Chloroplast DNA polymorphisms in Tsuga canadensis and Tsuga caroliniana

We have surveyed chloroplast DNA restriction fragment length polymorphisms in natural populations across the range of Tsuga canadensis (L.) Carr. and in one natural population of Tsuga caroliniana Engelm. The survey included 179 T. canadensis individuals from seven main-range populations, three glaciated outlier populations, and five unglaciated outlier populations, as well as 11 individuals of T. caroliniana. Molecular hybridizations with approximately 13 kilobase pairs from the Pinus contorta var. latifolia Engelm. chloroplast genome detected five PstI variants and four XhoI variants in T. canadensis, with as many as three PstI and four XhoI variants per population. Unbiased variant diversity estimates were as high as 0.73 within single populations. Frequency differentiation of these variants among the T. canadensis populations was modest at best, even between main-range populations and unglaciated outliers. The low level of population subdivision may be due to chloroplast gene flow through pollen and(or) generation of convergent variants by a mutation hot spot. The sampled T. caroliniana population's XhoI variant frequencies differed substantially from those of its neighboring T. canadensis population. This difference is consistent with the lack of literature evidence for hybridization between the two species. The chloroplast variants reported here may be useful for microevolutionary investigations.