Breeding System Evolution in the Arctic: a Comparative Study of Campanula uniflora in Greenland and Iceland

The breeding system and floral development were compared in mid-range (West Greenland) and marginal (North Iceland) populations of Campanula uniflora, a widespread high arctic species which is rare in large parts of its range. Seed set and germination were compared among outcrossed, passively and actively selfed, and control flowers. There were no significant differences in seed set or seed quality among treatments or populations. Seed viability was high and germination rapid following GA3 pretreatment in both populations, but germination was delayed by a week in the Icelandic seeds. The populations showed similar flowering phenology with a short and synchronized flowering period. While the population in Greenland had a floral development typical of the genus Campanula, the Icelandic flowers can be classified as pre-anthesis cleistogamous. Both populations appeared to be predominantly inbreeding, despite being protandrous with pollen released before the flower opened. This method of pollen deposition is interpreted as a secondary mechanism of reproductive assurance, securing seed production. This indicates that an evolutionary switch has occurred, from selection for outbreeding in the ancestral group toward inbreeding in the only truly high arctic species in the genus.