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Description

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The European, American, or Plains Spadefoot Toad is a small but rotund toad-like frog, generally resembling true toads (Bufonidae) in body form. Spea bombifrons can grow up to 2¼" in snout-vent length (Colorado Herpetological Society 2002). Its skin, which is relatively smooth, can range from gray to brown, sometimes with a greenish hue, and is scattered with darker spots or blotches. The skin is also smoother and thinner than that of Bufonidae. Along the dorsal and lateral surfaces run four vague light stripes, the middle two of which occasionally resemble an hourglass. There are many small tubercles on the otherwise smooth skin. The ventral surface is white and has no markings, although the throat of the male is bluish or grayish on the sides (USGS 2002). There is a raised, bony lump (boss) between the large eyes. The eye has an elliptical, vertical, cat-like pupil, and thus differs from the true toads, whose pupils are round. S. bombifrons also differs from Bufo in that it has no parotid glands (or, when present, they are indistinct) (USGS 2002). Like the other members of the family Pelobatidae, or the spadefoots, S. bombifrons is named for its large, well-developed, wedge-shaped, sharp-edged, black tubercle or metatarsal "spade" on the bottom of each hind foot. This bony element, which is capped with a keratinous cover, is used to burrow rear-first (USGS 2002).

Substantial population declines observed during extended droughts are more likely a result of non-breeding during suboptimal environmental conditions than true population declines (Cottonwood 1986).

References

  • Alberta Wildlife Management Division (). The Status of Alberta Wildlife. Alberta Environmental Protection, Natural Resources Service, Wildlife Management Division, Edmonton, Alberta.
  • Axys Environmental Consulting Ltd. (). Wildlife Surveys for the Proposed Express Pipeline Project. Prepared for Express Pipeline, a division of Alberta Energy Company Ltd., and TransCanada Pipelines Ltd., Calgary, Alberta.
  • Axys Environmental Consulting Ltd. (). Wildlife Surveys for the Proposed AEC Suffield Gas Pipeline Project. Prepared for Alberta Energy Company Ltd., Calgary, Alberta.
  • Black, J.H. (). ''Amphibians of Montana.'' Montana Wildlife, Animals of Montana, Series , -.
  • Bragg, A.N. (). ''The spadefoot toads in Oklahoma with our summary of our knowledge of the group.'' American Naturalist, , -.
  • Bragg, A.N. (). ''A theory of the origin of spade-footed toads deduced principally by a study of their habits.'' Animal Behaviour, , -.
  • Bragg, A.N. (). ''The spadefoot toads in Oklahoma with our summary of our knowledge of the group: II.'' American Naturalist, , -.
  • Bragg, A.N. (). Gnomes of the Night: the Spadefoot Toads. University of Pennsylvania Press, Philadelphia, PA.
  • Bragg, A.N. (). ''Recent studies on spadefoot toads.'' Bios, , -.
  • Buchholz, D.R. and Hayes, T.B. (). ''Comparative larval biology in spadefoot toads.'' American Zoologist, , A.
  • Collins, J.T. (). Amphibians and Reptiles in Kansas, nd Edition. University of Kansas Museum of Natural History, Lawrence, KS.
  • Colorado Herpetological Society (). ''Plains Spadefoot Toad (Spea bombifrons).'' Guide to the Reptiles and Amphibians of Colorado. Colorado Herpetological Society.
  • Cook, F.R. (). ''New localities for the Plains Spadefoot Toad, Tiger Salamander, and the Great Plains Toad in the Canadian Prairies.'' Copeia, (), -.
  • Cook, F.R. (). ''Additions to the known range of some amphibians and reptiles in Saskatchewan.'' Canadian Field-Naturalist, , -.
  • Cook, F.R. and Hatch, D.R.M. (). ''A spadefoot toad from Manitoba.'' Canadian Field-Naturalist, , -.
  • Corn, P.S. (). ''What we know and don't know about amphibian declines in the West.'' Sustainable Ecological Systems: Implementing an Ecological Approach to Land Management. USDA Forest Service, Fort Collins, CO, -.
  • Cottonwood Consultants (). An Overview of Reptiles and Amphibians in Alberta's Grassland and Parkland Natural Regions. Prepared for the Wild West Program, World Wildlife Fund Canada, Toronto, Ontario.
  • Didiuk, A. (). ''Status of amphibians in Saskatchewan.'' Amphibians in Decline: Canadian Studies of a Global Problem. D.M. Green, eds., Society for the Study of Amphibians and Reptiles, Saint Louis, Missouri, -.
  • Farrar, E.S. and Hey, J.D. (). Plains Spadefoot (Scaphiopus bombifrons) Distribution, Breeding Habitat Characterization, and Natural History Studies in Western Iowa: Studies. Wildlife Diversity Program Grant Report , Boone, IA.
  • Femmer, S.R. (). Distribution and Life History Studies of Scaphiopus bombifrons Cope and Bufo cognatus Say in Missouri. M.A. Thesis, University of Missouri, Columbia, MO.
  • Huggins, D.G. (). ''Scaphiopus bombifrons Cope, a species new to Iowa.'' Journal of Herpetology, (/), .
  • Justus, J.T., Sandomir, M., Urquhart, T., and Ewan, B.O. (). ''Developmental rates of two species of toads from the desert southwest.'' Copeia, (), -.
  • Klassen, M.A. (). ''Observations on the breeding and development of the Plains Spadefoot, Scaphiopus bombifrons, in southern Africa.'' Canadian Field-Naturalist, , -.
  • Landreth, H.F. and Christensen, M.T. (). ''Orientation of the Plains Spadefoot Toad, Spea bombifrons, to Solar Cues.'' Herpetologica, , -.
  • Lauzon, R.D. (). ''Status of the Plains Spadefoot (Spea bombifrons) in Alberta.'' Wildlife Status Report No. . Alberta Environment, Fisheries, and Wildlife Management Division, and Alberta Conservation Association, Edmonton, Alberta..
  • Lauzon, R.D. and Balagus, P. (). ''New Records from the Northern Range of the Plains Spadefoot Toad, Spea bombifrons, in Alberta.'' Can. Field-Nat., , -.
  • Nature Conservancy (). The Natural Heritage Network.
  • Pearson, P.G. (). ''Population ecology of the spadefoot toad, Scaphiopus h. holbrooki (Harlan).'' Ecological Monographs, (), -.
  • Preston, W.B. and Hatch, D.R.M. (). ''The Plains Spadefoot, Scaphiopus bombifrons, in Manitoba.'' Canadian Field-Naturalist, (), -.
  • Ruibal, R., Tevis, L., Jr, and Roig, V. (). ''The terrestrial ecology of the spadefoot toad Scaphiopus hammondii.'' Copeia, (), -.
  • Russell, A.P. and Bauer, A.M. (). The Amphibians and Reptiles of Alberta. University of Calgary Press, Calgary, Alberta.
  • United States Geological Service (). Plains Spadefoot, Spea bombifrons. USGS: Northern Prairie Wildlife Research Center, Jamestown, ND.

