Reproductive Strategies in Sympatric Whiptail Lizards (Cnemidophorus): Two Parthenogenetic and Three Bisexual Species

Abstract

Reproductive characteristics in five sympatric Cnemidophorus species were similar. All were multi-brooded with small clutches and low clutch weight/body weight ratios, an estimate of reproductive effort (RE). Interspecific differences in mean clutch sizes and egg weights are attributed partially to female body size differences. RE varies interspecifically perhaps as a result of differential habitat productivity. Intraspecifically, clutch size but not RE was positively correlated with body size. Intraspecific RE variation patterns differ among species. Egg weight-body weight correlation was not significant for the four larger species; however, egg weight was positively correlated with body weight in the smallest species. Smaller species also produced relatively larger eggs. A minimum egg size in Cnemidophorus is suggested. Whiptail RE's are difficult to measure because important costs such as courtship, mating, carrying eggs and locating suitable nest sites are not easily quantified. The reproductive cycle is similar in all species. Males emerge from brumation with enlarged testes which decrease in volume throughout the summer. Females emerge with yolked follicles. Fat bodies are small in in both sexes early in the season, continue to drop during the summer, and rebuild after reproduction ceases. Males possess femoral pegs most commonly during the reproductive season. No difference between bisexual and parthenogenetic species was observed. Unisexual species may simply resemble one of their bisexual parental species. Cnemidophorus reproductive characteristics depend on their body size and ecological position as fast moving, widely foraging species. Such factors could overshadow differential selection operating on the reproductive characteristics of weedy parthenogenetic and nonweedy bisexual species.