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Twin-spotted Spiny Lizard (Sceloporus bimaculosus)

[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column][/vc_row][vc_row][vc_column width=”1/2″][vc_single_image image=”1293″ img_size=”large” alignment=”center” style=”vc_box_rounded”][vc_column_text]Adult Twin-spotted Spiny Lizard, Graham County, AZ. Photo by Larry Jones[/vc_column_text][/vc_column][vc_column width=”1/2″][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”1898″ img_size=”medium” alignment=”center” onclick=”img_link_large”][vc_column_text]Juvenile Twin-Spotted Spiny Lizard, Rio Salado Dunes, NM. Photo by Larry Jones[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”1899″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Twin-spotted Spiny Lizard. Photo by Jim Rorabaugh[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][/vc_row_inner][/vc_column][/vc_row][vc_row][vc_column width=”1/6″][/vc_column][vc_column width=”2/3″][vc_column_text]

Description

The Twin-spotted Spiny Lizard (Sceloporus bimaculosus) is a large (< 121 mm SVL) spiny lizard with a tail that is at least 130% SVL, the dorsal scales are heavily keeled, and there are 11-15 femoral pores per thigh.  Five to seven long, pointed scales extend backwards over the ear opening.  The species is named for a single paravertebral row of dark spots on either side of the mid-dorsal line.  A lateral row of often darker and larger spots is present on each side, and just above that often there is a broad somewhat indistinct light stripe.  A dark, wedge-shaped marking is found on each side of the neck. These markings broaden ventrally and may merge on the throat in males.  Males also have dark patches in the groin.  The limbs are often streaked with fine, dark lines in males, and the tail, particularly in females and juveniles, has dark bars.  The ventral surface in males is characterized by blue on the throat and chin, and large, elongated blue patches on the abdomen usually separated by a creamy white stripe.  The blue patches are edged in black and meet mid-ventrally in some specimens.  In females and juveniles, the blue throat and abdominal patches are absent or much reduced (Phelan and Brattstrom 1955, Stebbins 1985, Webb 2009).

The similar Clark’s Spiny Lizard (Sceloporus clarkii) has dark bars on the dorsal aspect of the front limbs and 3 (rarely 4) scales that extend backwards over the ear openings.  The Desert Spiny Lizard (S. magister) is very similar to the Twin-spotted Spiny Lizard, and for many years the latter was considered a subspecies of the former.  The only character that distinguishes the two is that instead of rows of dark paravertebral spots, adult male Desert Spiny Lizards have a dark or purple mid-dorsal stripe 4-5 scales wide.  Genetically, authors disagree as to whether S. magister and S. bimaculosus are distinct species.  Schulte et al. (2006) split the wide-ranging Desert Spiny Lizard into three species: 1) S. uniformis of the Great Basin, Central Valley of California, and the Mohave Desert, 2) S. magister of the Sonoran Desert and Colorado Plateau, and 3) S. bimaculosus of the Chihuahuan Desert.  They suggested S. bimaculosus extends into southeastern Arizona, but their only genetic samples were from the Río Grande Valley of New Mexico.  Leaché and Mulcahy (2007) recommended that the Sceloporus magister complex, including the three aforementioned “species”, be considered a single species (S. magister). Those authors also found genetic differences between Arizona and New Mexico “bimaculosus”.  Crother (2017) and the Reptile Database both adopted the recommendation of Schulte et al. (2006), and consider all three separate species.  Phelan and Brattstrom (1955) found individuals in southeastern Arizona with intermediate characters and suggested magister and bimaculosus may interbreed.

Because of the confusion in the taxonomy, and that most museums only label Desert Spiny Lizard specimens as Sceloporus magister, the distribution of the Twin-Spotted Spiny Lizard in Arizona is unclear.  Brennan and Holycross (2006) considered the Twin-Spotted Spiny Lizard a subspecies or form of the Desert Spiny Lizard.  Webb (2009) mapped the distribution of the Twin-spotted Spiny Lizard as extending west to the Whetstone Mountains, south to the border, and north along the border with New Mexico into Graham and Greenlee Counties.  Subspecies maps in Parker (1982) and Stebbins (1985) shows the distribution as being more extensive, extending to north of Tucson.  Leaché and Mulcahy (2007) list bimaculosus specimens from Emery and Lebanon, Graham County; Bowie, Cochise County; Tucson, Pima County; and Roosevelt, Gila County.  Turner et al. (2003) listed S. magister bimaculosus as the only S. magister complex lizard in the Whetstone Mountains, and Corman (1988) considered lizards along the upper San Pedro River to be Twin-spotted Spiny Lizards.  However, lizards farther north on the western Dragoon Bajada appeared to be S. magister (Rorabaugh 2017).  More genetic work needs to be conducted to delineate the ranges of these two species in our area.  Elsewhere, the Twin-spotted Spiny Lizard occurs in southern New Mexico (extending north along the Río Grande) and east and south to southwestern Texas, northern Chihuahua, western Coahuila, and northeastern Durango (Webb 2009).  The species may occur in northeastern Sonora (Rorabaugh and Lemos-Espinal 2016).

