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Discovery of the parthenogenetic Colorado Checkered Whiptail, Aspidoscelis neotesselata (Squamata: Teiidae), in Washington state.

Whiptail lizards of the genus Aspidoscelis (formerly Cnemidophorus; Reeder and others 2002), occur throughout the southern and southwestern United States, with the ranges of some species extending into southeastern Oregon and adjacent Idaho. Throughout their composite range, whiptail lizards are associated with dry, open habitats, particularly desert, grassland, and shrub-steppe (Stebbins 2003). They are diurnal, active, and widely-foraging heliothermic reptiles that prey on invertebrates, and occasionally small vertebrates. Several species of Aspidoscelis are unisexual, comprising solely females, and reproduce by parthenogenesis, a form of asexual reproduction in which offspring are genetically identical to their diploid, triploid, or tetraploid mothers (Wright 1993; Persons and Wright 2009; Lutes and others 2011). Of the 22 currently recognized species of Aspidoscelis found in the United States (Persons and Wright 2009), 11 reproduce parthenogenically (Reeder and others 2002). These populations may occur in limited areas unoccupied by sexual species and in disturbed habitats, but some parthenogenetic species of Aspidoscelis are also widely syntopic with sexual species. In fact, parthenogens that occupy these areas are "weeds" in the botanical sense, thriving in habitats ecologically unavailable to sexual whiptail species (Wright and Lowe 1968). Some unisexual species (for example: Gray-checkered Whiptail, Aspidoscelis dixoni; New Mexico Whiptail, Aspidoscelis neomexicana) are widely distributed, with disjunct populations occurring well outside of their primary range (Manning and others 2005; Cordes and Walker 2006).

In the Pacific Northwest there are 2 species of whiptail lizard, Western Whiptail (Aspidoscelis tigris) and Plateau Striped Whiptail (Aspidoscelis velox). The former is a native bisexual species found throughout North American deserts from southeastern Oregon and southern Idaho, south into mainland Mexico and Baja California (Stebbins 2003). Aspidoscelis velox is an introduced, unisexual species whose natural range is the Colorado Plateau region of northern Arizona, southwestern Colorado, northwestern New Mexico, and southeastern Utah (Stebbins 2003). In the Pacific Northwest, A. velox is known only from Cove Palisades State Park, Jefferson County, Oregon (Nussbaum and others 1983) to which it was probably first introduced in the 1960s (St John 2002).

The Colorado Checkered Whiptail (Aspidoscelis neotesselata) was described in 1997 and is endemic to southeastern Colorado (Walker and others 1997a). Aspidoscelis neotesselata is a parthenogenetic species that originated as the result of hybridization between a diploid unisexual Common Checkered Whiptail (Aspidoscelis tesselata), and a diploid sexual species, Six-lined Racerunner (A. sexlineata). The result of reproduction between a unisexual and a sexual species is an extra set of chromosomes possessed by A. neotesselata, resulting in triploidy. Within the limited natural range of A. neotesselata in a 4-county area, it is known from scattered localities along the Arkansas River and tributaries. Like many other parthenogenetic species, A. neotesselata inhabits disturbed areas such as canyonlands, campgrounds, and heavily grazed pastureland (Walker and others 1997b; Walker and Cordes 1998).


In July 2010, three of us (REW, APO, and JMW) were informed of an unidentified lizard species observed along a northern extension of Lind Coulee south of Moses Lake, Grant County, Washington. Specimens and photographs subsequently obtained at the site were used to identify this species as A. neotesselata. The characters used to identify this population, and eliminate the possibility that it was either A. tesselata or A. tigris, are apparent in Figure 1. In the dorsal view of a captive juvenile (Fig. 1, top left), important distinguishing characters include: the black fields (ground color) between the pale-colored stripes; the 3 complete and distinct primary stripes on both sides of the body; the pale vertebral "line" between the paravertebral stripes that is interrupted along its length; the extensions of the dorsolateral and paravertebral stripes on the basal region of the tail; the pale incipient spots above the lateral (lower) stripe on each side of the body; and the pale incipient bars below the lateral stripe on each side of the body. In the dorsal view of an in situ adult female (Fig. 1, top right), important distinguishing characters include: the black fields (ground color) between the pale-colored stripes; the 3 intact primary stripes on both sides of the body that are either coalesced with or closely associated with pale spots and vertical bars; the vertebral line between the paravertebral stripes represented by a linear series of dashes; the extensions of the dorsolateral and paravertebral stripes on the basal region of the tail; the vertical bars on the sides of the body crossing the lateral stripes; and the profusion of spots on the upper part of the body. In the ventral views of a captive adult female (Fig. 1, bottom left and right), important distinguishing characters include: the white ground color; the black-edged lateral abdominal scale rows; the enlarged mesoptychial scales bordering the gular fold; and the unbroken white bar on the posterior surface of each thigh.

