Origin of the Appalachian Gametophyte

Pinson, Jerald

"Vittaria appalachiana is a fern that grows on porous rock outcrops near streams throughout the Appalachian Mountains. This particular species, however, spends its entire lifecycle in the haploid (gametophyte) stage; it is the only fern to completely lack a known sporophyte population anywhere in the world. This species also has other confounding genetic traits as well. This species is a polyploid, with a chromosome count (n=120) twice what might be expected in relation to its closest relative (Gastony, 1977). The lack of a sporophyte in Vittaria appalachiana, along with its genetic disposition, suggests that it may have originated via an ancient hybridization event, with the subsequent extinction of its sporophyte generation. However, much remains unknown about the evolutionary history of this species. The proposed research aims to better elucidate the origin of Vittaria appalachiana and centers on three primary objectives: (1) to determine whether V. appalachiana is of hybrid origin (and if so, to determine the identity of the progenitors), or is representative of a divergent speciation event; (2) determine the mode of dispersal for V. appalachiana inferred from intraspecific genetic variation between populations; (3) attempt to estimate the date of hybridization or divergence for V. appalachiana. Hia results indicate that a hybrid origin is unlikely and that V. appalachiana was instead derived from within the V. graminifolia lineage."