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
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:
Anti-predator Adaptations: cryptic
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
The maximum lifespan of plains spadefoot toads is estimated at 13 years.
Typical lifespan
Status: wild: 13 (high) years.
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
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 )
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)
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:
Plains spadefoot toads are important members of the healthy ecosystems in which they live.
There is no known negative economic importance for humans.
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
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
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)
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 projection on their hind legs which allows 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.[2] This refers to the species' distinguishing features; its buzzing mating call, and its leaf-shaped digging metatarsals. It was first described by Cope in 1863.[3]
The plains spadefoot toad generally grows from 1.5 to 2.5 inches (3.8 to 6.4 cm) 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 anurans to recognize in their region because of their unique appearance. Sometimes, they have light striping on their backs.
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.[4]
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.[5]
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.
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.[6] 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.[6] 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.[7]
There have been a few parasites reported in at least 1 study: Polystoma nearcticum, Aplectana incerta, Aplectana itzocanensis, and Physaloptera spp.[8]
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.[9] 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. [10]
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.
Both tadpoles and adults have many senses. Studies support a theory that olfactory sense is important to tadpoles of this species.[11] 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.[12] 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.[13] 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.[14]
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.[15] The results appear to be mixed, but there is evidence of resource competition being linked to species divergence.
{{cite journal}}: Cite journal requires |journal= (help) 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 projection on their hind legs which allows 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. It was first described by Cope in 1863.
