Genetic Structure and Outcrossing Rates in Viola pedunculata (Violaceae), a California Endemic Violet Lacking Cleistogamous Flowers

Abstract Although most North American violet species (Viola, Violaceae) produce both showy chasmogamous (CH) flowers and inconspicuous cleistogamous (CL) flowers, some species lack the ability to manufacture the automatically self-pollinated CL flowers. Given that such flowers are considered beneficial as a back-up method of seed production when pollinators are scarce, the ecological and genetic implications of this absence remain unknown. In the current study, we focused on the California endemic violet, Viola pedunculata Torr. & A. Gray, which produces only CH flowers within its habitat in prairies and oak savannahs. Using microsatellites, we quantified the population genetic structure of three mainland populations and one island population in Southern California. We then used allozymes to estimate the outcrossing rate within a single population. Consistent with its production of CH flowers, levels of genetic variation were moderate to substantial within the species (Ap ?=? 6.66, Ho ?=? 0.39), with low but significant structure detected (Θ ?=? 0.11). Furthermore, the high outcrossing rate (0.86) suggests that insect pollinators are frequent enough to ensure adequate seed set. These values were similar to those of a morphologically similar stemmed violet, Viola pubescens Aiton, which produces both CH and CL flowers. Overall, these results are consistent with substantial outcrossing occurring in V. pedunculata through CH flowers, leading to gene flow among populations and potentially counteracting effects of genetic drift.Abstract Although most North American violet species (Viola, Violaceae) produce both showy chasmogamous (CH) flowers and inconspicuous cleistogamous (CL) flowers, some species lack the ability to manufacture the automatically self-pollinated CL flowers. Given that such flowers are considered beneficial as a back-up method of seed production when pollinators are scarce, the ecological and genetic implications of this absence remain unknown. In the current study, we focused on the California endemic violet, Viola pedunculata Torr. & A. Gray, which produces only CH flowers within its habitat in prairies and oak savannahs. Using microsatellites, we quantified the population genetic structure of three mainland populations and one island population in Southern California. We then used allozymes to estimate the outcrossing rate within a single population. Consistent with its production of CH flowers, levels of genetic variation were moderate to substantial within the species (Ap ?=? 6.66, Ho ?=? 0.39), with low but significant structure detected (Θ ?=? 0.11). Furthermore, the high outcrossing rate (0.86) suggests that insect pollinators are frequent enough to ensure adequate seed set. These values were similar to those of a morphologically similar stemmed violet, Viola pubescens Aiton, which produces both CH and CL flowers. Overall, these results are consistent with substantial outcrossing occurring in V. pedunculata through CH flowers, leading to gene flow among populations and potentially counteracting effects of genetic drift.