Is Allotetraploid Evolution in Terns a Species Pump? Gary Greer, Biology Department, Grand Valley State University Ferns including Psilotopsida, Equisetopsida, Marratiopsida, and Polypodiopsida are currently the second most species rich plant clade after angiosperms and are characterized by large diploid base numbers and hybrid swarms. Diploid hybrids are typically sterile; however, sterility can be escaped through formation of unreduced spores, which is likely due to the high fecundity and longevity of most fern sporophytes. Unreduced allodiploid spores develop into gametophytes capable of producing allotetraploid sporophytes through suiting or sib meting. Silencing of redundancy in the allotetraploid genome results in a diploid genome; i.e., neodiploid species with large base numbers reflecting ancient polyploidy status. Allopolyploid evolution coupled with diploidization may also facilitate the formation of new species capable of utilizing unique niches via plasticity and subsequent niche specialization. My first step in investigating this possibility was to analyze the relationship between base number and species richness at various levels within the fern clade. A significant but weak relationship was revealed within select clades and taxonomic levels supporting the hypothesis that allopolyploid evolution may be contribute to the persistence and species richness of ferns.
