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Spea intermontana, Great basin spadefoot

Page history last edited by PBworks 13 years, 2 months ago

        Great basin spadefoot


                       Spea intermontana


   Photo taken by G. Nafis, taken from:  www.californiaherps.com/frogs/pages/s.intermontana.sounds.html





Kingdom - Animalia

  Phylum - Chordata

    Subphylum - Vertebrata

      Class - Amphibia

        Order - Anura

           Suborder - Salientia

              Family - Pelobatidae

                 Genus - Spea

                     Species - intermontana


-  Over the past 120 years the Great Basin Spadefoot toad has been taxonomically reclassified many times: Scaphiopus intermontana, Spea hammondii intermontanus, Scaphiopus intermontanus, Scaphiopus hammondii intermontanus,and now Spea intermontana.

-  Similar species of spadefoot toads include: Spea hammondii (western spadefoot), Spea bombifrons (plains spadefoot), and Spea multiplicata (southern spadefoot)





Great Basin spadefoot toads are typically 1.5 to 2.5 inches in length (snout-vent length).  They are small to medium sized with a broad waste, plump body, and a short upturned nose (pug nose).  Their most distinct feature is the wedge-shaped spade on each hind foot (as pictured below) and a glandular boss (hump) between the eyes.  The spade is sharp-edged, horny, and glossy black in appearance.  Their eyes are gold with a vertical black pupil and appear to have a stout body with short legs in comparison to body size.  The external ear drum is apparent and skin is relatively smooth with many minute tubercles present.  They have brownish to reddish tips on each of the skin tubercles.  The parotid glands are not present.  Their coloring is olive to gray-green above,with light stripes along flanks.  The ventral surface is white to cream colored without markings, except in males where the throat is dusky colored and nuptial pads (dark raised flesh) are present on the inner most front toes.


Tadpoles have a slightly flattened body shape, distinct nostrils, and closely set dorsal eyes.  They are mainly dark in color with light dorsolateral stripes. The dorsal fin extends just past the end of the tail tip and the end of the tail tapers slightly. The ventral surface consists of three longitudinal sections and a golden iridescence. The tadpoles have distinct triangular heads.   



 Photos taken by G. Nafis, taken from: www.californiaherps.com/frogs/pages/s.intermontana.sounds.html





The range of spadefoot includes the southern most region of British Columbia, Canada, south through the Great Basin to northern Arizona and New Mexico.  Populations exist from the eastern edge of the Sierran-Cascade Mountain shelf to the Rockies.  In California, populations are present east of the Sierra Nevada and north of San Bernadino County.  Washington, the Great basin spadefoot occurs throughout most of the Columbia River Basin and select northeast ecoregions.  Idaho populations are located primarily in southern Idaho, throughout the desert/ sagebrush regions.  They occur in Nevada and Utah east of the Colorado River.  Populations exist in northwest Arizona, north to northwest Colorado and southwest Wyoming.




Figure 1- Distribution map for the Great Basin Spadefoot Toad provided by: http://www.natureserve.org





Spadefoot toads are primarily terrestrial but will spend time in the water during the breeding season to lay eggs.  Spea intermontana are considered xeric-adapted amphibians.  They require a landscape with a water source for larval and tadpole developement during the spring and summer months.  During the non-breeding months, Spea intermontana prefer arid to semi-arid forested areas, such as forested areas, shrub-steppe and sagebrush flats.  Adults require habitats with beetles, beetle larvae, grasshoppers, crickets, ants, a wide variety of insects, arachnids, and snails.  They prefer habitat below 6,000 feet in elevation but have been found at elevations up to 9,200 feet.  Tadpoles require very little to survive.  Tadpoles scavenge on algae, aquatic plant matter, dead fish and invertebrates, and will scavenge on eachother.





Spadefoot toads are primarily nocturnal.  Metamorphs and juveniles emerge and are active on the surface during the daylight, often but not always, immediatley following a rainfall.  Adults can occasionally be found in the daylight, but can be found after periods of rainfall or agricultural irrigation.   They excavate burrows in loose soil or use already made rodent burrows.  The spades on their hindfeet assist in burrow cultivation.  Spadefoot toads back into their burrow by moving their feet with spades in a circular motion.  They spend 7 to 8 months in their burrow during the winter and summer months to escape extreme weather. They avoid predators by toxins within their skin. 





Spadefoot toads breed between April and July.  Usually (but not always) breeding takes place after warm summer or spring rain.  Adult Spea intermontana aggregate along water sources during the breeding season for only 1-3 days until the breeding season is complete.  Spea intermontana breed in springs, irigation ditches/ ponds, slow moving water, temporary ponds, and permanent bodies of water.  The female lays 200-500, which are laid in small loose packets usually containing 10-30 eggs each (as seen below in the photo on the right).  These eggs look like a cluster of grapes but much smaller in size.  The eggs are usually laid attached to vegetation, lieing in the bottom of a pool, or unattached to sediment.  Adult spadefoots are condsidered to be "explosive breeders" because all breeding is done within 1-3 days.  The eggs hatch in 2-3 days, depending on water conditions, and tadpoles mature in 1-2 months.  The hatch and tadpole maturation takes longer with colder water.



Photo on the left is taken from: http://animaldiversity.ummz.umich.edu/site/accounts/classification/Spea.html#Spea

Photo on the right is taken by G. Nafis, taken from:  www.californiaherps.com/frogs/pages/s.intermontana.sounds.html



Scientific study


Morey, S. R. and Reznick, D. N.  2004.  The relationship between habitat permanence and larval development in California spadefoot toads: field and laboratory comparisons of development plasticity.  Oikos 104: 172-190.


