Distribution and Habitat of the Parthenogenetic Whiptail Lizard, Cnemidophorus laredoensis (Sauria: Teiidae)

Abstract

The parthenogenetic whiptail lizard Cnemidophorus laredoensis, an apparent cloned hybrid species, had been reported from only two localities in southern Laredo, Webb Co., Texas, and none in Mexico when this study was initiated in 1983. This report lists totals of 25 (23 new) localities in Dimmit, LaSalle, Webb, Zapata, Starr and Hidalgo counties, Texas, and 11 in Tamaulipas State, Mexico. Cnemidophorus laredoensis was found in syntopy with its apparent maternal progenitor C. gularis at 19 localities in Texas and six in Tamaulipas. Unlike many parthenogenetic species of Cnemidophorus which extend the range of the genus into geographic areas and habitats not inhabited by gonochoristic species, the range of C. laredoensis is entirely contained within the much more extensive range of C. gularis. Although most locality records for C. laredoensis are located within a narrow riverine zone of ca. 10 km in width and 250 road km in length on both sides of the Rio Grande between Nuevo LaredoLaredo and Nuevo Progreso-Progreso Lakes, the species also occurs well away from the Rio Grande in parts of Dimmit, LaSalle and Starr counties. The habitats of C. laredoensis vary from slightly altered to radically disturbed sites with sandy to loamy soil which support short or tall grass-weed, weed-mesquite, bunchgrass-mesquite and/or ecotonal thorn shrub assemblages. The Laredo whiptail is frequently found in habitats which have been subjected to catastrophic alteration, long-term degradation or significant changes leading to the virtual absence of C. gularis at some sites. Cnemidophorus laredoensis is less likely to be excluded from extensively altered habitats than C. gularis, since each individual of the former is capable of producing eggs which develop parthenogenetically. INTRODUCTION The Laredo whiptail lizard Cnemidophorus laredoensis possesses a number of biological attributes which make it a most unusual and compelling subject for research. It is an all-female parthenogenetic species, one of less than 2 dozen such forms among all of the vertebrates, which was apparently generated through an instance of hybridization between the gonochoristic species C. gularis and C. sexlineatus. Cnemidophorus laredoensis is also remarkable in its restricted latitudinal range, syntopic to closely parapatric relationship to one of its parental species, C. gularis, throughout its range and geographical distribution which is well E of all other parthenogenetic species of Cnemidophorus. At the initiation of this study in 1983, parthenogenetic whiptail lizards (genus Cnemidophorus) had been reported from only two localities in Texas and none in Mexico in the vast expanse of the Rio Grande Valley between the mouth of the Pecos River and the Gulf of Mexico. The first specimens of Cnemidophorus laredoensis were collected in 1970 at Chacon Creek Arroyo, Laredo, Webb Co., and at the time of collection were thought to represent the gonochoristic species Cnemidophorus gularis which is widely distributed in Webb Co. (McKinney et al., 1973). That an undescribed all-female population occurred at Chacon Arroyo was first indicated by the unusual number of females in the 1970 sample and the high frequency of heterozygosity at some gene loci as determined by electrophoresis (McKinney et al., 1973). The subsequent description of C. laredoensis was based upon two series of specimens collected only 1.6 km apart in the suburban clutter of southern Laredo and included no information on the habitat of the species or its relationship to C. gularis and C. sexlineatus. Aside from subsequent papers by Bickham et al. (1976) establishing that C. laredoensis is allodiploid (2n = 46) with one genome from each of its gonochoristic progenitors and Wright et al. (1983), identifying