Elegant Earless Lizard (Holbrookia elegans)
Photo by Robert Bezy and Kathryn Bolles
Editor’s note: Also see articles by Larry Jones (Taxonomic turbulence for Holbrookia in southeastern Arizona, and Color patterns of Holbrookia elegans in southeastern Arizona), which appeared in the same issue of Sonoran Herpetologist (December 2010) as the following article.
In August of 1961 I underwent my first field experience with Charles Lowe, an unforgettable adventure into the center of Tohono land, complete with a torrential flash flood and a flat tire without a spare. Our destination was Ventana, an isolated tobosa grassland where we sought the Elegant Earless Lizard (Holbrookia elegans) at the western extremity of its range. This experience added some much-needed enthusiasm to my developing interest in the genus Holbrookia. The previous semester I had studied the relative length of the femur and tibia in various species of sand lizards (Phrynosomatinae) as part of a research project for a course in comparative vertebrate anatomy. From that study and from field work in southeastern Arizona, I had come to realize that two species of lesser earless lizards existed in the state and that they differ in the relative length of the hind limb and the tail, as well as in several other features. I became interested in comparing the morphology, systematics, and biogeography of the Elegant Earless Lizard (Figure 1) and the Common Lesser Earless Lizard (H. maculata).
For various reasons, I eventually abandoned my plans to study lesser earless lizards for my doctoral research. Ralph Axtell had been working on the genus since his masters and doctoral research at the University of Texas, and it seemed wisest to wait until his work appeared in print. Lowe (1964) led the way in recognizing H. elegans as a separate species from H. maculata and provided synopses of their distributions in the state. Yet, the existence of two species of lesser earless lizards in Arizona remained largely ignored until Wilgenbusch and de Queiroz (2000) found that analyses of mitochondrial DNA sequences placed two samples of Holbrookia from Cochise County in widely divergent lineages (gene clades).
The findings of Wilgenbusch and de Queiroz (2000) rekindled my interest in Arizona Holbrookia. Kit Bezy and I collected tissue samples along a transect between populations of H. elegans and H. maculata, securing material to evaluate gene exchange between the two lineages. I also initiated a study of morphological variation, examining specimens of lesser earless lizards from the state in the University of Arizona collection (UAZ).
Since Schmidt’s 1922 review of the genus, the Elegant Earless Lizard has been diagnosed primarily by having a tail length (TL) that is greater than the body length (SVL). This feature is sexually dimorphic, males having relatively longer tails than females. It is further complicated by the large percentage of specimens with incomplete tails (broken or regenerated). Axtell (2009) published a very useful species account of the Elegant Earless Lizard, giving diagnostic features for distinguishing it from the Common Lesser Earless Lizard, summarized here in Table 1. I used Axtell’s color pattern features to assign UAZ specimens to each of the two species. The characters seemed to serve quite well to differentiate the species throughout the state, with a few exceptions detailed below. Specimens of Elegant Earless Lizards identified by color pattern were found to have distinctly longer tails than the Common Lesser Earless Lizard, when males and females are plotted separately, although there is slight overlap and some H. maculata have tails longer than their bodies (Figures 2 and 3). The overlap in relative tail length in part could be due to incorrect species assignments using color pattern, errors in judging tails to be complete, and/or hybridization in areas of species contact. But that at least some of the overlap is due to “biological” (genetic) variation within species is indicated by the existence of specimens H. maculata that are from localities far removed from H. elegans and that have tails longer than their bodies (e.g., Figure 2, E).
I also gathered data for 7 scale characters and for the relative length of the hind limb. All nine characters were entered into a multivariate analysis (discriminant function analysis) with pre-formed groups consisting of specimens of H. elegans and H. maculata that were identified on the basis of color pattern features (Table 1). Additionally, H. maculata was split into a northern group (H. maculata N) and a southern group (H. maculata S) depending on whether the specimens were from north or south of the Mogollon Rim. I encountered difficulty in assigning some individuals from the Huachuca Mountains using color pattern characters, and all specimens from that region were entered as unknowns (i.e., unassigned to group).
The three groups were found to be largely non-overlapping in the resulting plots (Figure 3), consistent with the view that they represent divergent morphological entities. The analyses placed specimens from the Huachuca area in H. elegans, H. maculata, and/or intermediate between the two.
With the exception of the Huachuca and Patagonia mountains, the color pattern characters, relative tail length, and multivariate analyses yield a coherent picture of the geographic distribution of H. elegans (Figure 4). The species ranges from the Ventana grasslands, east across the bajadas of the Quijotoa, Comobabi, Baboquivari, Quinlan, Coyote, Martina, Roskruge, Silverbell, Tortolita, Tucson, Santa Catalina, and Rincon mountains in Pima and Pinal counties; Tumacacori, Pajarito, and Santa Rita mountains in Santa Cruz County; and Whetstone, San Bernardino, and southern Peloncillo mountains in Cochise County. There were two surprising results from the analyses. One is that the Elegant Earless Lizard ranges east to at least the New Mexico border in the area of the San Bernardino National Wildlife Refuge and in Guadalupe Canyon in the Peloncillo Mountains (Figure 4). This finding is consistent with the map presented by Axtell (2009) and with the occurrence of other Sonoran Desert species in the San Bernardino area. The other unanticipated finding is that the one specimen examined from the Verde River valley is clearly assignable to H. elegans (Figures 3 and 4). This is consistent with the occurrence of an isolated pocket of Sonoran Desertscrub in that region (Brown and Lowe 1980). The distribution of H. maculata S below the Mogollon Rim in Arizona is confined largely to the grasslands of the southeastern part of the state: localities near Sonoita, Elgin, Fry, Tombstone, Willcox, and the western and eastern flanks of the Chiricahua and Dos Cabezas mountains, north to the southern bajada of the Winchester Mountains. Above the rim H. maculata N occurs from the New Mexico border west to at least Seligman, Yavapai County (Figure 4).
