|Habitat range of A. americanus|
The American toad (Anaxyrus americanus) is a common species of toad found throughout the eastern United States and Canada. It is divided into three subspecies—the eastern American toad (A. a. americanus), the dwarf American toad (A. a. charlesmithi), and the rare Hudson Bay toad (A. a. copei). A new taxonomy places this species in the genus Anaxyrus instead of Bufo.
The eggs of the American toad are laid in two strings and can hatch in 2-14 days. When hatched the tadpoles are recognizable by their skinny tails in relation to the size of their black bodies. They may advance to adulthood in 50-65 days. When metamorphosis is completed, the "toadlets" may stay in the water for a short period of time before they become mostly land based. Studies have shown that they have a mutualistic relationship with Chlorogonium alga, which makes tadpoles develop faster than normal.
Tadpoles have several mechanisms to reduce predation . They avoid predators by swimming in very shallow water, and by swimming close together in schools during the day. Tadpoles also produce toxic chemicals in their skin that discourage some potential predators. Fish have been reported to die after consuming one tadpole; however, most fish quickly learn to avoid eating American toad tadpoles. The tadpoles are also very small and they are a solid black color.
Based on DNA sequence comparisons, Anaxyrus americanus and other North American species of Anaxyrus are thought to be descended from an invasion of toads from South America prior to the formation of the Isthmus of Panama land bridge, presumably by means of rafting.
Eastern American toad
The eastern American toad (A. a. americanus) is a medium-sized toad usually ranging in size from 5–9 cm (2.0–3.5 in); record 11.1 centimetres (4.4 in). The color and pattern is somewhat variable. Skin color can change depending on humidity, stress, and temperature. Color changes range from yellow to brown to black. Their breeding habits are very similar to Anaxyrus fowleri. The call or voice of a breeding male is a high trill, lasting 6-30 seconds, similar to a ringing telephone. They hibernate during the winter. The eastern American toad has spots that contain only one to two warts. It also has enlarged warts on the tibia or lower leg below the knee. While the belly is usually spotted, it is generally more so on the forward half (in some rare individuals there may be few or no spots). This subspecies of the American toad has no or very little markings on it. The spades on the back legs are blackish. Some toads of this subspecies have red warts on their bodies. Also eastern American toads have parotoid glands that are the same color as the surrounding skin. The glands don't have any patterning on them.
Other species which may be confused with the eastern American toad are Fowler's toad, which has three or more warts in the largest dark spots, and in the far west of its range woodhouse's toad. Fowler's toad can be especially difficult to identify in comparison to the eastern American toad but one difference is that it never has a spotted belly and both cranial crests touch the parotoid glands. In the eastern American toad these crests almost never touch the parotoid glands, which secrete bufotoxin, a poisonous substance. The poison the toad excretes is mild in comparison to other poisonous toads and frogs, but it can irritate human skin and is dangerous to smaller animals (such as dogs) when ingested.
American toads require a semi-permanent freshwater pond or pool with shallow water in which to breed and for their early development. They also require dense patches of vegetation, for cover and hunting grounds. Given these two things and a supply of insects for food, American toads can live almost everywhere, ranging from forests to flat grassland. Adult toads are mostly nocturnal, although juveniles are often abroad by day. These toads commonly seek cover in burrows, under boardwalks, flat stones, boards, logs, wood piles, or other cover. When cold weather comes, these toads dig backwards and bury themselves in the dirt of their summer homes, or they may choose another site in which to hibernate. Their diet includes crickets, mealworms, earthworms, ants, spiders, slugs, centipedes, moths, and other small invertebrates.
The eastern American toad may be confused with the Canadian toad in the area where they overlap, but the cranial crests in the American toad do not join to form a raised "boss" (bump) like they do in the Canadian toad. Its range also overlaps with the southern toad's, but in this species the cranial crests form two unique knobs.
Dwarf American toad
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The dwarf American toad (B. a. charlesmithi), is a smaller version of the American toad which reaches lengths of about 6 cm (2½ inches) and is generally a dark reddish color ranging to light red in some specimens in isolated populations. The spots on the back are reduced or absent, and when present they contain a few small red warts and a black ring around it like in the normal American toad. The warts are always darker than the skin of the toad. Some specimens have a white dorsal line in the middle of their backs. The ventral surface or belly is usually cream colored with a few dark spots in the breast area. This subspecies can be distinguished from the above mentioned species in the same manner as for the eastern American toad. The southwestern portion of the Dwarf American toad's range overlaps with that of the Gulf Coast toad. The latter species is distinguished by the presence of a dark lateral stripe as well as a deep "valley" between its prominent cranial crests. It eats mainly spiders, worms and small insects. This subspecies of the American toad has been seen in the northern parts of Ontario were there are a few isolated populations. Interbreeding with the normal and eastern American toads caused this subspecies to lose the red coloring on their backs. These northern dwarf toads mostly have the red coloring on the sides of their bodies and have an unusually high number of warts for the subspecies.
Hudson Bay toad
The Hudson Bay toad (A. a. copei) is a rare Canadian subspecies of A. americanus.
- Geoffrey Hammerson (2004). "Anaxyrus americanus". IUCN Red List of Threatened Species. Version 2011.2. International Union for Conservation of Nature. Retrieved 18 December 2011.
- Frost, D. R.; Grant, T.; Faivovich, J. N.; Bain, R. H.; Haas, A.; Haddad, C. L. F. B.; De Sá, R. O.; Channing, A.; Wilkinson, M.; Donnellan, S. C.; Raxworthy, C. J.; Campbell, J. A.; Blotto, B. L.; Moler, P.; Drewes, R. C.; Nussbaum, R. A.; Lynch, J. D.; Green, D. M.; Wheeler, W. C. (2006). "The Amphibian Tree of Life". Bulletin of the American Museum of Natural History 297: 1–291. doi:10.1206/0003-0090(2006)297[0001:TATOL]2.0.CO;2. hdl:2246/5781.
- Review: The Amphibian Tree of Life, by Frost, D.R. et al., Amphibiatree
- "ADW: Bufo americanus: Information". Animaldiversity.ummz.umich.edu. Retrieved 2011-04-01.
- "University of Notre Dame: Yellow perch predation on tadpoles" (PDF). Retrieved 2011-04-01.
- Pauly, G. B; Hillis, D. M.; Cannatella, D. C. (November 2004). "The history of a Nearctic colonization: Molecular phylogenetics and biogeography of the Nearctic toads (Bufo)". Evolution 58 (11): 2517–2535. doi:10.1111/j.0014-3820.2004.tb00881.x. Retrieved 2011-12-18.
- American toad (Bufo americanus), Natural Resources Canada
- Conant, Roger (1975). A Field Guide to Reptiles and Amphibians of Eastern and Central North America. Boston: Houghton Mifflin. ISBN 0-395-19979-4.
- American toad, FrogWatch
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