A quantitative measure of introgression between lodgepole and jack pines

Analyses of electrophoretic and morphological data for 37 populations of jack and lodgepole pine and their putative hybrids reveal (i) species are discrete, taxonomic entities that can be reliably distinguished; (ii) the two data sets yield concordant results with respect to species characterization and the detection and quantification of introgressive hybridization events; (iii) multiple localized introgressive hybridization events have occurred in Alberta and possibly the Yukon as a result of historical and ecological factors such as fire, glaciation, migration, edaphic preference; and (iv) introgression has probably had a significant evolutionary impact on these species in localized regions of the zone of species sympatry. Procedures developed elsewhere for the quantification of racial admixture in human populations provide sensitive estimates of gene exchange (introgression). Anderson's classic approach to the study of introgression using hybrid indices also provides relatively accurate accounting of gene exchange between taxa.