Genetic load and long-distance dispersal in Asplenium platyneuron

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Abstract
Solitary plants of Asplenium platyneuron occur disjunctively on recently produced coal spoils in southern Iowa. They are assumed to have been produced by self-fertilization of isolated gametophytes and therefore highly homozygous. Cultures of isolated and paired gametophytes originating from these solitary sporophytes produced second-generation sporophytes with 89 and 93% success, respectively, indicating a low genetic load as expected. The failure of gametophytes from coal-spoil plants to produce sporophytes with even greater success may result from homoeologous chromosome pairing and recombination at meiosis which allows production of variable spores and expression of genetic load from plants produced by self-fertilization of single gametophytes. Cultures of isolated and paired gametophytes originating from sporophytes in populations central to the species' range produced second-generation sporophytes with 83 and 90% success, respectively, indicating a significantly greater genetic load in populations but still a relatively low genetic load for the species. Through low genetic load, regularity of sporophyte production from isolated gametophytes, and ability of such plants to release variability through homoeologous chromosome pairing, Asplenium platyneuron is remarkably adapted for, and successful in, colonizing distant habitats through long-range spore dispersal.