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Anaxyrus cognatusGreat Plains Toad

By Amber Martin

Geographic Range

The Great Plains toad (Anaxyrus cognatus) can be found throughout central and southwestern North America. It extends as far north as North Dakota and northwest into Alberta, Canada, and extends as far south as central Mexico, and southwest as Arizona into southern California. The range of the Great Plains toad continues eastward as far as northwestern Iowa and northern Missouri. ("Anaxyrus cognatus", 2015; Lannoo, 2005)

Habitat

Great Plains toads are primarily found in grasslands. Their habitats include short grasses, deserts, open floodplains, and agricultural areas where irrigation ditches can be found. The toads burrow underground about 15-55 cm during hot and dry weather and burrow below the frostline during late summer and fall for hibernation. They stay in that burrow until they emerge after heavy rainfall or the start of breeding season. They also make use of temporary freshwater ponds (e.g., rain pools) and bottomland hardwood forests for breeding.

The highest elevation that the Great Plains toad has been found is 2,440 meters. (Dodd, 2013; "Anaxyrus cognatus", 2015; Lannoo, 2005)

  • Aquatic Biomes
  • lakes and ponds
  • temporary pools
  • Range elevation
    2440 (high) m
    8005.25 (high) ft

Physical Description

Great Plains toads have a snout-vent length from 47 mm to 115 mm. The females are about 49 to 115 mm in length, while the slightly smaller males range from 47 to 103 mm. The toads' overall color is olive with pale gray brown. They have large dark green blotches over the dorsal area, which are covered in granular glands. There is also a faint white stripe down the posterior portion of the body starting at mid-dorsal area. The bellies are primarily white and rarely have spots. To help with digging burrows, they have small and large spurs on the heels of their hind feet. At the toads' eyes, the cranial ridges come together at the snout and make a raised knob.

The toad's mass is approximately 40 grams on average with a basal metabolic rate of approximately 8.5 cm^3 oxygen per hour. Like other amphibians, the Great Plains toad is ectothermic.

The Great Plains toad tadpoles are up to 25.4 mm in length. The tadpoles are either black or dark brown in color, with metallic spots. The tail fins are clear with a rounded tip. ("Status of the Great Plains toad (Bufo [Anaxyrus] cognatus) in Alberta: Update 2009", 2009; Bennett and Ruben, 1979; Dodd, 2013; Lannoo, 2005; VanDeWalle, 2011)

  • Sexual Dimorphism
  • female larger
  • Average mass
    40 g
    1.41 oz
  • Range length
    47 to 115 mm
    1.85 to 4.53 in
  • Average basal metabolic rate
    8.5 cm3.O2/g/hr

Development

The Great Plains toad develops through a metamorphosis from tadpole to juvenile toadlet, then grows into an adult. Metamorphosis starts from 17 to 45 days after hatching when the snout-vent length is at 10 mm.

After hatching, the tadpole will begin to swim. When the tadpole reaches 8 mm, the black-speckled color pattern will appear. At 20-25 mm in length, the tadpole's mouth is fully formed and the formation of hind legs will begin. The total larval period, which is the time from egg to toadlet, was on average found to be between eighteen to forty-nine days.

Even though metamorphosis has an 89% success rate (Dodd 2013), some tadpoles will not survive because of predation and competition for limited food resources in a drying wetland. With a high density of over 10,000 tadpoles in a small breeding pond, the survival rate is low, while lower densities have a higher success rate in small ponds. (Bragg, 1936; Dodd, 2013; Krupa, 1994; Lannoo, 2005)

Reproduction

The Great Plains toad uses a polygynandrous mating system by having multiple females mate with multiple males. It also uses explosive breeding, with up to 500 toads gathering and competing for mates. In these breeding events, there are more males than females in the population. The male will vocalize in a chorus, and the female chooses the male with the loudest and longest call. If the breeding pond has a density over 500 male toads, the male toad will go searching for the female.

