Mixed-Mating Strategies and their Sensitivity to Abiotic Variation in Viola Lanceolata L. (Violaceae)

Mating-system expression is sensitive to environmental conditions, and can be an important determinant of lifetime fitness because progeny that are produced via outcrossing vs. selfing may differ in quality. We quantified sexual and asexual reproduction in Viola lanceolata, a regionally threatened species, across populations that varied in disturbance history and across microsites that differed in percent soil moisture, irradiance, and temperature. In V. lanceolata, reproduction can occur sexually through facultatively outcrossing chasmogamous (CH) flowers and obligately selfing cleistogamous (CL) flowers in addition to asexually via stolons. The frequency of individuals producing CH and CL flowers differed among sites as did the frequency of vegetative reproduction. Interestingly, sites also differed in fruit maturation success, with ~33, 100, and 16% of the CH fruits matured in the oldest, intermediate, and most-recently disturbed populations respectively. Analogous site differences in CL fruit maturation were observed. Cleistagamous, but not CH, reproduction was also dependent on percent soil moisture. The observed differences in fruit maturation success likely lead to variable rates of outcrossed vs. self-fertilized seed production; as a consequence, populations are likely to differ in genetic structure and in relative dependence on chasmogamy vs. cleiostogamy for population growth. Finally, CL flower and stolon production were negatively correlated, suggesting a tradeoff between sexual and asexual reproduction that might affect population growth.