INBREEDING AND THE RATE OF SELF‐FERTILIZATION IN A GRAPE FERN, BOTRYCHIUM DISSECTUM

Abstract

Botrychium dissectum is a homosporous fern with bisexual, subterranean gametophytes. Because of these features, B. dissectum would be suspected of displaying a very high frequency of self‐fertilization. Sporophytes collected from three populations of this species were assayed for heterozygosity by determining the electrophoretic mobility patterns displayed by two polymorphic enzymes. Extreme deviations from Hardy‐Weinberg expectations were observed in each population and analyzed by means of F ‐statistics. The average inbreeding coefficient was found to be 0.951. A population genetic model is derived that demonstrates that the rate of intragametophytic self‐fertilization in homosporous ferns is equal to the inbreeding coefficient calculated from deviations from Hardy‐Weinberg expectations. It is therefore concluded that B. dissectum outcrosses about 5% of the time.