East of the Rocky Mountains in Colorado, gonochoristic (Tomlinson, 1968) Aspidoscelis sexlineata is distributed widely, whereas parthenogenetic A. tesselata (pattern class C) has been recorded from relatively small areas of only three southeastern counties (Walker et al., 1997; Hammerson, 1999). Distributions of these lizards in Colorado reflect different tolerances for climatic, edaphic, topographic, and vegetational variables (walker et al., l998), largely stemming from different modes of evolutionary origin. Derivation of the allodiploid genome of A. tesselata in either northern Mexico or southern Texas from A. tigris marmorata X A. gularis septemvittata (Neaves, 1969; Parker and Selander, 1976; Dessauer and Cole, 1989) did not hamper its dispersal northward to otero and Las Animas counties, Colorado (Parker and Selander, 1976). However, lack of further expansion northward, based largely on this allodiploid genome, coincides with northwestward dispersal of Aspidoscelis neotesselata, a triploid parthenogenetic species of recent origin from A. tesselata X A. sexlineata (Parker and Selander, 1976; Densmore et al., 1989), beyond the range of A. tesselata into pueblo and Fremont counties (walker et al., 1997; Taylor et al., 2006). Coexistence of A. tesselata C and A. sexlineata in southeastern Colorado provided an opportunity to compare diets between congeners with strikingly different reproductive modes, size of adults, and evolutionary histories. our study addressed the following questions: Do syntopic populations of A. tesselata C and A. sexlineata have similar breadths of diet? Does breadth of diet change across months and years? Are there significant differences between observed dietary overlaps and overlaps predicted by chance? Are breadths of diets of A. tesselata C and A. sexlineata in Colorado similar to those reported for A. tesselata E and different gonochoristic congeners in Trans-Pecos, Texas (Schall, 1993)?