[vc_row][vc_column][penci_container][penci_column width=”11″][penci_fancy_heading p_title=”Scaphiopodidae” _title_typo=”font_family:%3A” _subtitle_typo=”font_family:Bad%20Script%3A%22regular%22|font_style:400%20regular%3A400%3Anormal” _subtitle_fsize=”0px” _desc_typo=”font_family:Merriweather%3A%22300%2C300italic%2Cregular%2Citalic%2C700%2C700italic%2C900%2C900italic%22|font_style:300%20light%20italic%3A300%3Aitalic” title_color=”#6b6311″][/penci_fancy_heading][/penci_column][/penci_container][vc_column_text]

Spadefoots

The Spadefoots (family Scaphiopodidae) are toad-like anurans but are not toads and are best simply referred to as spadefoots instead of spadefoot toads.  Two genera contain eight Western Hemisphere species. They mostly occur in deserts and dry grasslands from southern Canada southward to southern Mexico, but two species occur in the moister environments of the southeastern United States.  Spadefoots may live underground for ten months a year.  The low frequency sound from thunder or rain pounding the ground stimulates them to emerge from their burrows during heavy rains (Dimmitt and Ruibal 1980).A small, black mass of keratin on their heel—the spade—is the basis for their common name. The spade is used for digging, removing soil from directly below the toad.  Like many anurans, spadefoots dig burrows backward using their hind legs and feet.  They excavate the soil from under themselves and sink into the hole, leaving no trace that they lie beneath (Bragg 1944).  The presence of the spade combined with a horizontal pupil will separate Arizona members of this family from other families of anurans.Chen et al. (2016) describe the fossil spadefoot Prospea holoserisca, as member of the crown-group of spadefoot toads. This remarkable fossil is the first report a crown spadefoot toad from the late Paleocene of Mongolia. The phylogenetic analysis using both morphology and molecular information recovered this Asian fossil inside the modern North American pelobatoid clade Scaphiopodidae. The presence of a spade and the phylogenetic position of the new fossil frog strongly support its burrowing behavior. The late Paleocene age and other information suggest a mild climate and cast doubt on the conventional assertion that burrowing evolved as an adaptation to aridity in spadefoot toads. Temporally and geographically, the new fossil provides the earliest record of Scaphiopodidae worldwide and the only member of the group in Asia. Quantitative biogeographic analysis suggests that Scaphiopodidae, despite originating in North America, dispersed into East Asia via Beringia in the Early Cenozoic. The absence of spadefoot diversity in East Asia today is a result of extinction.The two North American genera, Scaphiopus and Spea, separated 29–20 million years ago (MYA) between the Oligocene and the Miocene, based on the fossil record. The species within Spea diverged within the last six million years.  The relatively recent diversification of Spea compared to that of Scaphiopus may explain why it is more difficult to distinguish the species of Spea than those of Scaphiopus.Spadefoot tadpoles accelerate their development when their pond is drying.  Kulkarni et al. (2017) report spadefoot tadpoles (both the Old World Pelobates cultripes and the New World Spea multiplicata) respond to drying ponds with rapid metamorphosis, increasing their standard metabolic rate, and elevating the thyroid and corticosterone hormones.  Both these hormones are involved in growth and controlling growth.  In contrast, the New World Scaphiopus couchii has the shortest larval period, the highest thyroid hormone and corticosterone levels, and the highest standard metabolic rate.  In Couch’s Spadefoot the hormone levels and metabolic rate are least affected by pond drying among the three species.  The results suggest that the atypically rapid development of S. couchii evolved by genetic accommodation of endocrine pathways controlling metamorphosis, showing how phenotypic plasticity within species may evolve into trait variation among species.Spadefoots are found over most of the state and are considered species of least concern when it comes to conservation.  However, human activity subjects them to a variety of environmental stressors.  Habitat fragmentation and pesticides are of concern.  The use of irrigation technology has destroyed some of the areas where spadefoots once lived.  Additional threats come from pesticides.  Dinehart et al. (2010) found the pesticide Roundup Weathermax® to be moderately toxic to spadefoot tadpoles.To escape extreme environmental conditions, spadefoots occupies burrows of varying depth depending on the time of the year. Ruibal et al. (1969) found that for a species of spadefoot in Arizona that closely resembles the Great Basin Spadefoot, winter and pre-summer burrows are on average deeper than the summer and early fall burrows. Presumably, burrows will tend to be shallower when soil moisture is high. In early fall, Ruibal et al. (1969) found the average burrow depth to be 24 cm, the period when the toads were getting ready to over-winter. Later in the fall, as the soils dry out, the spadefoots dig to deeper levels where they over- winter at an average depth of 54 cm. The deepest burrow found was 91 cm. Bragg (1965) however, found a spadefoot 7.6 meters below the surface. Spadefoots apparently anticipate rains and start to surface before the rains begin. The mechanism for this may be changes in air pressure and humidity.Spadefoots will sometimes emerge prematurely from their underground retreat because of low frequency sounds from motors, a phenomenon that can be fatal to all the spadefoots that emerge when humidity and precipitation are almost non-existent.The two genera can be separated from each other based on the condition of the skin covering the skull.  Scaphiopus has the skin fused to the skull, while Spea does not. Scaphiopus has a sickle-shaped spade, while the spadefoots in the genus Spea have a wedge-shaped spade.Four of the known spadefoot species occur in Arizona: Couch’s Spadefoot, Scaphiopus couchii; the Chihuahuan Desert Spadefoot, Spea multiplicata stagnalis; the Plains Spadefoot, Spea bombifrons; and the Great Basin Spadefoot, Spea intermontana.  Arizona spadefoots usually lack a parotoid gland, a trait that distinguishes them from the true toads (Family Bufonidae).The first specimens of western spadefoots appear to have been collected by Jean-Louis Berlandier. A Swiss-born, French naturalist, physician, and anthropologist, Berlandier settled in Matamoros, Tamaulipas, Mexico in 1829.  He served as a military officer and cartographer in Mexico’s Army and made extensive collections of Mexican plants and animals. Berlandier died in 1851 and his collections were purchased by Lieutenant Darius N. Couch, a Union officer during the Civil War and naturalist. Couch purchased the collections with his own money and shipped them to the Smithsonian Institution where Spencer Fullerton Baird described Scaphiopus couchii based on a Berlandier specimen. Unfortunately, the location the specimen came from remains unknown. But it has been hypothesized to have come from the Matamoros area, or some other place in Tamaulipas.Tanner (1990:503) discussing the relationships between Scaphiopus and SpeaI consider the skull of Scaphiopus, with its dermal plates, to be primitive. This characteris, I believe, more than a slight difference when compared with the skull of Spea. Theloss of the dermal plates in Spea is considered a derived character. Obviously, there aresimilarities that relate Scaphiopus and Spea, similarities that place them both in the North American branch of the family Pelobatidae. Based on the distinct differences in the skulls and other morphological, life history, and ecological differences discussed by Bragg (1944), Blair (1955, 1956), Zweifel (1956), and Kluge (1966), I am persuaded to accept Spea as a genus rather than to continue dealing with a Scaphiopus-Spea complex (Tanner 1989).[/vc_column_text][/vc_column][/vc_row][vc_row][vc_column width=”1/2″][penci_container][penci_column width=”11″][vc_single_image image=”3080″ img_size=”medium”][/penci_column][/penci_container][/vc_column][vc_column width=”1/2″][vc_column_text]The two genera of spadefoots can be distinguished by the shape of the spades on the bottom of the feet. Scaphiopus has a sickle-shaped spade and Spea has a wedged-shape spade.[/vc_column_text][/vc_column][/vc_row]