Ferns on Oceanic Islands - From Dispersal to Long Lasting Diversity
Windham, Michael D. , Yatskievych, George .
The roles of polyploidy and apomixis in the dispersal of ferns to oceanic islands.
Polyploidy (the multiplication of chromosome sets within a nucleus) and apomixis (the production of embryos without fertilization) are closely linked phenomena encountered throughout the tree of life. These processes are especially prevalent in ferns, where approximately 50% of named species are polyploid (or include polyploid cytotypes) and about 10% are obligate apomicts. The roles of polyploidy and apomixis in facilitating the propagation of hybrid lineages is well known; their effects on geographic distribution are more speculative. Ferns are thought to have a very high potential for long-distance dispersal due to the confluence of two factors: 1) most have very small spores (averaging 50 microns) easily transported by the wind, and 2) most have the potential to produce bisexual gametophytes that could, through intra-gametophytic selfing, give rise to new sporophytes far removed from the source population. However, this potential is rarely realized. Rates of species endemism in ferns are only slightly lower than those of seed plants. This disconnect between theory and reality may be explained by recent studies documenting that many ferns are outcrossers and must have compatible gametophytic mates in close proximity to successfully reproduce. This breeding system, which is primarily associated with diploids, puts severe limits on long distance dispersal. Polyploids, on the other hand, usually are more tolerant of selfing, and apomicts dispense with fertilization altogether. In both cases, new populations are more easily established by a single spore, facilitating species migration. Oceanic islands, located far from large land masses and never connected to them, provide a natural laboratory for studying long-distance dispersal. Using the ferns of Hawai'i and other oceanic islands as our primary data set, we will explore the effects of polyploidy and apomixis on species migration.
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1 - Duke University, Department of Biology, Durham, NC, 27708, USA
2 - Missouri Botanical Garden, P.O. Box 299, St. Louis, Missouri, 63166, USA
Presentation Type: Symposium or Colloquium Presentation
Location: Lake Michigan/Hilton
Date: Tuesday, July 10th, 2007
Time: 11:30 AM