The male Great Plains toad cannot determine male from female, so it operates on a trial-and-error mating system with the male making release calls if mounted by another male.

With the use of external fertilization, the male toad will position himself onto the female's posterior by clasping in the basket posture. The position involves the male mounting the female with an arched back that places his legs in between the female's hind legs. This ensures that when the female releases the eggs, the male is able to catch them with his legs and hold them until they are fertilized with his sperm. (Dodd, 2013; Krupa, 1988; Krupa, 1994)

The Great Plains toad has an aquatic breeding environment during early to midsummer, but can change due latitude and environment. For example, in Alberta, Canada, the breeding season is in mid-June and lasts for about ten days while slightly lower latitudes like Colorado have the breeding season from May to June. Breeding will occur outside of these breeding season limits when there is rainfall that is greater than 25 mm. The toad reproduces multiple times throughout its lifetime, using external fertilization.

Multiple females will use the same oviposition site through the breeding season. The eggs come in clutches of 1,300 to 45,000 eggs per clutch with an average of about 11,074 eggs. The number of eggs laid are positively correlated to the body size of the female. Females and males both reach sexual maturity at two to five years old. The males reach this maturity at 47-103 mm SVL and the females reach at 49-115 mm SVL.

The eggs of the Great Plains toad will hatch in two to seven days after being laid. Independence immediate upon hatching. Birth mass has not been reported. (Dodd, 2013; Krupa, 1994; Lannoo, 2005; Sullivan, 1983)

  • Breeding interval
    Great Plains toads breed for two to ten days after rainfall during the summer months
  • Breeding season
    early to mid-summer
  • Range number of offspring
    1,300 to 45,000
  • Average number of offspring
    11,074
  • Range time to hatching
    2 to 7 days
  • Average time to independence
    0 days
  • Range age at sexual or reproductive maturity (female)
    2 to 5 years
  • Range age at sexual or reproductive maturity (male)
    2 to 5 years

There is no parental care for the Great Plains toad beyond the investment of eggs and sperm. Eggs are laid in oviposition sites and left during growth. (Dodd, 2013)

  • Parental Investment
  • no parental involvement

Lifespan/Longevity

The Great Plains toad has an average lifespan of 10 years in the wild, with a maximum of 20 years. In drier environments, such as the Sonoran Desert, the longevity is decreased to six years.

In captivity, the longest lifespan of the toad has been recorded at 10 years, eight months, and 10 days. (Lannoo, 2005)

  • Average lifespan
    Status: wild
    20 years
  • Average lifespan
    Status: captivity
    10.7 years
  • Typical lifespan
    Status: wild
    6 to 10 years
  • Average lifespan
    Status: captivity
    10.7 years
    AnAge

Behavior

The Great Plains toad is a solitary, fossorial species that remains mostly dormant in burrows during the day and can spend five to six days without moving. The toad will spend 63 to 77 percent of the year in this dormant state through aestivation and torpor. The majority of adult activity is at night during the dry season. However, the juvenile toad is also active during the day.

About a month after the larvae go through metamorphosis, the juvenile toad will migrate toward agricultural fields to burrow in the ground. It may leave the breeding pond sooner if the pond begins to dry up. The toad will move simultaneously with the other newly-developed toads to the burrow site due to a post-metamorphic chemical attraction. This pheromone chemical is released by the toad in order for the others to follow to the burrow site. This attraction is the only shown sign of social interaction other than reproduction.

The adult Great Plains toad is terricolous, utilizing a dense cover of mud or vegetation to avoid detection by predators. The use of cover is not related to regulating the toad's body temperature, as its body temperature is similar to the ambient temperature. The Great Plains toad can enter torpor by burrowing below the frostline (a maximum of 74 to 104 cm). While Dodd (2013) stated that heavy rainfall awakens the toad so that it can breed, he also found through Fischer et al. (1999) that the toad will awaken after a five week period of torpor.

