Great Basin spadefoot (Spea intermontana) COSEWIC assessment and status report: chapter 3

Species Information

Name and classification

The Great Basin Spadefoot (Anura: Scaphiopodidae: Spea intermontana, Cope, 1883) is one of four species of western North American spadefoots of the genus Spea; the other three species are S. hammondii, S. bombifrons, and S. multiplicata (Crother et al. 2000). The genus Spea was originally named by Cope (1875). For many years, Spea was widely considered only a subgenus of Scaphiopus (V.M. Tanner 1939). W.W. Tanner (1989a,b), Stebbins and Cohen (1995), Crother (2000), and others now consider Spea to be a valid genus. Species of Spea are smaller in body size compared to Scaphiopus, have wedge-shaped (rather than sickle-shaped) “spades”, and lack dermal plates of the skull. Garcia-Paris et al. (2003) examined phylogenetic relationships of North American and Eurasian spadefoots using mtDNA markers and concluded that the North American and Eurasian members of the nominal family Pelobatidae were not monophyletic. They revived the family Scaphiopodidae for the North American genera Spea and Scaphiopus and retained the remaining genera found in Europe and Asia in the family Pelobatidae.

Cope (1883) described Spea intermontana as a subspecies of the Western Spadefoot, S.hammondii. Tanner (1939) was the first to consider S. intermontana as a valid species separate from S. hammondii, a treatment that is now widely accepted (Collins 1990, Crother 2000). Reflecting changes in nomenclature, Spea intermontana is referred to as Scaphiopus intermontanus in much of the literature prior to 1990.

Morphological description

Spea intermontana is a small to medium-sized anuran amphibian with adult body size (snout-vent length) about 40 – 65 mm (Tanner 1989b, Hallock 2005, Matsuda et al. 2006). Adults are grey-green with numerous dark brown or reddish tubercles and spots (Fig. 1). Limbs are relatively short and the snout is blunt and angled upwards slightly. Like all members of the family Pelobatidae, adults have a characteristic black, keratinous ridge (spade) on the sole of each hind foot. Great Basin Spadefoots have vertical, lens-shaped pupils, giving them a “cat’s-eye” appearance, and a glandular bump, termed boss, between the eyes. Males are somewhat smaller than females, have dark throats, and develop black pads on their inner three fingers during the breeding season (Hallock 2005, Matsuda et al. 2006). The advertisement call of males is a low, grating “gwaah”, repeated over and over and audible to the human ear from more than 200 m away. The loud calls and continuous chorus create a strong “assembly call”, typical of explosive breeders, i.e., amphibians that aggregate and breed in a very short period of time in response to environmental cues (Stebbins and Cohen 1995).

Figure 1. Spea intermontana adult, Penticton, BC. (Steve Cannings photo).

Figure 1.Speaintermontana adult, Penticton, BC. (Steve Cannings photo).

The egg masses consist of small (15 – 20 mm in diameter), grape-like clusters of about 20 – 40 eggs. Individual eggs are small (up to 5 mm in diameter, including the jelly layer) and loosely attached to each other. In dorsal view, tadpoles have a triangular-shaped head that appears distinct from the trunk. The closely set eyes are raised, and nostrils are prominent. The tail fin is high and terminates where the tail joins the trunk. The colour is dark with metallic flecking. Total length of tadpoles just before metamorphosis is about 30 – 70 mm (Hallock 2005, Matsuda et al. 2006).

Genetic description

Allozyme analyses by Wiens and Titus (1991) indicate that populations of S. intermontana from Oregon and Colorado are more distinct from each other than the Colorado population is from S. bombifrons. Crother (2000) noted that geographic variation of S. intermontana remains poorly documented across its range and that the nominal species may be a composite of two or more species. No genetic studies have been conducted of populations of S. intermontana in British Columbia, and the distinctness of different geographic subpopulations remains unknown.

Page details

Date modified: