Minisymposium 17: Evolution of Plant Development

Abs # 31001: The Hawaiian Islands: a model environment for molecular studies of flower and fruit evolution

Presenter:	Albert, Victor A., victor.albert@nhm.uio.no
Authors	Albert, Victor A. (A)   Lindqvist, Charlotte  (A)
Affiliations:	(A): Natural History Museums and Botanical Garden, University of Oslo, Norway

The Hawaiian Islands, with their extreme isolation and young geological age, provide an ideal setting for comparative research on the processes underlying plant reproductive evolution. Although many Hawaiian plant groups display considerable morphological diversification, these radiations are usually contrasted with poor genetic divergence. Several examples of in situ evolution of reproductive features have been discerned from the limited phylogenetic studies available. Breeding system (hermaphroditism to dioecy) and pollination syndrome (biotic to wind) evolution have been characterized in the endemic Alsinoideae (Caryophyllaceae). Studies of model Caryophyllaceae (Silene) have uncovered gene products active during sex determination that might serve as tools for investigating the diverse Alsinoideae. Bird pollination has evolved within other Hawaiian endemics, e.g., in Stenogyne (Lamiaceae) and species of Geranium (Geraniaceae) and Hibiscadelphus (Malvaceae). QTL studies, which in Mimulus (Scrophulariaceae) suggest that only few genes of large effect may be critical for premating isolation between bird vs. insect pollinated species, could be attempted with these taxa. Floral homeosis is known in the endemic genus Clermontia (Campanulaceae), of which 2/3 of species have a second whorl of petals replacing sepals. Molecular phylogenetic studies suggest a single origin of the trait, possibly as recently as 3.7 Mya, followed by one or few reversals to wild type. Earlier research has demonstrated expression of a PISTILLATA ortholog in whorl 1 of such species. However, the double-corolla lesion could be within a B-function coding sequence, its promoter, or even in an upstream regulator. Clermontia and some other Hawaiian lobelioids bear fleshy berries, whereas the ancestral state is dry capsules. Stenogyne also bears fleshy fruits, rather unlike its dry-fruited ancestors. The difference appears to lie during differentiation, which in the dry-fruited taxa may involve apoptotic factors already identified in model systems. Finally, superior ovaries have evolved inside the endemic genus Tetraplasandra of the otherwise epigynous family Araliaceae. This morphological change occurs late in ontogeny, after carpel identity is established. These recent and genetically narrow reproductive shifts could provide excellent systems for comparative molecular studies of morphological ‘macro’evolution. Supported in part by The Floral Genome Project, NSF DBI-0115684.