
.
Endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...
to the
Sierra Nevada The Sierra Nevada () is a mountain range in the Western United States, between the Central Valley of California and the Great Basin. The vast majority of the range lies in the state of California, although the Carson Range spur lies primar ...
of California, the species ranges from the
Alpine County , other_name = , settlement_type = County , image_skyline = , image_flag = Flag of Alpine County, California.svg , flag_size = , image_seal = Seal of Alpine Co ...
to
Fresno County Fresno County (), officially the County of Fresno, is a county located in the central portion of the U.S. state of California. As of the 2020 Census, the population was 1,008,654. The county seat is Fresno, the fifth-most populous city in Cali ...
. Yosemite toads are only found in the montane to subalpine elevational zone of asl. The Yosemite toad is similar to the nearby
Western toad The western toad (''Anaxyrus boreas'') is a large toad species, between long, native to western North America. ''A. boreas'' is frequently encountered during the wet season on roads, or near water at other times. It can jump a considerable distan ...
, but in many ways adapted to a high elevation lifestyle. It was initially described during the Grinnell Survey of California, by an undergraduate student of
Joseph Grinnell Joseph Grinnell (February 27, 1877 – May 29, 1939) was an American field biologist and zoologist. He made extensive studies of the fauna of California, and is credited with introducing a method of recording precise field observations known as ...
named
Charles Camp Charles Lewis Camp (March 12, 1893 Jamestown, North Dakota – August 14, 1975 San Jose, California) was a palaeontologist and zoologist, working from the University of California, Berkeley. He took part in excavations at the 'Placerias Quarry', in ...
.


Description


Adults

Yosemite toads are medium-sized (48–84 mm SVL) stocky
toads Toad is a common name for certain frogs, especially of the family Bufonidae, that are characterized by dry, leathery skin, short legs, and large bumps covering the parotoid glands. A distinction between frogs and toads is not made in scienti ...
, with females averaging larger than males. They generally lack cranial crests, but males will rarely have weakly developed ones. Their eyes have a dark brown iris with gold iridophores. In comparison with the closely related Western toad (''A. boreas''), the parotoid glands are large, narrowly spaced, and irregularly shaped (oval or flattened), less than one gland width apart. Like the parotoids, the eyes are spaced narrowly apart, usually less than the width of the upper eyelid. The warts are large, smooth, and the dorsal skin between warts is smooth as compared to the
Western toad The western toad (''Anaxyrus boreas'') is a large toad species, between long, native to western North America. ''A. boreas'' is frequently encountered during the wet season on roads, or near water at other times. It can jump a considerable distan ...
. It is the most
sexually dichromatic Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...
species of anuran in North America, with males and females displaying strikingly divergent patterns and coloration at maturity. Females are dorsally covered in black blotches that have white or cream borders, with a tan, copper, or ruddy background; males are more uniformly colored, ranging from yellow-green, to olive drab, to greenish brown, sometimes with scattered black flecks near warts. Juveniles resemble adult females, except with a thin mid-dorsal stripe, which gradually fades during development (faster in males than females). A prominent mid-dorsal stripe is lacking in this species, unlike the
Western toad The western toad (''Anaxyrus boreas'') is a large toad species, between long, native to western North America. ''A. boreas'' is frequently encountered during the wet season on roads, or near water at other times. It can jump a considerable distan ...
. As juvenile males mature, their black blotches shrink and ultimately disappear, whereas they expand and reticulate in developing females. Unlike other members of the ''A. boreas'' species group ('' A. boreas, A. nelsoni, A. nestor'' xtinct', A. canorus,'' and '' A. exsul''), Yosemite toad males have a vocal sac and produce an advertisement call to attract females during breeding. The call is a high-pitched, melodious, flute-like trill repeated frequently. Charles Camp chose the specific epithet "canorus" (meaning tuneful) for the species based on its advertisement call. The trill contains 26–51 evenly spaced notes that last an average of 2.6 seconds.


