ISOZYME VARIATION IN OAKS OF THE APOSTLE ISLANDS IN WISCONSIN - GENETIC-STRUCTURE AND LEVELS OF INBREEDING IN QUERCUS-RUBRA AND Q-ELLIPSOIDALIS (FAGACEAE)

Isozyme variability was examined in populations representing the red o ak complex (Quercus subg. Erythrobalanus) on an island archipelago and adjoining peninsula in Lake Superior, near Bayfield, Wisconsin. A con comitant study of morphometric variation described in the companion ma nuscript, revealed a continuum in leaf morphology extending from an in terior mainland site to the outermost island. The existence of this cl inal variation presented an ideal opportunity to examine the genetic s tructure of a hybrid population along with the putative progenitor spe cies. Dormant leaf bud samples were collected from specimens of Quercu s rubra L., Q. ellipsoidalis Hill, and their putative hybrids from thr ee islands and two locations on the peninsula. Acorns were collected f rom some of these same trees from one peninsula location and two islan ds. Twelve putative enzyme loci from six enzyme systems were analyzed. Allele frequency data indicated little differentiation between popula tions. Mean F(ST) values for the adult trees and acorns were 0.042 and 0.020. Genetic identities according to Nei ranged from 0.958 to 0.999 . Despite these high levels of genetic similarity, the populations app eared to be highly inbred as indicated by positive mean F(IT) values o f 0. 183 and 0.373 for the adult trees and acorns. Estimates of migrat ion rate per generation (Nm) for the adult trees was 5.70, a value tha t is low when compared to estimates for other plant species with simil ar life history characteristics.