During dry weather, the Great Plains toad will aestivate because it cannot survive long in temperatures higher than 43.5 degrees Celsius. It will burrow at least 15 cm in the ground and will stay dormant underground for at least 14 days. In order to stay moist, the toad can absorb water through the soil during this dormancy.

When not dormant, the Great Plains toad will seasonally migrate from overwintering sites to the breeding sites, then to a feeding site. The distance traveled from the hibernation areas to the breeding sites were found to be from 100 to 1,100 meters, while the food migration that occurs after breeding was 300 to 1,300 meters from the pond. (Dodd, 2013; Fischer, et al., 1999; Lannoo, 2005)

Home Range

The toad does not have a home range, but some will return to certain breeding ponds and overwintering areas multiple times. Its range has been described using linear distances, as most will travel more than 308 meters within its habitat. The average distance traveled was found to be 615 meters (maximum 815 meters per day).

The Great Plains toad does not actively defend a territory. There is a lot of overlap between the toad and other toad species without aggression towards a particular spot. (Dodd, 2013; Lannoo, 2005)

Communication and Perception

The Great Plains toad is a solitary species that does not usually interact with other members of its species until breeding season or when in the juvenile stage.

Males use loud and continuous advertisement calls that lasts about 20 to 50 seconds. The altogether sound (chorus) is made up of individual trills with the longest and loudest call attracting more mates. Females find mates through these advertisement calls rather that using sight or smell. They initiate reproduction by touching the male which gives them the cue to mount them.

Males will also use these loud calls to establish a small mating territory within the pond and will use aggressive calls to communicate to other males to move out of their mating area before they physically attack.

When under attack, the Great Plains toads will let out distress calls as a way to startle the predator into dropping them.

The Great Plains toads also use gonadotropin-releasing hormone (GnRH) and arginine vasotocin (AVT) for calling during breeding season, which affect their sexual behavior by making the intensity of an individuals' call increase in the chorus.

After reproduction occurs and metamorphosis of tadpoles is complete, juvenile toadlets will release pheromone chemicals when moving to the agricultural burrows so that other toadlets can detect the direction they need to move.

One way that the Great Plains toad perceives its environment is through colored vision called blue-mode wavelength. This is not used in actively hunting prey because it waits for prey to come to it, but is used in everyday stimuli detection. (Dodd, 2013; Elliott, 2004; Elliott, et al., 2009; Hailman, 1974; Lannoo, 2005; Rajchard, 2005)

Food Habits

The Great Plains toad does not travel to find food, but rather sits and waits for its prey. It mostly eats insects such as, mites, beetles, flies, moths larvae (cutworms) and ants. It will also eat arthropods, such as spiders. Feeding occurs mostly at night with a consumption rate of 12% of its body weight in that single feeding (Dodd 2013). The most common prey found in the Great Plains toad's stomach is the common black ground beetle (Pterostichus melanarius), which makes up about 66% of the toad's diet (Anderson et al. 1999). (Anderson, et al., 1999; Dodd, 2013; Lannoo, 2005; VanDeWalle, 2011)

  • Animal Foods
  • insects
  • terrestrial non-insect arthropods

Predation

As a defense mechanism, the Great Plains toad releases noxious secretions from its skin at the parotoids and dorsal warts. It also uses cryptic coloring (brown and green spots) that allows the toad to hide within its muddy environment. In order to avoid one of its main predators, snakes, the toad will use chemoreception to detect the predator's scent. If attacked, the toad will inflate itself in order to seem larger and frighten the predator. Known predators of the toad are the Plains garter snake (Thamnophis radix), the western hognose snake (Heterodon nasicus), the American crow (Corvus brachyrhynchos), the American badger (Taxidea taxus), the Virginia opossum (Didelphis virginiana) and the striped skunk (Mephitis mephitis).