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Distribution and Habitat

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Spea bombifrons is native to the more arid Plains region of western North America: the plains east of the Rocky Mountains from southern Alberta, Manitoba, and Saskatchewan to northwest Texas and Chihuahua, Mexico, east to Missouri and eastern Oklahoma and into eastern Arizona, with isolated populations in south Texas and Mexico (Stebbins 1985).

Throughout the majority of its range, the distribution S. bombifrons is highly correlated with sandy, gravelly, or sandy loam soils, but it ranges from deserts in the American Southwest to aspen parkland in the Canadian prairies(Bragg 1944; Cook 1960; Black 1970; Huggins 1971; Femmer 1978; Collins 1982; Cook and Hatch 1964; Cottonwood Consultants 1986). S. bombifrons has been found in unvegetated sand dunes, sand dunes with willow and cottonwood, upland prairie, desert, short and mixedgrass prairie, mixed shrubland, fescue grassland, floodplains, and sagebrush (Bragg 1944; Black 1970; Huggins 1971; Stebbins 1985; Axys 1996 and 1997). East of the Rockies, S. bombifrons is found in shortgrass prairie and desert grasslands, where the soil is loose (USGS 2002).

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Life History, Abundance, Activity, and Special Behaviors

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The habitat, breeding season, and breeding location are highly related. S. bombifrons is nocturnal, and spends most of its time underground, emerging only to breed in favorable moist conditions, or to feed (Lauzon 1999). During extended droughts, the frog does not remain underground indefinitely but emerges, especially during humid weather, to forage during the evening (Bragg 1965; Ruibal 1969). S. bombifrons burrows deeper into the soil and emerges less frequently as the summer progresses and the soil dries (Bragg 1965). It prefers loose soil, where it can easily burrow with the aid of its “spades” up to depths of almost 1 m (Baxter & Stone 1980; Russell & Bauer 1993; USGS 2002). They will most often burrow along the edge of a solid object or near a plant that provides security or shade (Bragg 1944). During the winter, it burrows deeply to avoid freezing and desiccation, as S. bombifrons does not tolerate freezing and must burrow below the frost line (Baxter & Stone 1980). This spadefoot toad surfaces quickly from its burrow and opportunistically migrates to breeding wetlands during periods of heavy rainfall and warm temperatures (Bragg 1965; Klassen 1998; Lauzon & Balagus 1998). The measured amount of rainfall required for emergence varies from 2.5 to 10.4 cm (Black 1970; Femmer 1978; Farrar & Hey 1995).

