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

Pollination of the alpine herb Dianthus glacialis was studied in a pop ulation in the Swiss Alps in 1991 and 1992. Only one insect species, Z ygaena exulans (Lepido-ptera), was observed to visit the flowers of D. glacialis. Pollen loads on Z. exulans indicate that it is an effectiv e pollinator of D. glacialis. In 1991, Z. exulans frequently visited f lowers of D. glacialis. However, in 1992 almost no visits could be obs erved. Despite the occurrence of pollinators and the conspicuous flowe rs of D. glacialis, there are strong indications that this plant is ma inly 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 we ak, (5) seed production by spontaneous selfing is high, (6) seed set i n emasculated flowers is extremely low and (7) the seed/ovule ratio is distinctly higher in D. glacialis than in outcrossing plants. - Selfi ng 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 pollinat ion mechanism of D. glacialis from selfing to outcrossing.