91 



Fertile hybrids between _C. t. gracilis and _C. Jt. marmoratus are 

 described from an area 1^5 by 65 miles centered on the northern Animas 

 Valley in southwestern New Mexico. Evidence for hybridization is based 

 on color and scutellation characteristics. The ecological distribution 

 of the two subspecies within the study area is described. Hybrids are 

 known from 3 areas; Granite Gap and Steins in the Peloncillo Mountains 

 and in the vicinity of Redrock. The hybrid zone in the Peloncillos is 

 only about one mile wide. Historical factors presumed to influence the 

 described phenomenon are discussed. It is suggested that the two sub- 

 species came into contact during post- Wisconsin times due to the estab- 

 lishment of a desert corridor across the Continental Divide along with 

 expansion of the two taxa from glacial refugia. They are so similar in 

 habitat requirements and adaptations that neither is replaced by the 

 other. Hybrids are produced because of the absence of reproductive 

 isolating mechanisms but hybrid gene combinations are selectively dis- 

 advantagous compared to pure parental types. 



255. — . 1965. Variation in and distribution of the unisexual liz- 

 ard, Cnemido£horustesselat^ AMERICAN MUS. NOVITATES 2235: l-if9. 



This is the classic paper on the species. Its unisexual nature 

 is confirmed, and individual and geographic morphological variation is 

 described in detail. A range map is given. Six pattern classes are 

 described, with greater amounts of ontogenetic change in pattern occur- 

 ring from class A through class F. Pattern classes C and D occur in 

 northeastern New Mexico, sometimes sympatrically, northeast of the 

 Pecos River. Pattern class E occurs throughout the rest of the state, 

 except for two isolated populations in Hidalgo County which are refer- 

 rable to pattern class F. There are places throughout the range of E, 

 for instance Socorro County, where adjacent populations are morphologi- 

 cally different. The existence of multiple clones is suggested. No 

 geographic trends are apparent; variation appears to be random. Varia- 

 tion in 3 scale characters tends to separate classes A-D from E and F. 

 The most striking feature of variation is the relative homogeneity of 

 lizards of class E (geographically the most widespread class) and the 

 diversity of populations occupying the minor remaining part of the spe- 

 cies range. _C. tesselatus shows ranges of variation in pattern and 

 scutellation quite similar to those of widely distributed sexual spe- 

 cies of the genus. When samples from restricted areas are compared, 

 however, tesselatus usually exhibits much less variation than the sex- 

 ual _C. tigris . 



Patterns of evolution in _C. tesselatus are discussed. The appar- 

 ent absence of multiple clones in most local populations is attributed 

 to low mutation rates and/or strong selection for the best-adapted 

 clones to local conditions. Advantages of parthenogenetic reproduction 

 include a higher intrinsic populationai rate of increase compared with 

 a similarily structured sexual population. A parthenogenetic popula- 

 tion consisting of one or a few similar clones that were particularly 

 well-adapted to existing conditions might have an advantage over a sex- 

 ual population that, in effect, sacrificed some of its offspring in 