The predators to the Great Plains toad tadpole are usually invertebreates (giant black water beetle Hydrophilus triangularis), the American crow, and the larvae of the Plains spadefoot toad (Spea bombifrons) and the western spadefoot toad (Spea hammondii). (Dodd, 2013; Lannoo, 2005)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

The Great Plains toad is usually a solitary species, but hybridization as been seen between it and the American toad (Anaxyrus americanus), Woodhouse's toad (Anaxyrus woodhousii), the red-spotted toad (Anaxyrus punctatus), the Texas toad (Anaxyrus speciosus), the Canadian toad (Anaxyrus hemiophrys) and the Colorado River toad (Incilius alvarius). These hybridizations do not occur often and are dependent upon close proximity of breeding pond location and habitat.

Parasitic invertebrates such as nematodes (Aplectana incerta, Aplectana itzocanensis, Oswaldocruzia pipiens, Physaloptera, and Rhabdia americanus) and cestodes (Cylindrotaenia americana, Ophiotaenia magna, and Distoichometra bufonis) have been found residing in the toad.

The Great Plains toad is an insect consumer in the food chain that performs soil aeration by burrowing in agricultural fields. (Dodd, 2013; Lannoo, 2005; "Status of the Great Plains toad (Bufo [Anaxyrus] cognatus) in Alberta: Update 2009", 2009)

Mutualist Species
Commensal/Parasitic Species
  • Nematodes (Aplectana incerta, Aplectana itzocanensis, Oswaldocruzia pipiens, Physaloptera, and Rhabdia americanus). cestodes (Cylindrotaenia americana, Ophiotaenia magna, and Distoichometra bufonis
  • Cestodes (Cylindrotaenia americana, Ophiotaenia magna, and Distoichometra bufonis

Economic Importance for Humans: Positive

To the benefit of humans, the Great Plains toad as been recorded as a major pest control for a specific species of sweet clover weevils (Sitona cylindercollis) in North Dakota with one-third of the toad's stomach containing their remains.

The toad is sold at about 13 dollars through online markets in the United States. (Hamilton, 1954; "Anaxyrus cognatus", 2015)

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

There is no physical harm towards humans, but the Great Plains toad has been seen as an agricultural nuisance and possible crop pest by burrowing within agricultural lands. Potato (Solanum tuberosum) crops are typically damaged more than others because of the softer, sandy soil in which it grows. ("Status of the Great Plains toad (Bufo [Anaxyrus] cognatus) in Alberta: Update 2009", 2009)

Conservation Status

The Great Plains toad currently has no federal or state protection and is listed as a species of "Least Concern" on the IUCN red list. There is not a lot of information on the conservation of the toad due to the difficulty of monitoring the burrowing and scattered species. The IUCN SSC Amphibian Specialist Group (2015) estimated that 11-20% of all population of this species already exist on lands that are protected, both in the U.S. and in Mexico.

One of the major threats to the Great Plains toad is a parasitic bacterium called, Mycobacterium marinum, which causes the fatal red-leg disease, Aeromonas. This disease produces infections in the intestines, respiratory system, liver, and skin of the toad.

While this species of toad is not largely threatened, the population has decreased due to human interaction. Mortality rates have increased because of a reduction in habitat area that is being used for farming, roadways, and urbanization. (Dodd, 2013; "Anaxyrus cognatus", 2015; Lannoo, 2005)

Contributors

Amber Martin (author), Radford University, Cari Mcgregor (editor), Radford University, Zeb Pike (editor), Radford University, Karen Powers (editor), Radford University, April Tingle (editor), Radford University, Jacob Vaught (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

choruses

to jointly display, usually with sounds, at the same time as two or more other individuals of the same or different species

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

diurnal
  1. active during the day, 2. lasting for one day.
ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

fossorial

Referring to a burrowing life-style or behavior, specialized for digging or burrowing.

freshwater

mainly lives in water that is not salty.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

migratory

makes seasonal movements between breeding and wintering grounds

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

saltatorial

specialized for leaping or bounding locomotion; jumps or hops.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

soil aeration

digs and breaks up soil so air and water can get in

solitary

lives alone

tactile

uses touch to communicate

terrestrial

Living on the ground.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

References

IUCN SSC Amphibian Specialist Group. 2015. "Anaxyrus cognatus" (On-line). The IUCN Red List of Threatened Species 2015 e.T54612A53949260. Accessed January 28, 2016 at http://dx.doi.org/10.2305/IUCN.UK.2015-4.RLTS.T54612A53949260.en.

