Autonomous Selfing Provides Reproductive Assurance in an Alpine Ginger Roscoea schneideriana (Zingiberaceae)

Abstract

Reproductive assurance, the ability to produce seeds when pollinators or mates are scarce, is thought to be the major advantage of selfing in flowering plants. However, few studies have performed a direct cost-benefit analysis of the selective advantage of selfing, particularly given a long-term perspective among populations or across several flowering seasons within population. This study examined the fertility consequences of autonomous selfing in Roscoea schneideriana (Zingiberaceae), a small perennial Himalayan ginger typically found in habitats at around 3000 m a.s.l. The floral biology of R. schneideriana was studied in natural populations; the capacity for autonomous selfing was estimated using pollinator exclusion experiments; the timing of selfing was quantified by anther removal at different times during flowering; whether autonomous selfing increases seed production was tested by emasculating flowers; and the magnitude of inbreeding depression was estimated by comparing relative performance of progeny from self- and cross-pollinations. Pollinator observations were also conducted in the natural populations. The hooked stigmas of most flowers curl towards the anther and can contact pollen grains at an early stage of anthesis. Flowers with potential pollinators excluded set of as many seeds per fruit as hand-selfed and opened flowers. Autonomous selfing mostly occurs within 2 d of anthesis and can increase seed production by an average of 84 % in four populations during the flowering seasons of 2005-2007. Visits by effective pollinators were extremely rare. The cumulative inbreeding depression of R. schneideriana was 0.226. Autonomous selfing in R. schneideriana is achieved by stigmas curling towards the anthers early in flowering. It is suggested that under the poor pollination conditions, autonomous selfing has been selected for in this alpine ginger because it provides substantial reproductive assurance with very low costs.