Comparative floral presentation and bee-pollination in two Sprengelia species (Ericaceae)

Pollination by sonication is unusual in the Styphelioideae, family Ericaceae. Sprengelia incarnata and Sprengelia propinqua have floral characteristics that suggested they might be adapted to buzz pollination. Both species have florally similar nectarless flowers except that the stamens of Sprengelia propinqua spread widely after the flower opens, while those of Sprengelia incarnata cohere in the centre of the flower. To test whether sonication occurs, we observed bee behaviour at the flowers of both plant species, documented potential pollinators, and examined their floral and pollen attributes. We found that Sprengelia incarnata had smaller and drier pollen than Sprengelia propinqua. We found that Sprengelia incarnata was sonicated by native bees in the families Apidae (Exoneura), Halictidae (Lasioglossum) and Colletidae (Leioproctus, Euryglossa). Sprengelia propinqua was also visited by bees from the Apidae (Exoneura) and Halictidae (Lasioglossum), but pollen was collected by scraping. The introduced Apis mellifera (Apidae) foraged at Sprengelia propinqua but ignored Sprengelia incarnata. The two Sprengelia species shared some genera of potential pollinators, but appeared to have diverged enough in their floral and pollen characters to elicit different behaviours from the native and introduced bees.