Chihuahuan Green Toad

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Anaxyrus debilis (Girard, 1854)

Adults males to 46 mm SUL and females to 50.3 mm SUL (Sullivan 1984); tadpoles transform at about reach 25.1 mm. The Western Chihuahuan Green Toad is an attractive anuran, most easily confused with the Sonoran Green Toad, but the two can be distinguished based on the dorsal pattern.  This species has many isolated dark spots, while the Sonoran Green Toad has the black pigment organized in a more continuous net-like pattern. The small size, coloration and flattened, wedge-shaped head make it readily recognizable. The distributions do not overlap.  Cranial crests are reduced, parotoid glands are elongate and large; the tympanum is small and indistinct; the venter is pale with dark spotting. Males tend to be green; females are more yellow.Other characteristics useful for identification: warts on parotoid glands with narrow bases and distinct black-tips;  cranial crests reduced to a discontinuous series of black-tipped warts; suborbital ridge extending no further forward than to just below preorbital ridge; warts on upper eyelid with definite black points; thenar tubercle (base of thumb) much larger than subarticular tubercles (ventral side of digits); dorsal coloration usually composed of irregular, black lines and dots scattered on a gray or brown (green in life) ground color, often spotted or reticulate in Mexican specimens, no lateral light stripes (Savage 1954).The tadpoles are light in color with black stippling and gold patches on the dorsum.  Zweifel (1970) described the newly hatched larva as pale yellow tan, with only a trace of dark pigment in the form of a few melanophores on the dorsum. Through stage 25 the tadpole remains essentially yellow and translucent, although the number of melanic cells increases and they appear over much of the body and on the tail musculature. Late in stage 25 the first xanthophores appear on the back and on the base of the tail. In later stages the melanophores form an even stippling over the body and tail musculature. Patches of golden cells are present on the tail musculature, and such cells are more prominent than melanophores on the dorsal surface of the body. The deep abdominal region is black laterally with golden flecks, but the gular and mid-abdominal regions are without melanic pigment. The first melanophores appear in the dorsal tail fin in stage 28 and gradually form a general peppering, occasionally with dendritic orientation. Only in the largest tadpoles examined (stage 36) was there melanic pigment in the ventral fin. Overall, the larvae are much paler than is usual in Bufo. In contrast to the dense black aspect common to many Bufo tadpoles, these are relatively transparent even when well grown.Voice. The call is a wheezing buzz lasting two to twenty seconds, repeated at intervals of about five seconds.Distribution and Habitat. The distribution is discontinuous from southeastern Colorado and Kansas to Tamaulipas, San Luis Potosí, and Zacatecas, Mexico, and from southeastern Arizona to eastern Texas.  The Western Chihuahuan Green Toad is associated with the Chihuahuan Desert in extreme southeastern Arizona.  To the west is its Sonoran Desert counterpart, the Sonoran Green Toad, is similar in appearance, but their ranges are exclusive of each other.The Chihuahuan Green Toad inhabits shortgrass prairies and semi-desert grasslands, as well as mesquite and creosote flats below 1,500 m.  Its flattened head and body suggest it uses crevices as refugia.  Its limbs are poorly developed, and it may not dig its own burrow.  Instead, it may need to use burrows made by other animals.  It occurs in streams and washes. It is also sometimes a commensal with Black-tailed Prairie Dog colonies and the nests of Cockerel’s Desert Ant.Western Chihuahuan Green Toad is usually below 1,524 m ASL.  The habitat in Arizona has been described as grasslands (Lowe 1964), and semidesert grasslands (Brennan and Holycross 2006); in Colorado and Kansas the habitat was described as plains grasslands, open grass plains an native prairie (Hammerson 1982a, Collins 1982, Taggart 1997a); in New Mexico it uses low desert grasslands; mesquite and creosotebush; playa bottom grasslands, open bajada creosote (Creusere and Whitford, 1976; Degenhardt et al., 1996); in Oklahoma mesquite-shortgrass prairies, especially along valleys of small creeks; short-grass plains, mesquite savannas, and gypsum-hill regions; ecotone between short-grass plains and mixed prairie in Oklahoma (Bragg, 1950a,c; Black and Sievert, 1989); in Texas it uses arid and semiarid plains and grasslands (Garrett and Barker, 1987); in Mexico it occurs in xerophilic brushland and grasslands (Flores-Villela 1993).  In Chihuahua, Santos-Berra et al. (2008) found it in grassland and scrubland habitats. Green Toads often take refuge under rocks or in existing rodent or other burrows and may occur in grasslands that have been converted to agricultural ecosystems where herbicide and/or pesticide levels do not exceed lethal limits. Boeing et al. (2014) found Chihuahuan Desert populations tended to be associated with creosote shrubs and negatively associated with succulent vegetation.Green Toads are below ground and inactive from September–May in southern New Mexico (Painter 2005).  