Eggs

Eggs are darkly pigmented and laid in 1 or 2 strands (1 per ovary, the oviducts fuse just before the cloaca in toads), however egg masses may fold during deposition into radiating clusters 4–5 eggs wide. 1000–2000 eggs beaded in two envelopes are laid by females in shallow pools, tangled in vegetation. Individual eggs are 2.1 mm wide on average, and 4.1 mm including the two envelopes.


Tadpoles

Tadpole A tadpole is the larval stage in the biological life cycle of an amphibian. Most tadpoles are fully aquatic, though some species of amphibians have tadpoles that are terrestrial. Tadpoles have some fish-like features that may not be found ...
s are 10–37mm TL and jet black throughout, and hence the intestines are not visible ventrally. Their eyes are set dorsally (in contrast to the co-occurring Sierra chorus frog, which has eyes on the outline of the head when viewed from above). In contrast to the
Western toad The western toad (''Anaxyrus boreas'') is a large toad species, between long, native to western North America. ''A. boreas'' is frequently encountered during the wet season on roads, or near water at other times. It can jump a considerable distan ...
, the snout is shorter and blunted in lateral view, the tail fins are mostly opaque, the tail is deepest about halfway down its length, and the tail tip is more rounded. The labial tooth row formula is 2/3 (2 upper and 3 lower labial tooth rows), and the ratio of lengths of the last 2 rows is 1.6 (in
Western toad The western toad (''Anaxyrus boreas'') is a large toad species, between long, native to western North America. ''A. boreas'' is frequently encountered during the wet season on roads, or near water at other times. It can jump a considerable distan ...
s it is 1.2).


Subadults

Metamorphs (recently metamorphosed tadpoles) are highly pigmented like tadpoles, and quite small, usually 9–14 mm SVL. Juveniles (1+ years in age) reach sexual maturity after 3–5 years (males) or 4–6 years (females), at which time sex-specific colors and patterns emerge. Until then, juveniles resemble adult females: they have a background color varying from brown to grey with generally unconnected black blotches encircling the warts. Unlike adult females, juveniles have a thin mid-dorsal stripe that is white or cream-colored, and orange tubercles on the undersides of their hands and feet. As juveniles mature, their black blotches expand and interconnect if they are females, or shrink if they are males, and the mid-dorsal stripe shrinks and mostly disappears.


Natural history


Breeding

Yosemite toads are explosive breeders (breeds within a short time period), migrating to breeding pools and flooded areas in late spring while snowbanks still veil the frozen meadows. They have been termed the "toad that stays on its toes" or "tiptoeing toad" due to their habit of crossing snowdrifts without touching their abdomen to the cold snow. Breeding time varies greatly with elevation and yearly snowpack (April to July), and depends on timing of snowmelt. Males arrive to breeding ponds synchronously when the meadow is ca. 50% covered in snow. Depending on the population density they will either join a breeding chorus by making an advertisement call to females, or will actively search for them. Their vocalization is a high-pitched, sonorous trill lasting an average of 2.6 seconds and repeated frequently. Males intermittently call from pool margins, under logs, or inside willows to attract females. When females arrive, they are immediately grasped in
amplexus Amplexus (Latin "embrace") is a type of mating behavior exhibited by some externally fertilizing species (chiefly amphibians and horseshoe crabs) in which a male grasps a female with his front legs as part of the mating process, and at the same ...
by one or multiple males as the males fight for a limited number of mating opportunities. Breeding sex ratios can be very skewed toward males since females breed less frequently than males, although both sexes typically do not breed in consecutive years. While in amplexus, females will lay one clutch of 1,000–2,000 eggs. Eggs hatch after 1–2 weeks, and the length of time depends heavily on ambient temperature and fluctuations in temperature. Females generally breed once and leave after 2–3 days, while males remain for 1–2 weeks.


Habitat use

The species primarily uses
montane Montane ecosystems are found on the slopes of mountains. The alpine climate in these regions strongly affects the ecosystem because temperatures fall as elevation increases, causing the ecosystem to stratify. This stratification is a crucial ...
and subalpine wet meadows for breeding, but will occasionally breed in ephemeral ponds, lake margins, or other riparian areas. Flatter, southwesterly meadows, with more precipitation, containing warmer waters seem to be favored by the species. More specifically, breeding takes place in shallow snowmelt ponds or flooded areas, and eggs are usually deposited in water less than 5 cm deep. Shallow water makes eggs vulnerable to freezing, because nighttime temperatures are particularly low during springtime snow melt off. Females will sometimes split their clutch into multiple areas, or deposit their clutch communally with other pairs in a single area. The relatively large amount of pigmentation in eggs and tadpoles is thought to help expedite development, and tadpoles will congregate in the shallowest, warmest margins of ponds during the day. At nighttime tadpoles settle down into the silty detritus where they are more insulated from the cold nighttime temperatures. This often gives their pools the appearance of "golf ball" texture, because tadpoles leave divots in the silt (see picture of breeding pool). It is not uncommon for a large number of breeding ponds to desiccate each season before tadpoles successfully metamorphose, hence there is apparently a selective tradeoff between shallow ponds (which accelerate tadpole development) and ponds with long hydroperiods (which ensure survival). Time from hatching to tadpole metamorphosis is 4–6 weeks, and this is highly dependent upon environmental factors (elevation, weather, food, competition) and possibly genetic background. Tadpoles are apparently unable to overwinter. Subadult and adult habitat use patterns are poorly understood. Metamorphs appear to move away from breeding ponds soon after transformation, however they probably overwinter nearby in stream channels and associated vegetation (willows, sedges, and grasses). Many juveniles (1+ years in age) probably disperse farther upland into adult foraging habitat, especially by mid-summer of their second year, but they can also be found nearby breeding ponds. Adult upland foraging habitat tends to be covered in seeps and springs, willows, tall forbs, granitic boulders, or (at lower elevation) forest clearings. Rodent burrows play an essential role in providing shelter from predation and weather, as do willows, logs, and rocks. Overwintering habitat is also includes the burrows of rodents such as
pocket gophers Pocket gophers, commonly referred to simply as gophers, are burrowing rodents of the family Geomyidae. The roughly 41 speciesSearch results for "Geomyidae" on thASM Mammal Diversity Database are all endemic to North and Central America. They are ...
,
vole Voles are small rodents that are relatives of lemmings and hamsters, but with a stouter body; a longer, hairy tail; a slightly rounder head; smaller eyes and ears; and differently formed molars (high-crowned with angular cusps instead of lo ...
s, and
Belding's ground squirrel Belding's ground squirrel (''Urocitellus beldingi''), also called pot gut, sage rat or picket-pin, is a squirrel that lives on mountains in the western United States. In California, it often is found at in meadows between Lake Tahoe Lake Ta ...
s, along with willow root tangles, which all probably keep an optimal thermal and mesic environmental for hibernating toads.


Movement patterns

Yosemite toads show high site fidelity to both breeding and upland foraging habitat, often using the same breeding pools and refuges in subsequent years. After breeding, adults forage in upland riparian areas of the breeding meadows, or (less commonly) disperse into the surrounding forest or subalpine environmental matrix. Although adult toads are capable of significant dispersal away from breeding pools, they are generally found within 90 m of permanent water; occasionally they are found in xeric forest habitat. Female toads disperse farther than males, and have been found to move up to 1.26 kilometers from their breeding grounds in one season.Liang, C.T. 2010. Habitat modeling and movements of the Yosemite toad (Anaxyrus (=Bufo) canorus) in the Sierra Nevada, California. PhD Dissertation, University of California, Davis. (September) 126 pp. However, dispersal between meadows appears to be very low, estimated to be about 2% between 400 m meadows.


Hibernation

This is possibly due to unfavorably dry habitat between meadow complexes. Overwintering sites are rodent burrows or willow thickets (see "Habitat Utilization"), and the first freezing nighttime temperatures seem to cue adult toads to seek hibernacula. Hibernation usually begins in the late summer or early fall, between September and October.


