Baum, Donoghue, and Davis Malpighiaceae are a family of flowering plants that are an important element of forests and savannas in the Old and New World tropics. New World Malpighiaceae are pollinated by specialized oil-collecting bees (anthophorid females) and exhibit a highly conserved floral morphology despite tremendous diversity in fruit morphology and habit. These oil-collecting bees are absent from the Old World. Some Old World clades, like Acridocarpus, are presumed to be derived from New World lineages and they exhibit a combination of features associated with oil-bee pollination and with "buzz" pollination. These groups provide an opportunity to examine the consequences of the loss of specialized pollinators. The goals of this study by graduate student Charles Davis, under the direction of Drs. David Baum and Michael Donoghue, are (1) to infer the phylogenetic relationships within Malpighiaceae using chloroplast and nuclear DNA sequences, (2) to infer the phylogeny or genealogy of Acridocarpus species in order to examine patterns of floral morphological evolution associated with pollinator shifts, and (3) to document the pollination of Acridocarpus in African habitats. Preliminary molecular data indicate that Old World genera of Malpighiaceae belong to several separate lineages, suggesting that morphologies associated with buzz pollination have evolved more than once independently. However, several areas of the phylogeny remain poorly resolved. Furthermore, several additional Old World lineages need to be added to existing datasets. Analyses of Acridocarpus using ribosomal DNA sequences reveal two major clades, one including species endemic to Madagascar and New Caledonia and the other consisting of species distributed across Africa. Oil glands appear to be entirely absent in species from Madagascar and New Caledonia, but appear in some African species. Fieldwork in Africa indicates that species of Acridocarpus are pollinated by large xylocopine bees that buzz the anthers, and the floral glands produce sugars rather than oils. Resolving the phylogeny of Malpighiaceae with additional chloroplast DNA sequences, along with sequences of a nuclear phytochrome gene, will clarify the origin and relationships of the Old World species. Further phylogenetic work will allow an evaluation of whether Old World species with similar morphologies have evolved independently, and whether such floral evolution is associated with the loss of oil-collecting pollinators. This study will shed light on the patterns and mechanisms of morphological change following a shift in pollination system.
