Comparative pollination ecology, fruit and seed set in Corunastylis species (Orchidaceae)

Corunastylis species produce some of the smallest, fly-pollinated flowers of Australian orchids to offer liquid rewards. We observed and collected pollinarium vectors of four Corunastylis species (C. filiformis, C. fimbriata, C. rufa and C. ruppii) with overlapping flowering periods during the summer-autumn months at five sites in New South Wales (NSW), Australia. The most common pollinarium vectors of all species were females of a single morphotype in the genus Conioscinella (Diptera: Chloropidae). This morphotype was less than 3 mm in length and carried dorsal depositions of pollinaria on its thorax. A chloropid could carry as many as two pollinaria and 25-50% of attached pollinia showed erosion, suggesting previous contact with receptive stigmas. Bagging experiments on three species showed low rates of mechanical self-pollination and no fruit set in C. filiformis, C. fimbriata and C. ruppii. The conversion rate of insect-pollinated flowers into fruit varied from 35 to 91% among these three species in NSW versus C. ciliata in Victoria. Seed development also varied with > 42-70% of seeds in the three species in NSW containing fully developed embryos. High levels of reproductive success in these three species in NSW and C. ciliata in Victoria were the same as for fruit sets in other orchid species in other genera with nectar-secreting flowers. As flowering periods, distributions and primary pollinators of four Corunastylis species in NSW overlapped so broadly there appears to be a lack of pre-zygotic interspecific isolation mechanisms. This study provided important pollination and reproductive information towards future conservation management of these orchid species.