Submitted to: American Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2003
Publication Date: 12/31/2003
Citation: Lott, M., Volin, J., Pemberton, R.W., Austin, D. 2003. The reproductive biology of lygodium microphyllum and l. japonicum (schizaeceae): implications for invasive potential.. American Journal of Botany. 90: 204-207 Interpretive Summary: Japanese climbing fern (Lygodium japonicum) and Old World climbing fern (Lygodium microphyllum) are important invasive plants of natural areas in the southern US and Florida. Both ferns are spreading rapidly by their wind borne spore. Successful long distance dispersal in ferns is thought to rely on the ability of the sexual stage of the fern, the small thin liverwort-like form (called a gametophyte that grows from the spore), to self fertilize. After fertilization the gametophyte grows the familiar large fern body (the sporophyte or spore producing stage) The possibility of self fertilization was evaluated by growing the gametophytes of both ferns in isolation, in pairs and in groups. Both ferns were able to self fertilize. Japanese climbing fern gametophytes rapidly grow both female and male organs and then self fertilize via the swimming sperm produced by the male organs. Old World climbing fern gametophytes, however, first grow female organs and then outcross with nearby bisexual gametophytes. If this does not occur, the female phase gametophytes hormonally induce nearby presexual gametophytes to grow male organs first, enabling them to be then fertilized by the swimming sperm produced by these male gametophytes. If this cross fertilization does not occur, the female phase gametophytes of this fern grow male organs and self fertilize. The ability of the ferns to self fertilize means that only one spore is needed to start a new infestation, which is thought to greatly enhance their ability to spread and invade new areas. The sporophyte stages of these fern grows rapidly which is likely to promote higher survival in the wet-dry seasonal climate of Florida.
Technical Abstract: The effect of culture system and population source on sexual expression and sporophyte production was examined for two invasive fern species in Florida, Lygodium microphyllum and L. japonicum (Schizaeaceae). Both species are currently spreading through Florida. Long-distance dispersal of ferns is thought to rely on successful intragametophytic selfing. Given the rate of spread observed in both Lygodium species, we hypothesized that both species are capable of intragametophytic selfing. To test this hypothesis, gametophytes of both species were grown in vitro as isolates, pairs, and groups. Both species were capable of intragametophytic selfing; 78% of L. microphyllum isolates produced sporophytes and over 90% of the L. japonicum isolates produced sporophytes. Lygodium microphyllum also displayed the ability to reproduce via intergametophytic crossing, facilitated by an antheridiogen pheromone. Sporophyte production was rapid across mating systems for both species, an advantage in Florida's wet and dry seasonal cycles. The high intragametophytic selfing rate achieved by both species has likely facilitated their ability to colonize and spread through Florida. The mixed mating system observed in L. microphyllum appears to give this species the ability to invade distant habitats and then adapt to local conditions.