Large choruses of these frogs have been associated with heavy rainfall, but the temporary wetlands that result from light rain or snow melt are known to attract small choruses as well (Lauzon 1999). S. bombifrons has been observed calling when daily maximum temperatures were 12.5°C to 23.5° and daily minimum temperatures were 7°C to 10.5°C (Klassen 1998), although breeding frogs have been observed in the southeastern extreme of their range at temperatures as low as 9°C (Bragg 1965). S. bombifrons has been observed calling at water temperatures of 10.5°C to 16°C (Lauzon 1999).

No studies have been conducted on the home range of S. bombifrons, but the related Eastern Spadefoot (Spea holbrooki holbrooki) has an average home range of 10.1 m2, with male home ranges generally larger than those of the female (Pearson 1955). S. bombifrons is known to be capable of migrating at least 1.6 km to breeding sites, and juveniles have been found more than 2 km from known breeding wetlands within weeks of metamorphosis (Landreth & Christensen 1971; Klassen 1998). This frog forages above ground, and its prey are a variety of insects (Lauzon 1999). In Oklahoma, this included flies, hymenopterans, moths, beetles, pentatomids, and various spiders (Bragg 1944). S. bombifrons is generally active from the start of its breeding season until the fall (Lauzon 1999). The breeding season is generally correlated with annual peaks in precipitation. In the center of its range, S. bombifrons breeds from May to August. In the southern end of its range, S. bombifrons breeds in July, after the summer rains. In the northern part, breeding may take place in late May at the earliest. If appropriate environmental conditions do not occur during the active season, breeding may not occur at all; conversely, S. bombifrons may breed more than once in a single year if conditions are particularly conducive (Bragg 1944 & 1965; Klassen 1998).

Spea bombifrons lays its eggs in a variety of wetlands, but prefers flooded areas and temporary pools (USGS 2002). Its preference for sandy soils leaves S. bombifrons with limited breeding opportunities, since the soil drains rapidly and precludes the development of breeding wetlands. As a result, this spadefoot relies on fine-textured, less permeable soils within sandier habitats where temporary wetlands form and it is able to breed (Lauzon 1999). Breeding pond depths vary from 10 cm to more than 1 m. It tolerates varying amounts of vegetation, and native as well as tame habitats (Bragg 1965; Farrar & Hey 1995; Klassen 1998). Spawning S. bombifrons have been observed in partially flooded fields, roadside ditches, flooded dugouts, shallow temporary wetlands in fallow fields, temporary ponds in uplands, along streams, semi-permanent pools, oxbow lakes, stream meander channels, unvegetated sloughs, marshy depressions, flooded cultivated fields, temporary wetlands in pastures, river backwaters, and ditches (Cook 1965; Cottonwood 1986; Preston & Hatch 1986). These frogs have been observed breeding in non-native habitats such as a construction site (Femmer 1978), flooded soybean fields and cornfields (Farrar & Hey 1995), a flooded wheat field, and even driveways and bicycle paths (Didiuk).

This spadefoot breeds quickly to take advantage of its typically ephemeral wetland, and to allow the eggs and larvae as much time as possible to develop. The largest numbers have been observed during or the first night after heavy rains, with counts falling off dramatically thereafter (Bragg 1965). Generally, males migrate to the breeding wetlands before females, and generally outnumber them in a given time and place (Bragg 1945; Baxter & Stone 1980). The call of the male is loud, harsh, and may be heard at distances of up to 3 km (Lauzon 1999). The male spadefoot call greatly stimulates both sexes, and larger choruses attract more individuals of both sexes (Bragg 1945).

