Does habitat disturbance promote geographical parthenogenesis in whiptail lizards?

Sexual and asexual organisms often vary in their distribution and abundances among habitats. These patterns of “geographical parthenogenesis” can shed light on ecological conditions underlying the evolution of sex. Habitat disturbance is hypothesized to be a mechanism that generates geographical parthenogenesis. Parthenogens are predicted to be more prevalent in disturbed habitats than sexuals due to the greater colonizing ability of parthenogens and the tendency of parthenogens to avoid competition with sexuals in undisturbed habitat. We tested whether habitat disturbance (i.e., a rapid state transition between vegetation communities) causes geographical parthenogenesis in whiptail lizards in the Chihuahuan Desert of southern New Mexico. Non-experimental approaches have shown the parthenogenetic Aspidoscelis uniparens commonly occurs in habitat with a history of vegetation disturbance from shrub removal, whereas the sexual A. marmorata occurs more often in undisturbed shrubland habitat. We used a field experiment replicated across 16 sites to test whether the parthenogen A. uniparens and sexual A. marmorata differ in their response to vegetation disturbance from shrub removal. The sites were distributed across a broad region of southern New Mexico, and we used a paired design with each site including a shrub-removal treatment and a control on 9-ha plots. Using a co-abundance model that accounts for imperfect detection, we found the parthenogen A. uniparens and sexual A. marmorata both responded positively to disturbance, but only when the congener was rare. Our results are inconsistent with the idea that parthenogens exploit disturbed habitat to avoid competition with sexuals. In our study system, A. uniparens often dominates older disturbed sites, especially two decades or more after shrub removal. Collectively, these results indicate geographical parthenogenesis emerges from biotic interactions in heterogeneous landscapes that include disturbed habitats used by sexual and asexual species alike.