Most amphibian populations persist in metapopulations, a network of sub-populations connected by migration.  American spadefoot toads are good examples of the metapopulations.  Adult spadefoot toads migrate to breeding grounds each year as a means of linking sub-populations together through breeding season migration.  This study provides a comparative analysis of three spadefoot toad species located in California: Spea intermontana (Great Basin spadefoot), Spea hammondii (western spadefoot), and Scaphiopus couchii (desert spadefoot)There is no species overlap between the three spadefoot toad species.  The study takes place in a multitude of spadefoot toad natural breeding habitats, as well as in "common garden" or a laboratory settings.  The researchers determine if, species from stable environments show more levels of responsiveness to a changing environment that are distinguishable from the pattern of those that regularly encounter variability, among three closely related species. North American spadefoot toads provide a good example of a species with a large variation in larval environments and development.  Some spadefoot toads breed in temporary environments, so breeding and development must be rapid to escape desiccation.  Other species prefer more permanent breeding habitat, which allows for a longer breeding and development period.  The study focuses on an in depth look at the larval ecology and development amongst the three spadefoot toad species. 


The field portion of the study evaluates: larval growth and development, pool duration, age, and size at metamorphosis and risk of catastrophic mortality due to drying, and the changing abiotic environment.  The laboratory portion of the study evaluates: reaction norm, comparisons of growth in nature and lab, plastic response of developmental rate, and the age and size at metamorphosis.  The known breeding site tendencies for each of the spadefoot toad species is as follows: S. couchii populations prefer to breed in summer monsoon puddles and therefore have a short breeding/ larval development phase.  S. hammondii populations prefer to breed in pools created by winter snow melt off and have an intermediate time period to complete breeding/ larval development.  S. intermontana prefer permanent water supplies fed by snowmelt and have the longest time period to complete breeding/ larval development. 


Field Observations/ Results

Larval growth and development- The growth patterns for all three spadefoot toad species is found to be somewhat universal.  S. intermontan and S. hammondii however, are larger than S. couchii.  S. intermontana breeds asynchronously, meaning the breeding season is somewhat sporadic throughout the spring/ summer months and does not always follow a rainfall.  S. hammondii is a synchronous breeder; breeding only occurs during March and is restricted to breeding immediately after a heavy rainfall.   S. couchii is a synchronous breeder, breeding only occurs during heavy rainfalls.  Larval development for S. intermontana took 48 days with a range of 36 to 60 days.  Larval development for S. hammondii took 58 days with a range of 30 to 79 days.  Larval development for S. couchii took 7.4 days with a range of 7 to 8 days.  S. couchii are on average the smallest spadefoot toads upon metamorphosis, which means there is a correlation between larval development period, location, and size.  S. couchii are the smallest spadefoots because they prefer to breed in habitats that are not permanent (desiccation is an issue much faster in less permanent breeding habitats), which limits the amount of time to metamorphosis.


Pool duration, age and size at metamorphosis and risk of catastrophic mortality due to drying-  As previously mentioned, S. intermontana choose breeding habitat that are permanent, such as quiet pools, while the other two species choose temporary habitats for breeding habitat.  The correlation between mortality and breeding habitat supports permanent breeding habitats and S. intermontana.  A permanent breeding habitat allows for more time to develop because the risk of drying in a permanent water body is minute in comparison to choosing a temporary water source for breeding.  The S. couchii population prefer the least stable of breeding habitats and as a result, S. couchii, have the highest mortality of the three species.


The changing abiotic environment- The temperature of a breeding habitat, depending on the classification for the specific breeding habitat, tends to fluctuate.  Temporary breeding habitats, preferred by S. couchii, tend to stay at the same temperature for the duration of the breeding bout.  Permanent breeding habitats, such as those chosen by S. intermontana, tend to fluctuate in temperature.  The daytime temperature for permanent breeding habitats increases steadily throughout the breeding/ larval development phase.  The water chemistry for permanent breeding habitat remains stable for the breeding/ larval development time period.  The water chemistry of the temporary habitats fluctuates as the water supply dries (increases in the amount of dissolved substances, such as ammonium nitrate).  Water temperature and chemistry both correlate to survivor ability of spadefoot larva.


Laboratory Observations/ Results

Reaction norm- All three species were subject to controlled food availability for an unspecified amount of time.  With minimum food availability, all three spadefoot species tend to take a longer period of time to reach the metamorphosis stage of the larval development.  In contrast, with maximum food availability all three species reached a certain uniform species specific size and then went through metamorphosis.  The findings suggest that there is a maximum body size at metamorphosis.


Comparisons of growth in the lab and nature- The approximate milligram amount of food consumed by each species of spadefoot was estimated in the wild and replicated for lab use to compare consumption and growth rates in the lab versus nature.  Minimum food availability results in high mortality, both in a lab setting and in a natural setting.  Maximum food availability supports low mortality both in a lab setting and in a natural setting.  Given the opportunity to eat more than an average amount of food, larva in a lab setting typically do not eat more than they would in a natural setting. 


Plastic responses of development/ Age and size at metamorphosis- S. couchii develop the fastest from the time of hatching to metamorphosis, usually taking about 9.02 days.  S. hammondii develop the second fastest, taking 17.73 days to develop from the time of hatching to metamorphosis.  S. intermontana develop the slowest, taking about 20.13 days to develop from the time of hatching to metamorphosis.  With maximum food availability, the size for each species dramatically increased at the time of metamorphosis.  With maximum food availability the given species takes a longer amount of time to develop, and upon the time of metamorphosis the given species is at maximum body sizes. 










Morey, S. R. and Reznick, D. N.  2004.  The relationship between habitat permanence and larval development in California spadefoot toads: field and laboratory comparisons of development plasticity.  Oikos 104: 172-190.

Created By: Casey Clark


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