We used subsequent visits to the Grant County site to document that this population of A. neotesselata comprises numerous adults, subadults, and juveniles (including recent hatchlings). The area where these lizards were observed is bisected by a dirt-gravel road running north-south along a canal flowing into Lind Coulee; and north of the site, agricultural fields border either side of the road. Large quantities of discarded objects and garbage are present at the site, and in some cases carpet strips and discarded tires serve as cover for lizards. The vegetation in the upland area along the west side of the site consists of remnants of native Big Sagebrush (Artemisia tridentata) and Green Rabbitbrush (Chrysothanmus naseosus), and large amounts of introduced weed species, primarily Bromus spp. and Centaurea spp. Near the water, Salix spp. is dominant, with a thick understory of unidentified non-native weeds that forms a tangle of vegetation that serves as retreat areas for the lizards. Numerous burrows are located along the banks of the canal, and lizards were observed at the entrances of, as well as entering, these burrows. Other species of reptiles observed at the site were North American Racer (Coluber constrictor) and Gophersnake (Pituophis catenifer); neither was abundant.

Sixteen trips to search for these lizards were made by REW and others from late July through October 2010. During initial visits, individuals of A. neotesselata were readily observed from 12:00 to 19:30 (PST), at air temperatures exceeding 35[degrees]C. During the hottest times of day, adults were observed foraging under heavy foliage near water. Earlier or later in the day, lizards were observed in the open, moving between shrubs. Body temperatures of 3 adults recorded on a 3rd trip in August ranged from 33 to 36[degrees]C.

Aside from the capture of a juvenile and an adult for photographs, no effort was made to obtain samples of A. neotesselata for preservation and analysis during these first few visits. Some census counts were attempted, but we were unable to differentiate between individuals. During our 1st visit, however, 33 lizards were observed, and during subsequent visits we observed >100 lizards. Our initial collection efforts met with limited success because lizards were difficult to collect alive. During later trips, large (1.27 cm width) rubber bands were used to stun or kill a small number of adults and hatchlings. These specimens have been cataloged (CWU # 1693-1703), and deposited into the herpetology collection at Central Washington University, Ellensburg, Washington. Future specimens will also be deposited into collections at the University of Arkansas.

During September, we made 3 trips, with few adults observed. In contrast, we observed several hatchlings (some collected) throughout the day. The few adult lizards were observed when substrate temperatures were >25[degrees]C. Our last trips were made mid-October, with no adults, and only 4 hatchlings observed. During these later trips, we made attempts to locate lizards away from the main site. As we moved south along the dirt road, lizard sightings decreased. This road bisects State Route (SR) 243 <1 km south of the main site, and no lizards were observed in this area. To the west, Road M SE runs parallel to the site, and several agricultural fields are present to the west. No lizards were observed during our survey to the west of the site.

Additional observations of A. neotesselata at areas away from the main site have also been reported by others to Washington Department of Fish and Wildlife (WDFW) biologists. One site was a boat launch on Lind Coulee, south along Road M SE. Other observations were from a site along Frenchman Hill Wasteway, west of the main site. The former site is similar to the main site in being a fragmented, disturbed patch of shrub-steppe, while the latter is a more intact area of shrub-steppe with few invasive plant species. No individuals of A. neotesselata were observed during 12 visits to these sites by REW (and others), so it remains unconfirmed that populations of the species exist away from the main site.

Discovery of A. neotesselata in Grant County, Washington, could not be more unexpected. This triploid species, endemic to southeastern Colorado east of the Continental Divide, arguably has one of the smallest natural ranges among parthenogenetic species of Aspidoscelis (Walker and others 1997a, b). The population of A. neotesselata reported herein establishes its presence more than 1600 km northwest of its natural distribution area. We are inclined to believe that its presence in Grant County is the result of an accidental introduction in an interstitial tract of waste land in an area extensively used for agriculture. Moreover, there is little doubt that parthenogenetic reproduction in A. neotesselata facilitated its introduction to Grant County, which theoretically required only a single egg, juvenile individual, or adult lizard. In subsequent studies, we will analyze diet preferences, reproductive characteristics, karyotypes, and morphological variation in this intriguing Washington adventive species.

Key words: Aspidoscelis neotesselata, Colorado Checkered Whiptail, Grant County, Lind Coulee, Teiidae, Washington State

Acknowledgments.--We thank the Snow family of Moses Lake, Washington, for informing us of this previously unknown population of lizards. Involvement of JMW in this project resulted from information received from G Manning. We thank M Hayes (WDFW) for discussions on this topic. Lastly, we thank D Darda for assistance in collecting lizards.


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Department of Biological Sciences, Central Washington University, Ellensburg, WA 98926; weaverro@ (REW); 15319 Ash Way #e4, Lynwood, WA 98087 (APO); 4112 Rechet Court, Olympia, WA 98501 (JLW); Frontier Middle School, 517 West 3rd Ave, Moses Lake, WA 98837 (JMK); Department of Biological Sciences, University of Arkansas, Fayetteville, AR 72701 (JMW);; Submitted 11 April 2011, accepted 31 May 2011. Corresponding Editor: Gary Fellers.
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Title Annotation:GENERAL NOTES
Author:Weaver, Robert E.; O'Connor, Andy P.; Wallace, Joshua L.; King, Jeffrey M.; Walker, James M.
Publication:Northwestern Naturalist: A Journal of Vertebrate Biology
Date:Dec 22, 2011
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