Dioecy and wind pollination in Pernettya rigida (Ericaceae) of the Juan Fernandez Islands

Pernettya rigida is endemic to the Juan Fernandez archipelago. Although all flowers are complete, with seemingly fertile stamens and pistils, differen ces in fruit production and detailed field. anatomical, and morphological s tudies indicate they are functionally unisexual, and the species is consequ ently dioecious. A comparison of 15 features demonstrated significant diffe rences between the sexes. The populational sex ratio is 1:1. Nectaries loca ted between the filaments produce small amounts of floral nectar with simil ar sugar composition in both sexes. There are x = 33,357 (or x = 133,429) p ollen tetrads (or pollen grains)/male flower and x = 109 ovules/female flow er. No tetrads in either hand self-pollinated or open pollinated male flowe rs showed any pollen germination. Tetrads on open- and hand-pollinated fema le flowers germinate. Female flowers do not show autogamy or apomixis. Duri ng more than 80 hours of field observation, we recorded only seven floral v isitors (representing three insect species). In spite of this, open-pollina ted female flowers have abundant fruit and seed-set. Thus, we conclude that pollen is transferred abiotically and the ever-present wind over the expos ed ridges of the islands is the likely dispersal agent. A number of anemoph ilous features, such as dry pollen and exposed habitat, support this conclu sion. Thus, dioecy and anemophily hale evolved independently, in situ, in t his species in this remote locality. Preservation of habitat and eliminatio n of competitive invasives are the primary conservation challenges. (C) 200 0 The Linnean Society of London.