This is primarily a species of the Chihuahuan Desert; however its range extends into shrub-invaded semi-desert grasslands at the base of the Whetstone Mountains (Turner et al. 2003) and possibly into Sonoran desertscrub around Tucson and points north.  It occupies low, brushy areas with structural complexity that allow for quick concealment from predators.  This lizard also does well in riparian situations, and can be found perched on rocks, trees, fence posts, and buildings (Corman 1988, Webb 2009, Lemos-Espinal et al. 2015).  At a playa lake in southeastern New Mexico, adult male Twin-spotted Spiny Lizards were always associated with large clumps of mesquite that contained packrat nests and were located on the playa’s edge.  These males did not move among clumps of mesquite, although some females and juveniles did.  The number of adult Twin-spotted Spiny Lizards was predictable from the number of large mesquite clumps that had packrat nests at the base (Whitford and Creusere 1977).  In that study, densities of Twin-spotted Spiny Lizards stayed fairly constant over time, whereas populations of other lizards varied considerably from wet to dry periods.

Most of the natural history studies on the Sceloporus magister complex have been done on species other than the Twin-spotted Spiny Lizard.  However, at a site west of El Paso, male Twin-spotted Spiny Lizards had spermatozoa in the terminal end of the vas deferens from early May through July, indicating the breeding season (Parker and Pianka 1973).  In southeastern New Mexico, activity by the species was bimodal from May through October, with an activity maximum at 0730 hrs (Creusere and Whitford 1982). Seasonally, activity runs from 31 March to 14 November in New Mexico (Degenhardt et al. 1996).  In western Texas, clutch sizes of 3 to 11 are inferred from counts of fertile ova and developing follicles (Axtell 1959).  Minton (1959) noted three size classes in western Texas that he suggested were young of the previous year (about 50 mm SVL), juveniles from two years previous (70-75 mm SVL), and adults that were 95 mm and more SVL.  A hatchling (33 mm SVL) was found on 19 July.  Juveniles that were near hatchling size were found on the Río Conchos, Chihuahua in late August and early September (Smith et al. 1963).  Webb (2009) surmised that both sexes are probably mature at near 80 mm SVL at an age of 21-23 months, although some females are mature in the year after they hatch.  He said that under ideal conditions, eggs hatch in about two months, and hatchlings (30-40 mm SVL) appear from late May into September.  In southeastern New Mexico, Whitford and Creusere (1977) believed Twin-spotted Spiny Lizards fed mostly on ants.  Webb (2009) says the diet consists primarily of insects (especially ants), but also spiders, some plant material, and hatchling lizards.

The IUCN has not evaluated the conservation status of this species.  In Arizona, with a valid hunting license, four Twin-spotted Spiny Lizards can be captured per year or held in possession; however take is prohibited in protected areas such as National Park Service units.  The species is eliminated from urban and agricultural areas; however, there is no reason to believe it is declining in wild or semi-wild areas.

Suggested Reading:

Axtel, B.W. 1959. Amphibians and reptiles of the Black Gap Wildlife Management Area, Brewster County, Texas. The Southwestern Naturalist 4(2):88-109.

Brennan, T.C., and A.T. Holycross. 2006. A Field Guide to Amphibians and Reptiles in Arizona. Arizona Game and Fish Department, Phoenix.

Corman, T. 1988. Abundance, distribution, and habitat management of the reptiles and amphibians of the San Pedro Riparian National Conservation Area. Report to the Bureau of Land Management, San Pedro Project Office, Fairbank, AZ.