Alberta Sustainable Resource Development and Alberta Conservation Association. Status of the Great Plains toad (Bufo [Anaxyrus] cognatus) in Alberta: Update 2009. 14. Edmonton, AB: ASRD, ACA. 2009.

Altig, R., R. McDiarmid. 2015. Handbook of Larval Amphibians of the United States and Canada. Ithaca, NY: Cornell University Press.

Anderson, A., D. Haukos, J. Anderson. 1999. Diet composition of three anurans from the Playa Wetlands of northwest Texas. Copeia, 1999/2: 515-520.

Bennett, A., J. Ruben. 1979. Endothermy and activity in vertebrates. Science, 206/4419: 649-654.

Bragg, A. 1936. Notes on the breeding habits, eggs, and embryos of Bufo cognatus with a description of the tadpole. Copeia, 1936/1: 14-20.

Dodd, C. 2013. Frogs of the United States and Canada, 2-vol. Set. Baltimore, MD: Johns Hopkins University Press.

Elliott, L. 2004. The Calls of Frogs and Toads, Volume 1. Mechanicsburg, PA: Stackpole Books.

Elliott, L., . Gerhardt, C. Davidson. 2009. The Frogs and Toads of North America: A Comprehensive Guide to Their Identification, Behavior, and Calls. Boston, MA: Houghton Mifflin Harcourt.

Farr, W., D. Lazcano, P. Lavin-Murcio. 2009. New distributional records for amphibians and reptiles from the state of Tamaulipas, Mexico II. Herpetological Review, 40/4: 459-467.

Fischer, T., D. Backlund, K. Higgins, D. Naugle. 1999. A Field Guide to South Dakota Amphibians. Brookings, SD: South Dakota Agricultural Experiment Station Bulletin 733.

Hailman, J. 1974. Phototactic responses to spectrally dominant stimuli and use of colour vision by adult anuran amphibians: A comparative survey. Animal Behaviour, 22/4: 757-795.

Hamilton, W. 1954. The economic status of the toad. Herpetologica, 10/1: 37-40.

Krupa, J. 1989. Alternative mating tactics in the Great Plains toad. Animal Behaviour, 37/6: 1035-1043.

Krupa, J. 1994. Breeding biology of the Great Plains toad in Oklahoma. Journal of Herpetology, 28/2: 217-224.

Krupa, J. 1988. Fertilization efficiency in the Great Plains toad (Bufo cognatus). Copeia, 1988/3: 800-802.

Lannoo, M. 2005. Amphibian Declines: The Conservation Status of United States Species. Berkeley, CA: University of California Press.

Rajchard, J. 2005. Sex pheromones in amphibians: A review. Veterinary Medicine, 50/9: 385-389.

Ruibal, R. 1962. The adaptive value of bladder water in the toad, Bufo cognatus. Physiological Zoology, 35/3: 218-223.

Sullivan, B. 1983. Sexual selection in the Great Plains toad (Bufo cognatus). Behaviour, 84/3: 258-264.

VanDeWalle, T. 2011. Frog and Toads in Your Pocket: A Guide to Amphibians of the Upper Midwest. Iowa City, IA: University of Iowa Press.

Wells, K. 2010. The Ecology and Behavior of Amphibians. Chicago, IL: University of Chicago Press.

Wells, K. 1977. The social behaviour of Anuran amphibians. Animal Behaviour, 25/3: 666-693.

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