Evolution of plant breeding systems:
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 with unisexual male flowers on some plants and unisexual female flowers on other plants in the population. The Hawaiian Islands are particularly rich in dioecious species; about 15% of native Hawaiian flowering plant species are dioecious. What factors favor the evolution of dioecy? These factors may include a combination of high selfing rates and high inbreeding depression promoting outcrossing mechanisms (such as dioecy) as well as differences in resource allocation patterns of males and females. We have used the native Hawaiian genus Schiedea (Caryophyllaceae, carnation family) as a model system to investigate these factors in the evolution of breeding systems, including dioecy. Our earlier work based on a morphological and molecular phylogeny of this group (in collaboration with Warren L. Wagner, Smithsonian Institution, and Doug and Pamela Soltis, University of Florida), suggests that hermaphroditism is the ancestral condition within this lineage of 33 taxa. Based on our work as well as the work of a number of undergraduate and graduate student researchers in our lab, it appears that in many cases, gynodioecy (females and hermaphrodites in populations) and dioecy are favored by a combination of high selfing rates and high levels of inbreeding depression. Changes in allocation patterns to male and female function have also occurred. These changes in breeding system are also coupled with changes from a wet to dry habitat, and from biotic to wind pollination. For more detailed information, please see selected references. In related research, Stephen Weller and César Domínguez are studying the evolution of distyly from tristyly in Oxalis alpina, species that is distributed across Mexico and the American Southwest.
Our current research is a collaboration with Diane Campbell (University of California-Irvine), postdoctoral researcher Theresa Culley and technician Amy Dunbar. We are investigating the genetic basis of resource allocation patterns to male and female function in two gynodioecious species of Schiedea (see photo above showing gynodioecious Schiedea salicaria with hermaphroditic flowers on the left and female flowers on the right). This includes a five year quantitative genetics study of the potential for genetic changes in allocation patterns to male and female function. We are examining the heritability and genetic correlations of morphological and developmental characters, as well as physiological traits related to water use efficiency and photosynthesis. We are currently collaborating with Todd Dawson (University of California-Berkeley) in studies to understand how water use efficiency and phyotosynthetic capacity have changed in a phylogenetic context with changes in habitat and with the differentiation of the sexes. In other research in our lab, undergraduate Lisa Kunzman is investigating details of the degree of dominance in the genetics of sex expression in this system. Graduate students in our lab have also pursued interests in plant breeding system evolution. Graduate student Syndallas Baughman has investigated changes in resource allocation in wild strawberry (Fragaria virginia) in the Sierra Nevada, and graduate student Camille Barr has been investigating the impact of sex ratio variation in a California native, baby blue-eyes (Nemophila menziesii).
The Hawaiian Islands have one of the highest proportions of rare and
endangered species in the United States, and it is impossible to ignore
the degradation of the environment through habitat loss, and impacts of
feral animals and invasive species. Our research also has an applied
component addressing some of these issues in conservation biology.
In collaboration with Warren L. Wagner, Dr. Sakai is working on ecological
correlates and phylogenetic patterns of endangerment in the native Hawaiian
flora. Dr. Weller, in collaboration with Dr. Robert Cabin (SUNY-Plattsburgh)
and Dr. David Lorence (National Tropical Botanical Garden) has worked
for a number of years on the impact of fountain grass (Pennisetum setaceum)
on dry forest sites on the island of Hawaii. They are also monitoring
community changes with exclusion of large herbivores on mesic forests
of Kauai. Drs. Sakai and Weller have been instrumental in setting
up the Collaboratory on the Population Biology of Invasive Species, a
working group funded by the National Science Foundation to better integrate
basic research ideas in population biology with the more applied needs
of managers. This group sponsored a workshop in Summer 2000 at the
Ecological Society of America meetings entitled "Integrating
disciplines to understand and address problems in invasive species biology"
where speakers discussed specific examples
linking basic research on invasives and practical applications. In Summer
2001, the Collaboratory helped sponsor a symposium on "The Population
Biology of Invasive Species" at the Society for Conservation Biology
meetings in Hilo, Hawaii. In related work in the lab, graduate student
Jessica Poulin is investigating the role of
keystone alien species in native California habitats.
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