Creusere, F.M., and W.G. Whitford. 1982. Temporal and spatial resource partitioning in a Chihuahuan Desert lizard community. Pp. 121-127 in N.J. Scott, Jr. (ed.), Herpetological Communities. U.S. Department of the Interior, Fish and Wildlife Service, Wildlife Research Report 13. Washington D.C.

Degenhardt, W.G., C.W. Painter, and A.H. Price 1996. Amphibians and Reptiles of New Mexico. University of New Mexico Press, Albuquerque.

Fitch, H.S. 1970. Reproductive cycles in lizards and snakes. University of Kansas, Museum of Natural History, Miscellaneous Publications 52:10247.

Leaché, A.D. 2010. Species trees for spiny lizards (Genus Sceloporus): Identifying points of concordance and conflict between nuclear and mitochondrial data. Molecular Phylogenetics and Evolution 54: 162–171.

Leaché, A.D., and J.W.Sites, Jr. 2009. Chromosome evolution and diversification in North American spiny lizards (Genus Sceloporus). Cytogenetic and Genome Research 127: 166-181.

Leaché, A.D., and D.G. Mulcahy. 2007. Phylogeny, divergence times and species limits of spiny lizards (Sceloporus magister species group) in western North American deserts and Baja California. Molecular Ecology 16:5216–5233.

Lemos-Espinal, J.A., H.M. Smith, J.R. Dixon, and A. Cruz. 2015. Anfibios y Reptiles de Sonora, Chihuahua, y Coahuila/Amphibians and Reptiles of Sonora, Chihuahua, and Coahuila. Vols. 1 and 2. CONABIO, Mexico, D.F.

Minton, S.A., Jr. 1959. Observations on amphibians and reptiles of the Big Bend region of Texas. The Southwestern Naturalist 4(3):28-54.

Parker W.S. 1982. Sceloporus magister Hallowell. Desert spiny lizard. Catalogue of American Amphibians and Reptiles (290):1-4.

Parker, W.S., and E.R. Pianka. 1973. Notes on the ecology of the Iguanid lizard, Sceloporus magister. Herpetologica 29(2):143-152.

Phelan, R.L., and B.H. Brattstrom. 1955. Geographic variation in Sceloporus magister. Herpetologica 11(1):1-14.

Rorabaugh, J.C. 2017. Herpetofauna of a 15-hectare parcel on the western bajada of the Dragoon Mountains, Cochise County, Arizona. Sonoran Herpetologist 30(4):72-80.

Rorabaugh, J.C., and J.A. Lemos Espinal. 2016. A Field Guide to the Amphibians and Reptiles of Sonora, Mexico. ECO Herpetological Publishing and Distribution, Rodeo, NM.

Schulte, J.A. II, J.R. Macey, and T.J. Papenfuss. 2006. A genetic perspective on the geographic association of taxa among arid North American lizards of the Sceloporus magistercomplex (Squamata: Iguanidae: Phrynosomatinae). Molecular Phylogenetics and Evolution 39(3):873-880.

Smith, H.M., K.L. Williams, and E.O. Moll. 1963. Herpetological explorations of the Río Conchos, Chihuahua, Mexico. Herpetologica 19(3):205-215.

Turner, D.S., P.A. Holm, E.B. Wirt, and C.R. Schwalbe. 2003. Amphibians and reptiles of the Whetstone Mountains, Arizona. Southwestern Naturalist 48:347-355.

Valdez-Lares, R., R. Muñiz-Martínez, E. Gadsden, G. Aguirre-León, G. Castañeda-Gaytán, and R. Gonzalez-Trápaga. 2013. Checklist of amphibians and reptiles of the state of Durango, México. Check List 9(4):714-724.

Vitt, L.J. 1977. Observations on clutch and egg size and evidence for multiple clutches in some lizards of southwestern United States. Herpetologica 33(3):333-338.

Webb, R.G. 2009. Twin-spotted Spiny Lizard, Sceloporus bimaculosus Phelan and Brattstrom, 1955. Pp. 202-205 in Jones, L.L.C., and R.E. Lovich (eds.), Lizards of the American Southwest: A Photographic Field Guide.  Rio Nuevo Publishers, Tucson, Arizona.

Whitford, W.G., and F.M. Creusere. 1977. Seasonal and yearly fluctuations in Chihuahuan Desert lizard communities. Herpetologica 33(1):54-65.

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