Isozyme Variation in North American Menziesia (Ericaceae)

Abstract

Starch gel electrophoresis was used to examine genetic variation in the two subspecies of Menziesia ferruginea from western North America and M. pilosa from the Appalachians. Genetic variation within and among populations of both species was less than expected for widespread long-lived woody perennials but was comparable to levels reported for outcrossed animal-pollinated species and species with gravity dispersed seeds. The total heterozygosity, mean HT = 0.146, is lower than observed in most plant species. The partitioning of genetic diversity was largely within rather than among populations, with GST ranging from 0.147 to 0.300. Menziesia ferruginea exhibited geo- graphic variation, with differences in allozyme frequencies in Gpi-2, 6Pgd-1, 6Pgd-2, and Idh-1 being noted between eastern and western populations of the species. Reduced genetic variation was observed in populations at both northern and southern distributional extremes, especially in M. ferruginea, indicative of bottleneck events. These patterns may be related to geological and glacial history events. The genetic identity between the western subspecies is high (I = 0.98), indicating that they have been in contact as recently as 60,000-80,000 years before present. Despite their widespread disjunction, M. pilosa and M. ferruginea s.l. are remarkably similar (I = 0.92), pointing to contact between them during the Pleistocene, some 400,000 to 800,000 years before present, much later than previously thought. Menziesia Smith is a genus of erect or spread- ing deciduous shrubs in tribe Rhodoreae D. Don of the Ericaceae (Stevens 1971). This distinct, perhaps relatively primitive member of the Rhodoreae (Kron and Judd 1990), is disjunc- tively distributed, with eight species in Japan