To buzz or not to buzz: Bee behaviour on Sprengelia (Ericaceae)

Buzz pollination is unusual in the Styphelioideae, Ericaceae. Sprengelia incarnata and S. propinqua have floral characteristics that suggested they might be adapted to buzz pollination, which has been mooted as a transitional stage to wind pollination. To test whether their flowers are adapted for buzz pollination we observed the behaviour of visiting animals and the floral, pollen and scent attributes of both species. We found that S. incarnata is sonicated by five short-tongued native bee species and S. propinqua is groomed by two. The introduced honeybee (Apis mellifera) visited S. propinqua but ignored S. incarnata. The two Sprengelia species have overlapping pollinator profiles, but have diverged enough in their pollen attributes to elicit different behaviours from the same bee species. Sprengelia propinqua has an additional functional group of potential pollinators: represented by the long-tongued A. mellifera. Both species had similar floral scent profiles but S. incarnata had smaller and drier pollen: a necessary pre-adaptation for ambophily and wind pollination.