ESTIMATION OF GENE FLOW AND GENETIC NEIGHBORHOOD SIZE BY INDIRECT METHODS IN A SELFING ANNUAL, TRITICUM DICOCCOIDES

Abstract

Rates of gene flow and neighborhood area were investigated in the selfing annual, Triticum dicoccoides. The collection of seed material was made using a spatial hierarchical sampling design in which four collection sites were 5?7 m apart, four were 15?17 m apart, and four were 100?120 m apart. Between 25 and 30 plants were scored from each site (mean sample size = 28.7). Two procedures for indirect estimation of gene flow were used on gene-frequency data from 13 polymorphic loci. The estimates of Nm using Wright's (1943a, 1943b) estimation procedure were 1.265, 0.212, and 0.357, for the closest, intermediate, and most distant distance classes, respectively. The estimates of Nm using Slatkin's (1985) private-allele procedure were 4.675 (subsample ranges: 1.544?4.675), 0.110 (subsample ranges: 0.069?0.153), and 0.670 (subsample ranges: 0.129?0.256). The results indicate a general agreement between the two procedures. Both indicate a sharp decrease in gene flow beyond the first distance class (5?7 m). The large gene-flow values and the large variation within the 5?7-m distance class are taken as evidence that a genetic neighborhood for this species may cover an area defined by a 5-m radius. The results also indicate that gene flow between populations separated by only 10 or more meters may be quite limited.