Females lay up to 2000 eggs in clutches of 10 to 250 each (Bragg 1965; Collins 1982). Whereas true toads lay their eggs in strings, S. bombifrons females lay eggs in spherical masses, attached to submerged vegetation (Baxter & Stone 1980). Suspended soil particles and other debris adhere to the sticky surface of the egg mass to help camouflage them from predators (Bragg 1965). The rate of egg development is temperature dependent, and under normal conditions spadefoot eggs will hatch in about two days (Bragg 1965). The lethal temperature limits for eggs are <10°C and >34°C (Justus 1977). Spadefoot toads (family Pelobatidae) as a group have the fastest development rate among amphibians (Bragg 1961). Larval development is also temperature dependent and thus allows the tadpoles to develop faster in conditions that evaporate the temporary breeding wetlands (Buchholz & Hayes 1996). In southern regions (in this study, Oklahoma), the time from hatching to metamorphosis may be as little as 14 days (Bragg 1967), with a range of 17 to 20 (in Missouri) days being more common (Femmer 1978); in the north (Alberta), metamorphosis has been observed 21 to 34 days after hatching, with some tadpoles requiring 60 days (Klassen 1998).

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Life History, Abundance, Activity, and Special Behaviors

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There is no evidence to suggest that the range is contracting (Lauzon 1999). The spadefoot toads as a group do not include any declining species (Corn 1994). This amphibian is not included on any list of rare, endangered, threatened, or sensitive species (Nature Conservancy 1999; RedList). The Nature Conservancy assigns S. bombifrons a global rank of G5, indicating that the species is “demonstrably secure” across its global range (Nature Conservancy 1999). The Province of Alberta places S. bombifrons on its Blue List of species that may be at risk of declining to non-viable levels within the Province’s boundaries (Alberta Wildlife Management Division 1996). This species’ highly variable population size, the result of annual variability in the availability of breeding wetlands, is responsible for this designation. The population there is considered stable but moderately threatened due to current land use practices (Lauzon 1999).

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Relation to Humans

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Alteration and destruction of habitat are considered the only possible risk to habitats suitable for S. bombifrons. Availability of wintering and breeding habitats are the likely limiting factors of this amphibian; agriculture is primarily responsible for the loss of prairie land and is probably the most significant threat (Lauzon 1999). Cultivation and drainage of wetlands, as for cattle, as well as flood control, have also been identified as potential threats (Cottonwood 1986).

The extent to which fragmentation of prairie land and other habitats has affected toad movements between populations or the re-colonization of populations sinks is unknown (Didiuk 1997).

Other human activities, such as the widespread use of herbicides and pesticides, oil and gas exploration and development, and road kills have been implicated in the decline of related amphibians and those with similar ranges as S. bombifrons, but none has been studied specifically with regard to this species (Lauzon 1999).

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Behavior

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Plains spadefoot toads have a mating call that is approximately 0.5 - 1.0 second in length and sounds similar to that of a mallard. This call, and another low, rough call, both act as mating calls. A male's mating call can be heard as far as 3 km away.

Communication Channels: tactile ; acoustic

Perception Channels: visual ; tactile ; acoustic ; chemical

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Dewey, T. 2006. "Spea bombifrons" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Spea_bombifrons.html
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Conservation Status

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Plains spadefoot toad populations seem to be healthy, for the most part. Local population declines are often the result of lack of breeding during drought years. In Alberta they are on the "blue list" of species at risk of decline because of non-viable population levels in the province. Plains spadefoot toads may be expanding their range in North America but local populations may be threatened by development that endangers breeding ponds, such as wetland draining and conversion of land to agriculture. The use of pesticides, herbicides, and the presence of other pollutants in water may also be a threat to these frogs.

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

IUCN Red List of Threatened Species: least concern

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Life Cycle

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Plains spadefoot toad eggs usually hatch within two days of being laid. At 30 degrees Celsius eggs hatch in 20 hours. Tadpole development (time to metamorphosis) usually lasts 13 to 20 days, depending on ambient temperatures. In northern parts of the range, time to metamorphosis may be up to 60 days, with average times in Alberta being 21 to 34 days. Tadpoles reach up to 7 cm in length and have a dark olive/yellow color with irridescent highlights. Plains spadefoot toad larvae develop primarily in small, temporary ponds and larvae are tolerant of widely fluctuating and high water temperatures. They metamorphose rapidly, before breeding ponds evaporate. As members of the family Pelobatidae, plains spadefoot toads have one of the fastest development rates among amphibians.

Development - Life Cycle: metamorphosis

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Benefits

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There is no known negative economic importance for humans.

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Benefits

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Plains spadefoot toads are important members of the healthy ecosystems in which they live.

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Associations

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Plains spadefoot toads affect populations of their invertebrate prey. They also share breeding ponds with other spadefoot toad species (Spea) and with Great Plains toads (Anaxyrus cognatus). Plains spadefoot toad tadpoles will eat Anaxyrus cognatus tadpoles where they share breeding ponds. They also share breeding ponds with Woodhouse's toads, Anaxyrus woodhousii woodhousii.

