92 



more frequent deleterious gene recombinations. But if the parthenogen 

 could not respond quickly enough by genetic adaptation to changing en- 

 vironmental conditions, the population might be at a disadvantage com- 

 pared to a sexual one able more readily to draw upon stored genetic 

 variation. It is suggested that parthenogenetic populations may depend 

 upon, and be able to tolerate, greater mutational rates than sexual po- 

 pulations. There is no evidence that parthenogenetic Cnemidophorus ex- 

 hibit a wider ecological valence than sexual species, which could com- 

 pensate for lower populational potential for genetic change. Pattern 

 type relationships indicate that _C. tesselatus spread from north to 

 south whereas paleoclimatic data indicate just the opposite. The nor- 

 thern part of the species range must have been occupied by it after the 

 termination of Wisconsin glaciation. It is suggested that tesselatus 

 is closely related to _C. tigris or C. septemvittatus, or some other 

 species in the tigris-sexlineatus complex. 



Difficulties in the taxonomic treatment of parthenospecies are 

 briefly discussed. It is suggested that the most reasonable taxonomic 

 choice is to group all of the populations of C. tesselatus into one 

 species; this emphasizes their presumed close relationship and common 

 ancestry. Lizards found at the type locality today belong to class A 

 (which is now known to be triploid) whereas the description of the type 

 material collected in 1820 is of lizards belonging to class D (which is 

 diploid). The closest approach of class D to the type locality today 

 is 70 airline miles to the southeast, and class B (triploid) occupies 

 the intervening area. A diagnosis of _C. tesselatus is provided. Habi- 

 tat is discussed briefly but not well defined. The species is usually 

 but not always found on rocky soils and in roughland habitats from 1500 

 to 5500 feet in elevation. Its distribution is spotty throughout its 

 range and appears to be riparian to a great extent. The habitat of the 

 isolated population in Antelope Pass, Hidalgo County, New Mexico, is 

 described in more detail. It inhabits a sandy desert wash dominated by 

 mesquite and desert willow. 



