Spatial Patterns of Chloroplast DNA and Cone Morphology Variation within Populations of a Pinus banksiana-Pinus contorta Sympatric Region

The spatial distributions of cone morphology and paternally inherited chloroplast DNA variants were studied at two sites in a Pinus banksiana-Pinus contorta sympatric region of natural hybridization. Variants of both polymorphisms were distributed nonrandomly at each location, with several variants arranged in conspicuous clusters. Spatial patterns were consistent with differential selection among microenvironments, recent introduction of new variants, and limited gene flow between the two species. Spatial co-occurrence of hybrid (or hybrid derivative) and parental variants indicates that hybrids (or hybrid derivatives) can be restricted in space in sympatric populations in which one of the parental genotypes is infrequent. Pooling of individually rare variants into synthetic categories before spatial autocorrelation analyses should be treated cautiously, because such pooling can lead to erroneous conclusions regarding spatial patterns of variation.