Plains spadefoot toads will outcompete Mexican spadefoot toads (Spea multiplicata) for fairy shrimp (Anostraca) where they co-occur.

Tadpoles are sometimes infected with Saprolegnia fungus. Adults have been found with intradermal mites (Acari) and may carry a monogean parasite, Pseudodiplorchis americanus.

Commensal/Parasitic Species:

  • intradermal mites (Acari)
  • monogean parasite, Pseudodiplorchis americanus
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Trophic Strategy

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Plains spadefoot toad tadpoles can develop into carnivorous "trophic morphs" or omnivorous "trophic morphs." Carnivorous tadpoles develop faster than omnivorous tadpoles and eat other spadefoot toad tadpoles and invertebrates. Cannibalism in breeding ponds is common. Omnivorous tadpoles eat organic matter, especially algae.

Adult plains spadefoot toads eat small invertebrates, such as hymenopterans, flies, moths, beetles, spiders, and stink bugs.

Animal Foods: amphibians; insects; terrestrial non-insect arthropods; terrestrial worms

Plant Foods: algae

Other Foods: detritus

Primary Diet: carnivore (Insectivore , Eats non-insect arthropods)

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Distribution

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Plains spadefoot toads, Spea bombifrons, are native to the Nearctic region. Their North American range stretches from southern Alberta and Saskatchewan, Canada south to the panhandle and lower tip of Texas, and into northern Mexico. They range as far west as southeastern Arizona and east to Nebraska, western Missouri, and western Oklahoma. Their range seems to be expanding along the Missouri River floodplain and in southern Alberta and Saskatchewan. There are disjunct populations in southern Colorado, northeastern Mexico, southernmost Texas, and along the Arkansas River in Arkansas.

Biogeographic Regions: nearctic (Native )

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Habitat

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Plains spadefoot toads are found mainly in the arid grasslands of western North America. They are restricted to areas with loose soils for burrowing. They can also be found in savannas, loess hills, sandhills, and semi-desert and desert scrub. They are found in shallower summer burrows and deeper winter burrows throughout the year. Larvae require small, ephemeral ponds for development, such as cattle ponds, vernal pools, playa lakes, and flooded agricultural fields. Suitable ponds are difficult to find in habitats that plains spadefoot toads prefer. The soft, sandy soils they prefer for burrowing are also usually permeable to water. Because of this they also require proximity to areas where soils are less permeable and permit formation of temporary breeding pools. Juveniles burrow into soft mud along the ponds in which they developed or crawl into crevices in dried mud or under plant litter.

Range elevation: 700 to 7500-8000 m.

Habitat Regions: temperate ; terrestrial

Terrestrial Biomes: desert or dune ; savanna or grassland ; chaparral ; scrub forest

Aquatic Biomes: lakes and ponds; temporary pools

Other Habitat Features: agricultural

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Life Expectancy

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The maximum lifespan of plains spadefoot toads is estimated at 13 years.

Typical lifespan
Status: wild:
13 (high) years.

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Morphology

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Plains spadefoot toads measure 38.1 to 63.5 mm (2 to 2.5 inches) in length, and weigh approximately 30 grams. Females tend to be slightly larger. They are brown or gray, sometimes with hints of green, and dark splotches or warts. On their dorsal and lateral surfaces are 4 vague stripes, with the middle two stripes sometimes forming an hourglass-like shape. Some have red or orange spots as well. Plains spadefoot toads are called "spadefoot" because of a welll-developed, sharp, spade-shaped and black tubercle on each of their rear feet. This is a bony extension of the metatarsal, covered with keratin that is used to burrow with the rear feet. There is a raised bone (or "boss") between their eyes, and their pupils are vertical, like those of cats. Adult, breeding males have a keratinous "nuptial pad" on their thumbs.

Plains spadefoot toads are not true toads (Bufonidae). They are members of a small, frog family, Pelobatidae.

Average mass: 30 g.

Range length: 38.1 to 63.5 mm.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

Sexual Dimorphism: female larger; sexes shaped differently

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Associations

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The cryptic coloration and burrowing habits of Spea bombifrons may protect many individuals from predation. They also have noxious skin secretions that may deter predators. Tadpoles gather in large feeding aggregations when they detect a predator, which may protect some individuals.

Hydrophilid beetle larvae (Hyrus triangularis), crustaceans (Apus), and other spadefoot toad tadpoles prey on tadpoles. Adults may be preyed on by barn owls (Tyto alba), Swainson's hawks (Buteo swainsoni), prairie rattlesnakes (Crotalus viridis), and burrowing rodents.