Feeding

Like other toads, Yosemite toads are ambush predators. They lunge at prey and open their mandibles, causing their sticky tongue to unfold, flip downward, and pull the animal into their mouths. Adult stomach contents have included: tenebrionid beetles, ladybird beetles,
weevil Weevils are beetles belonging to the superfamily Curculionoidea, known for their elongated snouts. They are usually small, less than in length, and herbivorous. Approximately 97,000 species of weevils are known. They belong to several families, ...
s, craneflies,
mosquito Mosquitoes (or mosquitos) are members of a group of almost 3,600 species of small flies within the family Culicidae (from the Latin ''culex'' meaning " gnat"). The word "mosquito" (formed by ''mosca'' and diminutive ''-ito'') is Spanish for "li ...
s, caterpillars,
carpenter ant Carpenter ants (''Camponotus'' spp.) are large () ants indigenous to many forested parts of the world. They build nests inside wood consisting of galleries chewed out with their mandibles or jaws, preferably in dead, damp wood. However, unl ...
s, dragonfly naiads, centipedes, julid millipedes, and spiders. Juvenile stomach contents have included:
ant Ants are eusocial insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from vespoid wasp ancestors in the Cretaceous period. More than 13,800 of an estimated total of ...
s, spiders, and
wasp A wasp is any insect of the narrow-waisted suborder Apocrita of the order Hymenoptera which is neither a bee nor an ant; this excludes the broad-waisted sawflies (Symphyta), which look somewhat like wasps, but are in a separate suborder. ...
s. Metamorph stomach contents have included: owl flies,
flies Flies are insects of the order Diptera, the name being derived from the Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advanced m ...
,
springtail Springtails (Collembola) form the largest of the three lineages of modern hexapods that are no longer considered insects (the other two are the Protura and Diplura). Although the three orders are sometimes grouped together in a class called Ento ...
s, spider mites, and spiders. There appears to be an ontogenetic shift from eating mostly spider mites (metamorphs), to eating a mix of spider mites, spiders, and tiny wasps (2 months post-metamorphosis), to eating mostly larger hymenopterans, mostly
ant Ants are eusocial insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from vespoid wasp ancestors in the Cretaceous period. More than 13,800 of an estimated total of ...
s (juveniles), to eating 80% hymenopterans, consisting of bees and
wasp A wasp is any insect of the narrow-waisted suborder Apocrita of the order Hymenoptera which is neither a bee nor an ant; this excludes the broad-waisted sawflies (Symphyta), which look somewhat like wasps, but are in a separate suborder. ...
(adults). Tadpoles are grazers on detritus and algae, however it remains unclear whether they ingest those items, bacteria, rotifers, or something else. Tadpoles are also known to opportunistically scavenge conspecific tadpoles, Sierra chorus frog tadpoles,
Belding's ground squirrel Belding's ground squirrel (''Urocitellus beldingi''), also called pot gut, sage rat or picket-pin, is a squirrel that lives on mountains in the western United States. In California, it often is found at in meadows between Lake Tahoe Lake Ta ...
s, and predaceous diving beetle larvae, as well as graze on
lodgepole pine ''Pinus contorta'', with the common names lodgepole pine and shore pine, and also known as twisted pine, and contorta pine, is a common tree in western North America. It is common near the ocean shore and in dry montane forests to the subalpin ...
pollen grains.


