Contrasting patterns of spatial genetic differentiation in two east asian five-needle pine species, Pinus koraiensis and P. armandii

Abstract

Two species of East Asian five-needle pines of the section Strobus, Korean pine, Pinus koraiensis Sieb. et Zucc. and Armand's pine, Pinus armandii Franch are traditionally placed in two different subsections, Cembrae and Strobi, respectively. However, data on similarity of these pines in needle anatomy and pollen structure are reported. By means of starch gel electrophoresis we studied allozyme variation within populations of these species and between the two species. Among 30 studied loci we selected 17 polymorphic loci with reliable interpretation of allele correspondence between species. Allozyme patterns were similar in both species with respect to number of loci and predominant alleles at most loci. Intra-specific differentiation among 12 populations of Pinus koraiensis from Russia, Northeast China and South Korea was low, FST (proportion of among population variation in total variation) was as low as 0.019, DN (Nei's genetic distance) varied between 0.001 and 0.006. This genetic uniformity can be explained by a common gene pool of this species within virtually continuous range under similar ecological conditions. Common vectors of selection, natural gene flow through pollen and seed dispersal as well as mixing of genetic material between regions by humans (at least in Russian forestry practice) are putative factors responsible for low differentiation in Korean stone pine. We estimated the same parameters in Pinus armandii from continental China (Guizhou, Shaanxi, Shenyan) where its range is highly fragmented, and found differentiation in this species to be much more pronounced (FST = 0.067, DN = 0.011-0.029). By adding a sample from Taiwan both FST (0.338) and DN (up to 0.232) were substantially higher indicating high level of differences between continental and Taiwanese P. armandii, putatively due to longer isolation time. Maximal contribution was from loci Adh-1, Got-3, Mdh-1, 6-Pgd-3, Pgm-2 and Skdh-2. Differences were mainly caused by allelic frequencies but not by presence/absence of particular alleles, therefore observed allozyme patterns are not evidence for full species' status of Taiwan variety. In the two species, P. koraiensis and P. armandii, electrophoresis showed the same number of activity zones. In a combined set of P. koraiensis and P. armandii samples, the level of interspecific differences was high (FST = 0.477, DN = 0.407÷0.457). Species had no common alleles or very little overlapping in allelic profiles at loci Adh-1, Got-2, and Pgm-1. Out of 61 alleles 35 were shared between species and 26 were found in only one of them. Cluster (UPGMA) and multivariate (PCA) analyses of allozyme variation showed good differentiation within P. armandii, and poor differentiation within P. koraiensis.