FROM POLLINATION BY LEPIDOPTERA TO SELFING - THE CASE OF DIANTHUS-GLACIALIS (CARYOPHYLLACEAE)

Pollination of the alpine herb Dianthus glacialis was studied in a population in the Swiss Alps in 1991 and 1992. Only one insect species, Zygaena exulans (Lepido-ptera), was observed to visit the flowers of D. glacialis. Pollen loads on Z. exulans indicate that it is an effective pollinator of D. glacialis. In 1991, Z. exulans frequently visited flowers of D. glacialis. However, in 1992 almost no visits could be observed. Despite the occurrence of pollinators and the conspicuous flowers of D. 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 other Dianthus 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 in D. glacialis than in outcrossing plants. - Selfing in D. glacialis could have evolved under a shortage of pollinators during the glaciation periods. Present levels of cross-pollination by Z. exulans have apparently not been sufficient to reverse the pollination mechanism of D. glacialis from selfing to outcrossing.