[Ann Sakai] [Stephen Weller] [Research-Dioecy] [Research-Heterostyly] [Research-Conservation]
Sakai/Weller Lab

Evolution of plant breeding systems: Dioecy

Schiedea verticillata. Photo by Nobumitsu Kawakubo
Schiedea obovata. Photo by Nobumitsu Kawakubo
Scheidea hookeri. Photo by Nobumitsu Kawakubo

Evolution of dioecy.  Most plants are hermaphroditic, with both male function (with pollen and stamens) and female function (with ovules, pistils, seeds, and fruit) in each flower.  About 6% of flowering plant species are dioecious (unisexual plants with male flowers or female flowers in the population). The Hawaiian Islands are particularly rich in dioecious species; about 15% of native Hawaiian flowering plant species are dioecious.  Why has dioecy evolved?  A combination of high selfing rates and high inbreeding depression may have promoted strong selection for outcrossing mechanisms such as dioecy.  Differences in allocation to male and female function that lead to accelerating fitness gains may also promote separate sexes. 

Multi-disciplinary approach. We have used a multi-disciplinary approach (e.g., phylogenetic analyses, field studies of pollination biology, greenhouse crossing programs for genetics, physiological studies, quantitative genetics) to investigate factors important in the evolution of breeding systems in the native Hawaiian genus Schiedea (Caryophyllaceae, carnation family), one of the largest lineages in the native Hawaiian flora.  In several species, the presence of both high selfing rates and high levels of inbreeding depression suggest that some species have unstable breeding systems.  Changes in allocation to male and female function have also occurred, and these changes appear to be related to changes in habitat.  Shifts from hermaphroditism to gynodioecy or dioecy usually are accompanied by a shift from mesic or wet habitat to dry windy habitats, along with the evolution of wind pollination.

Current research. In collaboration with Diane Campbell (University of California-Irvine), we are investigating the genetic potential for changes in biomass allocation to male and female function in two gynodioecious species of Schiedea. In this quantitative genetics study, we are examining the heritabilities and genetic correlations of biomass as well as related morphological and physiological traits. We are also conducting an artificial selection experiment, examining how these traits change with selection for greater stamen biomass in hermaphrodites or greater female biomass in females. 

Monoecy. Graduate student Laura Vary is interested in the evolution of plant breeding systems in island ecosystems.  She is investigating breeding systems in the flora of Madagascar and factors affecting the incidence of monoecy in this unique flora.