Known Predators:

  • Hydrophilid beetle larvae (Hyrus triangularis)
  • crustaceans (Apus)
  • barn owls (Tyto alba)
  • prairie rattlesnakes (Crotalus viridis)
  • burrowing rodents (Rodentia)

Anti-predator Adaptations: cryptic

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Reproduction

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After heavy rains, males travel to breeding ponds and begin to call. Calls attract both males and females, with louder choruses attracting the most individuals. Calls are loud and harsh and can be heard up to 3 km away. In some areas of the southwest Spea bombifrons uses the same breeding ponds as other Spea species and hybridization has been documented in the laboratory. Mating calls act as reproductive isolating mechanisms in these circumstances. Two mating call types have been identified in plains spadefoot toads. Spea bombifrons has been observed calling at mating ponds at temperatures as low as 10.5°C.

Mating System: polygynandrous (promiscuous)

Plains spadefoot toads mate during or after heavy rains (from 2.5 to 10.4 cm). Times of rainfall vary with latitude, but in the center of the range of S. bombifrons, this is from May to August. Plains spadefoot toads live primarily on land, traveling to breeding ponds only to mate. They lay their eggs in temporary ponds created by the rain. These ponds are generally up to 1 meter in depth. They have been observed breeding in natural ponds, oxbow areas of rivers, and sloughs as well as irrigation and roadside ditches, flooded areas of playgrounds and constructions sites, and in flooded agricultural fields. Females lay up to 2,000 eggs, in masses of 10 to 250. Eggs fall to the pond bottom or are attached to vegetation or other submerged objects. Sexual maturity is reached in the second year after hatching.

Breeding interval: Plains spadefoot toads may breed multiple times during a season, if conditions are good, or they may not breed in a year if conditions are poor.

Breeding season: Plains spadefoot toads will breed after periods of sufficient rain between the months of May and August.

Range number of offspring: 2000 (high) .

Range time to hatching: 2 to 3 days.

Average age at sexual or reproductive maturity (female): 2 years.

Average age at sexual or reproductive maturity (male): 2 years.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (External ); oviparous

After the eggs are deposited in a temporary pond, there is no further parental care.

Parental Investment: no parental involvement; pre-fertilization (Provisioning, Protecting: Female)

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Dewey, T. 2006. "Spea bombifrons" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Spea_bombifrons.html
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Plains spadefoot toad

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The plains spadefoot toad (Spea bombifrons) is a species of American spadefoot toad which ranges from southwestern Canada, throughout the Great Plains of the western United States, and into northern Mexico. Like other species of spadefoot toads, they get their name from a spade-like projections on their hind legs which allow them to dig into sandy soils. Their name, in part, comes from their keratinized metatarsals, which are wide instead of "sickle shaped". The species name translates as buzzing leaf shaped.[1] This refers to the species distinguishing features; its buzzing mating call, and its leaf-shaped digging metatarsals. First described by Cope in 1863.[2]

Description

The plains spadefoot toad generally grows from 1.5 to 2.5 inches (38 to 64 mm) in length, has a round body, with relatively short legs. These toads are usually a tannish to dark brownish color with visible orange spots. They are one of the easiest toads to recognize in their region because of their appearance looking more like a frog. Sometimes, they have light striping on their backs.

Evolutionary/Phylogenic relationships

The origins of Lissamphibia are not finalized. This has a lot to do with the fact that early stem amphibians were a lot more like amniotes in terms of biology. Much of amphibian biology appears to be derived evolution. The earliest known fossil of a burrowing frog is likely Prospea holoserisca.[3]

The most basal extant frog species are in the Archeabatrachia suborder. The most primitive frog is arguably Leiopelma.

Salienta fossils are the earliest examples of anurans that show a split from Order Caudata. Examples include Triadobatrachus and Czatkobatrachus.

Because amphibians might actually be highly derived, this could explain why their fossil record is poor. Multilocus sequence typing has proposed a Late Carboniferous/Early Permian origin around 270 mya.[4]

Geographical distribution and conservation status

This species is found throughout the Midwest from Alberta to Mexico wherever there is suitable soil for a fossorial lifestyle. The species is listed by IUCN 2015 as "least concern" and appears to be expanding its range, at least northwards into Alberta, Canada.

Ecology, Behaviour and Physiology

Spea bombifrons are famous for thriving in xeric environments, but a related species, Scaphiopus holbrookii has similar adaptation but does not live in similar extreme environments. The adults of this species is primarily fossorial for most of the year, but terrestrial during warm, wet periods. It only enters the water for breeding when nocturnal temperatures are at their yearly maximums and within 2–3 days of rain.[5] The tadpoles hatch from eggs after 2 days and metamorphose within 2 weeks. Froglets hide in cracks and shade and live off stored tissue in their tails until they can start feeding as adults.

