Department of Biology
Phenotypic Variability of Physiological Traits in Populations of Sexual versus Asexual Whiptail Lizards (Genus Cnemidophorus)
Alistair J. Cullum
Department of Ecology and Evolutionary Biology
University of California, Irvine
Irvine, CA 92697-2525
Evolutionary Ecology Research 2(7):841-855 (2000)
Abstract - One of the major potential disadvantages to asexual reproduction is believed to be a reduction in phenotypic variability. The actual consequences of apomictic reproduction for population variability have rarely been studied, however. In this study, I examine the variance of physiological traits in parthenogenetic species of the lizard genus Cnemidophorus. Five whole-organism physiological traits (burst speed, endurance, maximal exertion, standard metabolic rate and evaporative water loss rate) were examined in four asexual species and the sexual species that hybridized to produce them. Trait variances for sexual and asexual species were compared using a phylogenetically-controlled approach appropriate to hybrid-parental comparisons. The analysis revealed lower levels of trait variance in asexual species for the first three traits, but no detectable differences between asexual and sexual species for the other two traits. A second analysis examined the influence of each populations maximum and minimum value on overall population variability, and revealed that, on average, the variances of sexual populations were more heavily influenced by outliers than were asexual ones. These results suggest that part of the reason for increased variance in sexual populations may be a greater tendency for these populations to produce extreme phenotypes.