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.

Self-fertilization in mosses: a comparison of heterozygote deficiency between species with combined versus separate sexes

“…(see McCauley et al, 1985;Holsinger, 1987). As intragametophytic selfing results in equilibrium proportions in only one generation (McCauley et al, 1985), the assumption of equilibrium conditions for Eq.…”

“…no selection, genetic drift or microspatial population structuring), Wright's fixation index (F IS ) is equal to the inbreeding coefficient (F e ) and thus can be used to estimate an amalgam of both intergametophytic and intragametophytic selfing in haploid-dominant species with combined sexes and intergametophytic selfing in haploid-dominant species with separate sexes. While many studies have used F IS as an estimate of selfing in homosporous ferns (by assuming that intergametophytic selfing is not present; for example McCauley et al, 1985;Holsinger, 1987), in populations with significant levels of heterozygosity in two unlinked loci, Ritland's (1990) maximum likelihood method can be used to estimate both types of selfing. Low levels of heterozygosity are characteristic of many populations of mosses (Shaw, 2000), and therefore this method has only limited application.…”

“…Low levels of heterozygosity are characteristic of many populations of mosses (Shaw, 2000), and therefore this method has only limited application. While some data exist on levels of average genetic variation in ferns and mosses (McCauley et al, 1985;Shaw, 1991;Shaw, 2000) and on levels of intragametophytic selfing in ferns (McCauley et al, 1985;Holsinger, 1987;Ritland et al, 1990;Soltis and Soltis, 1992), there is a paucity of data examining how variation in breeding system influences deviations from expected levels of heterozygosity or other measures of self-fertilization rates at the diploid stage of haploid-dominant species (see Wyatt and Anderson, 1984;Wyatt, 1994;Shaw, 2000). In particular, it is important to compare selfing rates between populations with combined and separate sexes in haploid-dominant species, as individuals with combined sexes can experience both inter-and intragametophytic selfing, whereas individuals with only one sex function can only engage in intergametophytic selfing (for review see Wyatt and Anderson, 1984).…”

Reappraising the theme of breeding systems inEchinococcus: is outcrossing a rare phenomenon?

“…In farm P20, F equals 0·26. So if F is interpreted as the proportion of selfed individuals (McCauley et al 1985), that means the parasite on that farm outcrosses 74% of the time.…”

A two-locus model for the joint estimation of intergametophytic and intragametophytic selfing rates

“…Despite this potential selective disadvantage of intragametophytic selfing, electrophoretic studies have indicated high levels of such selfing in Botrychium (McCauley, Whittier and Reilly, 1985; D. Soltis and P. Soltis, 1987a; and Asplenium (Werth, Guttman and Eshbaugh, 1985), and moderate levels in Dryopteris expansa (D. Soltis and P. Soltis, 1987b). Outbreeding seems to occur in most fern species that have been examined (D. Soltis and P. Soltis, 1987a;, as well as lycopod species (P. Soltis and D. Soltis, 1988b) and Equisetum arvense (D. .…”