In Arizona the activity period is likely to be similar. The period of seasonal inactivity is longer at higher elevations and shorter at southern latitudes. It occurs in Chihuahuan Desert Scrub, (Holycross and Brennan 2006)Reproduction.  Spring and monsoonal rains trigger the males to move from drier, terrestrial habitat to aquatic breeding sites, they are followed by females who are attracted by chorusing males.  Green Toads breed in temporary ponds including stock tanks, rain pools, roadside ditches, or shallow pools on streams flood plains with an intermittent flow (Painter 2005).In Arizona this species is dependent on the summer monsoon while in other parts of the range spring and summer rains initiate reproduction. Breeding occurs from late March to mid-June (Wright and Wright 1949) and into late July (Sullivan, 1984; Degenhardt et al., 1996).  Taylor (1929) reported chorusing on 8 August in extreme southwestern Kansas, and Bogert (1962) reported males calling during the first 2 weeks of August in southwestern New Mexico.  Taggart (1997a) observed breeding behavior from 12 June–2 September in Kansas.Goldberg (2019) examined a sample of thirty-one A. debilis insidior collected 1963 to 1993 from New Mexico consisting of 16 adult males (mean SUL = 40.2 mm, range = 35-45mm), and 15 adult females (mean SUL = 45.3, range = 40-53 mm). All 16 males (July n = 14, August n = 2) exhibited spermiogenesis. The smallest reproductively active male measured 35 mm SUL and was from July. Wright and Wright (1949) reported adult male A. debilis ranged from 26 to 41 mm SUL. Two stages were present in the ovarian cycle; Females in spawning condition contained yolk filled oocytes predominated. (2) Females in post-spawning condition had few mature eggs were present. The post-spawning females were from July each contained postovulatory follicles from a recent spawning. The smallest reproductively active females (spawning condition) both measured 40 mm SUL and were from July and August. Anaxyrus debilis is reproductively active for longer periods of time in areas not dependent on summer monsoons. The time of breeding in New Mexico is June through August, it is likely the same in Arizona.Breeding aggregations last only one to three days in southeastern Arizona (Sullivan, 1984). Calling males are spaced 0.5 to 3.0 m apart.  Reproduction occurs from late March to September in ephemeral pools, including stock tanks, rain pools, and roadside ditches.  Calling males are slightly smaller than mature females.Eggs are laid in short strings or as single eggs attached to submerged vegetation.  Clutches may contain 1,000 or more eggs.Diet. Preys upon a variety of insects: ants, butterflies, beetles, and grasshoppers.  Smith et al. (2011) looked at the diets of three species of bufonids from northern Mexico, including Anaxyrus debilis. The diet of A. debilis was numerically and volumetrically dominated by termites, followed by ants. They found some aspects of prey size in A. debilis were correlated with toad head width but were not related to head length or body size.Defenses. Cei et al. (1968) report the presence of presumably toxic indolealklamines from the skin and paratoid glands of this toad.Predators. Known predators include American Bullfrogs (Stuart, 1995), Checkered Garter Snakes (Stuart and Painter, 1996), Plains Garter Snakes and Tiger Salamanders (Taggart, 1997a).  Eggs and tadpoles may be attacked by a host of invertebrate predators including Odonata (dragonfly larvae), Hemiptera (Notonectidae—backswimmers; Belostomatidae–giant water bugs), Coleoptera (Dytiscidae— predaceous diving beetles; Hydrophilidae— water scavenger beetles).  Tadpoles and adults may also be preyed upon by Black-necked Garter Snakes, ravens, raccoons, and skunks (Painter 2005). Kasper (2014) found a dead individual under the nest of a pair of Great Horned Owls.Taxonomy. Originally described by Girard (1854:87) as Bufo debilis based on nine syntypes USNM 2621 (eight specimens) and 2620 (lost) with a type locality that was given as lower part of the valley of the Rio Bravo (Rio Grande del Norte), and in the province of Tamaulipas, Mexico. Kellogg (1932:51-52), noted that the locality information for USNM 2620 states “between the Salado River (which empties into the Rio Grande near the town of Guerrero in Tamaulipas) and Camargo in Tamaulipas”, Mexico and that 2621 (originally a lot of 8 newly metamorphosed young) are from Matamoros in the State of Tamaulipas, Mexico. Girard (1854:87) also described Bufo insidior based on the syntypes: USNM 2622 (2 specimens) with the type locality reported as Chihuahua. Smith (1950:75) used the combinations Bufo debilis insidior and Bufo debilis debilis. Frost et al. (2006) moved B. debilis to the genus Anaxyrus. Later the combinations of Anaxyrus debilis debilis and Anaxyrus debilis insidior were used by Frost et al. in Crother (2008:3). Bufo (Anaxyrus) debilis was used by Fouquette and Dubois, 2014: 300.Peralta-García et al. (2016) tested the phylogenetic position of Anaxyrus kelloggi, a distinctive toad from coastal northwestern Mexico, using a fragment of mitochondrial ribosomal RNA gene regions and recovered phylogenetic topologies, which provide strong support for placement of A. kelloggi in the debilis group, as sister taxon to the clade formed by A. debilis and A. retiformis. Species relationships within the debilis group are also well supported and concordant with aspects of earlier, morphology-based hypotheses.[/vc_column_text][/vc_column][/vc_row]