Patterns and Levels of Genetic Variation in Great Basin Bristlecone Pine, Pinus longaeva
Patterns and levels of genetic variation were studied in five bristlecone pine (Pinus longaeva) populations in the eastern Great Basin. Fourteen enzyme loci were examined using horizontal starch gel electrophoresis. Low but significant levels of genetic variation were observed among populations. No patterns of decreasing genetic identity were observed with an increase in geographic separation. In contrast, levels of genetic variation within populations were high. All populations were polymorphic for the same 11 loci. Levels of heterozygosity were effectively the same in all populations with a mean heterozygosity of 0.327 Genetic identity between altitudinal zones within populations was effectively the same as that between populations. Analyses were also done to determine if there were deviations in expected genotype frequencies. All but two of the loci deviated significantly from expectations in at least one population. A cp-4 had consistent excesses of heterozygotes while Gdh-3, Lap-8 and Got-5 have consistent deficiences. All other polymorphic loci deviated from the expected in both directions. The low interpopulation variation and the high intrapopulation variation, along with paleoecological data, argue for the continuity of bristlecone pine throughout much of the Great Basin during the last full glacial. The maintenance of high levels of variation from that time until the present are a result of several factors which would appear to include: (1) high outcrossing rates; (2) maintenance of large population sizes; (3) production of large numbers of seeds; (4) microhabitat adaptation in a spatially and temporally heterogeneous environment.
Hiebert, R.D., Hamrick, J.L. 1983. Patterns and levels of genetic variation in Great Basin Bristlecone Pine, Pinus longaeva. Evol. 37(2):302-310.