Detection of low genetic variation in a critically endangered Chinese pine, Pinus squamata, using RAPD and ISSR markers.

With only 32 individuals in the northeastern corner of Yunnan Province, China, Pinus squamata is one of the most endangered conifers in the world. Using two classes of molecular markers, RAPD and ISSR, its very low genetic variation was revealed. Shannon's index of phenotypic diversity (I) was 0.030, the mean effective number of alleles per locus (Ae) was 1.032, the percentage of polymorphic loci (P) was 6.45, and the expected heterozygosity (He) was 0.019 at the species level based on RAPD markers. The results of ISSR were consistent with those detected by RAPD but somewhat higher (I = 0.048, Ae = 1.042, P = 12.3, He = 0.029). The genetic variation of the subpopulation on the southwest-facing slope was much higher than that of the subpopulation on the northeast-facing slope, which may be attributed to the more diverse environment on the southwest-facing slope. The genetic differentiation between the two subpopulations was very low. The between-subpopulation variabilities, phiST, calculated from RAPD and ISSR data were 0.011 and 0.024. Because of the lack of fossil records and geological historical data, it was difficult to explain the extremely low genetic diversity of the species. We postulate that this ancient pine might have experienced strong bottlenecks during its long evolutionary history, which caused the loss of genetic variation. Genetic drift and inbreeding in post-bottlenecked small populations may be the major forces that contribute to low genetic diversity. Human activities such as logging may have accelerated the loss of genetic diversity in P. squamata.