So what about the Huachucas? Assigning specimens to species from the Huachuca and Patagonia mountains was confounded by the relatively high frequency of a unicolor morph which made scoring individuals for the color pattern features difficult. This unicolor morph is common in these two ranges, and also was seen in a few specimens from the Pajarito and the Tucson mountains. Using all data gathered for the Huachuca area, specimens were assigned to H. maculata from Canelo, Scotia Canyon, Coronado National Memorial, and 10 mi SE Carr Canyon, whereas specimens from Bear Canyon, Sunnyside and some from Scotia Canyon were sufficiently intermediate that I could not assign them to species. All specimens from the Patagonias were assigned to H. elegans, although in some cases this was difficult due to the presence of the unicolor morph and to tail lengths slightly shorter than average for the species.
From the data at hand, I conclude that the Elegant Earless Lizard is one of three morphological units of lesser earless lizards present in Arizona and that the species ranges from the Ventana grasslands east to the New Mexico border in the San Bernardino area, with an apparently isolated population in the Verde River valley. Most individuals of the species can be recognized by their relatively long tail combined with diagnostic color pattern features (Table 1) supplied by Axtell (2009). Some individuals are difficult to assign to species, particularly in the Huachuca and Patagonia mountains where the unicolor morph is common.
The morphological analyses presented here appear to be consistent with the mitochondrial gene tree and distribution map of Blaine (2008; his Figure 2-1) who found that three distinct gene lineages range into Arizona. These appear to correspond with the morphological units recognized above (given in parentheses): “H. thermophila + H. maculata pulchra” (H. elegans), “H. maculata Trans Pecos” (H. maculata S), and “H. maculata Colorado Plateau” (H. maculata N). Clearly additional research is required to understand the distribution and genetic interactions of these three entities in Arizona and elsewhere. Morphological and both mitochondrial and nuclear DNA data are needed at a fine-grained level, with particular attention to zones of contact between the lineages in southeastern Arizona and in the Verde River valley.
As envisioned here, Holbrookia elegans ranges from Arizona south to Sinaloa (type locality, Mazatlán), although Blaine (2008) considers that the northern populations (including those in Arizona) represent a separate species, H. thermophila Barbour 1921 (Sonoran Earless Lizard; type locality, Guaymas).
The Elegant Earless Lizard is known in the U.S. only in Arizona and so it comes as no surprise that research on its ecology and life history is non-existent. Papers on home range (Hulse 1985) and gastrointestinal parasites (Goldberg and Bursey 1992) of Holbrookia populations in Arizona are attributable to H. maculata. For an alternative discussion of variation and systematics of lesser earless lizards in Arizona, see Jones (2010a, 2010b).
The genus was named for John Edwards Holbrook by Girard (1851) who considered Holbrook to be the “father of North American Herpetology” (see Moll 2007). I agree with Moll’s opinion that the English name, “Common Lesser Earless Lizard” is cumbersome, and I have avoided using it in this paper when feasible.
I thank George Bradley for access to specimens in the collection of amphibians and reptiles of the University of Arizona Museum of Natural History; Kit Bezy, Kathryn Bolles, Erik Enderson, Clayton May, and Wade Sherbrooke for participation in field work; Kit Bezy for production of figures; and Kit Bezy and Kathryn Bolles for photography and for helpful suggestions on a previous version of this paper.
Axtell, R. W. 2009. Elegant Earless Lizard, Holbrookia elegans Bocourt, 1874. Pages 150-153 in: L. L. C. Jones and R. E. Lovich (editors). Lizards of the American Southwest. Rio Nuevo Press, Tucson, Arizona.
Blaine, R. A. 2008. Biogeography of the North American Southwest sand lizards. Ph.D. Dissertation. Washington University, Saint Louis, Missouri.
Brown, D. E., and C. H. Lowe. 1980. Biotic communities of the Southwest [map]. General Technical Report RM-78, Rocky Mountain Forest and Experimental Range Station.
Goldberg, S. R., and C. R. Bursey. 1992. Gastrointestinal parasites of the Southwestern Earless Lizard, Cophosaurus texanus scitulus, and the Speckled Earless Lizard, Holbrookia maculata approximans (Phrynosomatidae). Journal of the Helminthological Society of Washington 59:230-231.
Hulse, A. C. 1985. Home range size in Holbrookia maculata (Iguanidae) from southeastern Arizona. The Southwestern Naturalist 30:608-610.
Jones, L. L. C. 2010a. Taxonomic turbulence for Holbrookia in southeastern Arizona. Sonoran Herpetologist 23:170-174.
Jones, L. L. C. 2010b. Color patterns of Holbrookia elegans in southeastern Arizona. Sonoran Herpetologist 23:174-177.
Lowe, C. H. 1964. Amphibians and reptiles of Arizona. Pages 153-174 in: C. H. Lowe (editor). The Vertebrates of Arizona. The University of Arizona Press, Tucson.
Moll, E. O. 2007. Patronyms of the pioneer West XV. Holbrookia maculata Girard, 1851—Common Lesser Earless Lizard. Sonoran Herpetologist 20:26-30.
Schmidt, K. P. 1922. A review of the North American genus of lizards Holbrookia. Bulletin of the American Museum of Natural History 46:709-725 + 1 table and 3 plates.
Wilgenbusch, J., and K. de Queiroz. 2000. Phylogenetic relationships among phrynosomatid sand lizards inferred from mitochondrial DNA sequences generated by heterogeneous evolutionary processes. Systematic Biology 49:592-612.
Author: Robert Bezy
Originally published in the Sonoran Herpetologist 2010 23(12):177-180