Frogs can only live where the ground is suitable for burrowing, and reproduce within 1 km of where they aestivate.[5] Like all frogs, they are immobilized by low temperatures. This species prefers to burrow near large objects such as logs or rocks. They like to live near a water source, but this can be a subterranean patch of wet sand.

They have many predators, especially the hognose snake (Heterodon nasicus). Garter snakes predate most tadpoles, but often are not found in the desert, preferring riparian habitats. Many birds are opportunistic predators including burrowing owls and most wading birds. The tadpoles are also predated on by cannibal morphs, dragonfly larvae, giant scavenger beetles, and mosquito fish. Occasionally they will be eaten by Swainson's hawk and burrowing rodents.[6]

There have been a few parasites reported in at least 1 study: Polystoma nearcticum, Aplectana incerta, Aplectana itzocanensis, and Physaloptera spp.[7]

Behavior

Plains spadefoot toads are nocturnal and secretive. They spend most of the dryer seasons buried in the soil in estivation, typically only emerging during spring and fall rains. Breeding takes place in temporary pools of water left by rainfall, which requires the tadpoles to metamorphose quickly, before the water dries up. Eggs, laid in clutches numbering from 10 to 250, often hatch within 48 hours of being laid, and the larvae can change into tadpoles in as little as two weeks. The tadpoles exhibit phenotypic plasticity, with some changing from an omnivorous morphology into a cannibalistic carnivorous morph with oversized jaw muscles and pronged beaks. In some cases, female spadefoot toads will choose to mate with Spea multiplicata rather than with males of their own species, if the resulting hybrid tadpole would have higher chances of survival.[8] Character displacement has also been examined in ponds where Spea bombifrons and Spea multiplicata occur together. Reproductive and ecological competition between the two species likely causes selection for smaller and less reproductively successful individuals of Spea multiplicata. [9]

The adults travel by short hops and are generally poor swimmers. They swim in short bursts and only during periods of reproduction. this species is presumed to be non territorial and solitary except during breeding season. Satellite males have been shown to attempt to intercept females arriving at a breeding pond and are successful in about 20% of cases. Dominant, or first arriving males signal vocally from the deepest part of the ephemeral pool. Amplexus is a necessary stimulus to release eggs. Once the eggs are fertilized, there is little apparent parental care. The adults are strictly live insectivores. The tadpoles are detritivores, either scavengers or herbivores depending on morph

Tadpole "nests" can bee seen in most xeric amphibians, and are well described in the fossil record, such as at the St. George Dinosaur Discovery site. The shallow depressions are a form of "vortex feeding" used to stir up debris for feeding. It is also theorized that the depressions formed could allow a lengthened hydroperiod to increase growth size.

Sensory modalities

Both tadpoles and adults have many senses. Studies support a theory that olfactory sense is important to tadpoles of this species.[10] Adult breeding frogs detect breeding ponds by using auditory cues from other frog calls to gauge distance, size of pool, likelihood of predators and numbers as well as breeding condition of other frogs. Sources say frogs use low frequency sound of rain as a cue to emerge from aestivation.[11] While olfactory cues are considered a secondary emergence stimulus, there is evidence in other anurans that the smell of emergent plant growth can also guide frogs to breeding sites, specifically pond weed species. Persistent emergent behaviour has been observed personally when a piece of moss was placed in an enclosure of two captive Spea bombifrons.

Anuran tadpoles almost always have evidence of neuromasts arranged in lateral lines, although these only exist in adults of fully aquatic species, of which there are surprisingly few. There is poor research on how tadpoles use this sensory input during development.

Frog hearing is unique in that the lungs act as amplifiers for the hearing.[12] Their columella-operculum complex has been theorized as a method they can use to detect earthquakes.

Frogs have a unique form of green rods in their retinas which is theorized to help them see at very low light levels.[13]

Physiology

Frogs in general, but fossorial frogs specifically are able to absorb water through a "seat patch" instead of drinking. The skin is selectively permeable via aquaporins, allowing them to absorb water from damp ground, standing water, and mossy substrates.

According to David Pfenning's lab at the University of North Carolina, Desert spadefoots appear able to not only adapt their bodies to a carnivorous diet (Shorter gut, protein-digesting genes are activated) but also are more likely to have progeny that are adapted to meat. This is a major study that shows that Lamarckian characteristics are not as disproven as once thought.

