Range-wide patterns of allozyme variation in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco)

Graduation date: 1986One hundred and four seed sources from throughout the range of Douglas-fir (Pseudotecia menzieaii (Plirb.) Franco)\ud were analysed at 20 enzyme loci to determine patterns of genetic variation and to examine intraspecific phylogeny. On average the seed sources were polymorphic at 37 percent\ud of the loci (range 5.0-65.0), with mean expected heterozygosity equal to .141 (range .021-.243). Of the total genie diversity (H1 = .182) observed in the species. about 75 percent resided within seed sources; 12 percent was due to dfferences among the two recognized varieties. coastal (var. menziesii) and interior (var. plauca,) Douglas-fir; and, 13 percent was distributed among seed sources within varieties respectively. Cluster analysis based on\ud Nei's unbiased genetic distances resulted in two groups of seed sources corresponding to the two varieties with the interior variety additionally separated into northern and\ud southern subgroups near 440 latitude. A major transition zone between the two varieties was found in central Oregon but not in other regions as revealed in earlier\ud investigations. On averages seed sources within the coastal variety and northern interior subgroup had higher levels of\ud expected heterozygosity but genetic differentiation among seed sources was small. Levels of expected heterozygosity\ud were much smaller in the southern interior subgroups but seed sources were highly differentiated. Genetic variation was clinally patterned in the interior variety but no obvious geographical patterns were found in the coastal variety. In general genetic diversity decreased towards the periphery of the species range. Range-wide patterns of variation based on allozymes were quite similar to those observed in terpene studies of Douglas-fir. A major\ud exception was that seed sources from the Sierra Nevada Mountains of California had a high affinity with the coastal variety as revealed in this study but appeared to more closely aligned to the interior variety in a terpene study. On the broad scales range-wide patterns of genetic variation in Douglas-fir agreed well with paleobotanical\ud history for Douglas-fir; divisions and migrations associated with clmatic and geologic changes were reflected in allozyme\ud patterns