Differences in floral traits and flower visitation rates in mating systems in Prunella vulgaris (Lamiaceae)

Abstract

Abstract Aims Floral traits and the number of visitors are expected to change with different mating systems. We tested this hypothesis by comparing flowers of Prunella vulgaris (Lamiaceae) with inserted and exserted styles across a strongly exserted style biased, an exserted style biased, and a strongly inserted style biased subalpine population. Methods We examined flowering phenology, floral morphology, flower visitation rate, capacity for autonomous self-pollination, and visitor contribution to seed production for each style type and in each population. We also examined inbreeding depression by comparing the relative performance of progeny from self- and cross-pollination. Important Findings Exserted style plants had larger and more open flowers, increased pollen production, higher amounts of nectar rewards, and higher visitation and outcrossing rates than inserted style plants. Similarly on the population level, the visitation rates were higher in the exserted style biased populations than in the inserted style biased population. Inserted style plants provided a stronger reproductive assurance through autonomous selfing than exserted style plants. Reproductive assurance and outcrossing rates did not differ among populations, showing low visitation rates may be sufficient for adequate seed production in P. vulgaris. Although inserted style plants had a lower inbreeding depression level than exserted style plants, the inbreeding depression of both was less than 0.5, suggesting that an inbreeding depression should not counteract the evolution of selfing in this species. Inserted style plants provide reproductive assurance through autonomous selfing, and exserted style plants ensure outcrossing through pollinator services, supporting a stable mixed mating system in this subalpine plant.