Both Spea species found in North America have been used for many years in the North Carolina lab of Karin Pfennig as model organisms to study hybridization and its effects on competition and evolution.[14] The results appear to be mixed, but there is evidence of resource competition being linked to species divergence.

References

  1. ^ "Frogs and Toads - River Science". www.kansasriverscience.org. Retrieved 2019-11-12.
  2. ^ "Cope, 1863, Proc. Acad. Nat. Sci. Philadelphia, 15 | Amphibian Species of the World". research.amnh.org. Retrieved 2019-11-27.
  3. ^ Chen, C; Bever, S; Yi, Y; Norell., A (2016). "Chen, J., G.S. Bever, H. Yi, and M. A. Norell, 2016. A burrowing frog from the late Paleocene of Mongolia uncovers a deep history of spadefoot toads (Pelobatoidea) in East Asia. Scientific Reports. 6, 19209. [X23961] (matrix)". doi:10.7934/x23961. {{cite journal}}: Cite journal requires |journal= (help)
  4. ^ San Mauro, Diego; Vences, Miguel; Alcobendas, Marina; Zardoya, Rafael; Meyer, Axel (2005-05-01). "Initial Diversification of Living Amphibians Predated the Breakup of Pangaea". The American Naturalist. 165 (5): 590–599. doi:10.1086/429523. ISSN 0003-0147. PMID 15795855. S2CID 17021360.
  5. ^ a b Bragg, Arthur (1965). Gnomes of the Night: The spadefoot toads. University of Pennsylvania Press. p. 50. ISBN 9781512800678.
  6. ^ Lannoo, Michael (2005). Amphibian Declines: The Conservation Status of United States Species. University of California Press. ISBN 9780520235922.
  7. ^ Goldberg, Stephen (2002). "Helminths of the plains spadefoot, Spea bombifrons, the western spadefoot, Spea harmondi, and the Great Basin spadefoot, Spea intermontana (Pelobatidae)". Western North American Naturalist. 62 (4): 13.
  8. ^ Pfennig, Karin S. (2007-11-09). "Facultative Mate Choice Drives Adaptive Hybridization". Science. 318 (5852): 965–967. Bibcode:2007Sci...318..965P. doi:10.1126/science.1146035. PMID 17991861. S2CID 31080177.
  9. ^ Pfennig, Karin S; David W Pfennig (October 2005). "Character displacement as the "best of a bad situation": fitness trade-offs resulting from selection to minimize resource and mate competition". Evolution. 59 (10): 2200–2208. doi:10.1111/j.0014-3820.2005.tb00928.x. ISSN 0014-3820. PMID 16405163.
  10. ^ Mitchell, M (2018). "Olfactory cues of habitats facilitate learning about landscapes of fear". Behavioral Ecology. 29 (3): 693–700. doi:10.1093/beheco/ary024.
  11. ^ Dimmitt, M (1980). "Environmental correlates of emergence in spadefoot toads (Scaphiopus)". Journal of Herpetology. 14 (1): 21–29. doi:10.2307/1563871. JSTOR 1563871.
  12. ^ Schoffelen, R (2008). "Mechanics of the exceptional anuran ear". Journal of Comparative Physiology A. 194 (5): 417–428. doi:10.1007/s00359-008-0327-1. PMC 2323032. PMID 18386018.
  13. ^ Yovanovich, CAM (2017). "The dual rod system of amphibians supports colour discrimination at the absolute visual threshold". Philosophical Transactions of the Royal Society B. 372 (1717): 20160066. doi:10.1098/rstb.2016.0066. PMC 5312016. PMID 28193811.
  14. ^ Garcia, N (April 2015). "Leptin Manipulation Reduces Appetite and Causes a Switch in Mating Preference in the Plains Spadefoot Toad (Spea bombifrons)". PLOS ONE. Ecollection 2015 (4): e0125981. Bibcode:2015PLoSO..1025981G. doi:10.1371/journal.pone.0125981. PMC 4412710. PMID 25919309. S2CID 17163233.
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Plains spadefoot toad: Brief Summary

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The plains spadefoot toad (Spea bombifrons) is a species of American spadefoot toad which ranges from southwestern Canada, throughout the Great Plains of the western United States, and into northern Mexico. Like other species of spadefoot toads, they get their name from a spade-like projections on their hind legs which allow them to dig into sandy soils. Their name, in part, comes from their keratinized metatarsals, which are wide instead of "sickle shaped". The species name translates as buzzing leaf shaped. This refers to the species distinguishing features; its buzzing mating call, and its leaf-shaped digging metatarsals. First described by Cope in 1863.

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