From pollination byLepidoptera to selfing: The case ofDianthus glacialis (Caryophyllaceae)

Pollination of the alpine herbDianthus glacialis was studied in a population in the Swiss Alps in 1991 and 1992. Only one insect species,Zygaena exulans (Lepidoptera), was observed to visit the flowers ofD. glacialis. Pollen loads onZ. exulans indicate that it is an effective pollinator ofD. glacialis. In 1991,Z. exulans frequently visited flowers ofD. glacialis. However, in 1992 almost no visits could be observed. Despite the occurrence of pollinators and the conspicuous flowers ofD. glacialis, there are strong indications that this plant is mainly selfing: (1) anthesis of individual flowers is short (c. one and a half days), (2) protandry, although pronounced in otherDianthus spp., is absent, (3) nectar production is low, (4) odour production is weak, (5) seed production by spontaneous selfing is high, (6) seed set in emasculated flowers is extremely low and (7) the seed/ovule ratio is distinctly higher inD. glacialis than in outcrossing plants.—Selfing inD. glacialis could have evolved under a shortage of pollinators during the glaciation periods. Present levels of cross-pollination byZ. exulans have apparently not been sufficient to reverse the pollination mechanism ofD. glacialis from selfing to outcrossing.