Adaptations to high elevation

Yosemite toads have several apparent adaptations to high elevation. Males live to be at least 12 years, and females until at least 15 years. Their longevity probably helps them outlast years of low snowpack that cause poor breeding conditions, and thus low metamorphic recruitment. They are largely diurnal in contrast to the majority of anurans, probably owing to the cold mountain temperatures. Aligning their activities with diel peaks in warmth allows them to absorb solar energy to catch and biosynthesize food. The high level of melanism in eggs and tadpoles (and possibly in adult females), as well as the tendency for tadpoles to congregate in the warm shallows, probably serves the same purpose. Similarly, the selection of shallow breeding sites by adults, and shallow water margins by tadpoles, probably reflects the intense pressure to metamorphose in a short season, and hence the importance of using high temperature for rapid development. The marked dichromatism between males and females is still an evolutionary mystery. One possible explanation sexual selection. Females could be sexually selecting for lighter coloration in males, as some kind of proxy for male fitness, or males could be signaling their maleness to attract females and ward off over-zealous males. Males of the Yosemite toad and many other bufonid species change into a lighter color during breeding (e.g.
Western toad The western toad (''Anaxyrus boreas'') is a large toad species, between long, native to western North America. ''A. boreas'' is frequently encountered during the wet season on roads, or near water at other times. It can jump a considerable distan ...
s,
American toad The American toad (''Anaxyrus americanus'') is a common species of toad found throughout Canada and the eastern United States. It is divided into three subspecies: the eastern American toad (''A. a. americanus''), the dwarf American toad (''A. a ...
s), and other notable high elevation bufonids outside North America are highly sexually dichromatic (e.g. golden toads, yellow toads, marbled toads). Another more likely hypothesis is that males and females occupy largely different habitats, and evolution has de-coupled
camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...
between the sexes. Males spend disproportionately more time in shallow, brown, silty breeding ponds, where they are highly exposed to predators. In contrast, females quickly leave pond habitat for rocky upland habitat where
disruptive coloration Disruptive coloration (also known as disruptive camouflage or disruptive patterning) is a form of camouflage that works by breaking up the outlines of an animal, soldier or military vehicle with a strongly contrasting pattern. It is often comb ...
may be more suitable. More than 60% of adults toads found in upland habitat during the late summer are females, whereas less than 10% are males. In lowland breeding habitat, this pattern is reversed: 54% of adult toads are males, and only 19% are females. Regardless of which hypothesis is correct, their diurnal habits make color and pattern subject to increased selection.


Lineage diversification and fusion

Karlstrom was the first to hypothesize, based on the distribution of ''A. canorus'' in Yosemite National Park, that glaciers had helped the species differentiate from ''A. boreas''. The idea was that repeated glacial action had helped isolate the species in montane areas, and gradual adaptation there had helped it competitively exclude ''A. boreas'' from high elevation terrain. Recent work has showed this is likely true, and part of a larger pattern of glacial action bifurcating the species into new lineages. The species likely originated in the early Pleistocene, and many of the glacial cycles since then have isolated toads into western and eastern refugia; here they have adapted to different climatic conditions, reinforcing the formation of new lineages. Where the lineages came back into secondary contact, they occasionally fused into additional hybrid lineages, in cases where pre-post-zygotic barriers were low enough to allow hybridization, but high enough to allow hybrids to become distinct from parental types. Four distinct lineages were discovered in Yosemite National Park, in addition to three fused (hybrid) lineages; two lineages were also found in Kings Canyon National Park.


Conservation

Yosemite toads are reported to have declined substantially in distribution and abundance across their restricted range. Although threats to persistence of the species are less understood than in other California amphibians such as the Sierra Nevada yellow-legged frog, the two most significant appear to be drought (increasing with
climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
) and disease (primarily
chytridiomycosis Chytridiomycosis ( ) is an infectious disease in amphibians, caused by the chytrid fungi '' Batrachochytrium dendrobatidis'' and '' Batrachochytrium salamandrivorans''. Chytridiomycosis has been linked to dramatic population declines or extinc ...
). Interactions between the two are not well understood. The species is listed as "Vulnerable" by the International Union for Conservation of Nature ( IUCN), "Threatened" by the US Fish & Wildlife Service (
USFWS The United States Fish and Wildlife Service (USFWS or FWS) is an agency within the United States Department of the Interior dedicated to the management of fish, wildlife, and natural habitats. The mission of the agency is "working with othe ...
) under the
ESA , owners = , headquarters = Paris, Île-de-France, France , coordinates = , spaceport = Guiana Space Centre , seal = File:ESA emblem seal.png , seal_size = 130px , image = Views in the Main Control Room (120 ...
, and " California species of special concern" by the California Department of Fish & Wildlife ( CDFW).


Systematics


References


External links


California Herps GuideAmphibiaWeb PagePaul Maier Research on Yosemite toadsUS Fish & Wildlife PageSierra Forest Legacy Page
{{Taxonbar, from=Q302397 Anaxyrus Amphibians described in 1916 Amphibians of the United States Endemic fauna of California Fauna of the Sierra Nevada (United States) Yosemite National Park Taxonomy articles created by Polbot ESA threatened species