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Variability of allozymes (1170 individuals, 47 populations) and chloroplast DNA (692 individuals, 29 populations) was examined in native European and introduced North American populations of Epipactis helleborine (Orchidaceae). At the species level, the percentage of allozyme loci that were polymorphic (P99) was 67%, with a mean of 2.11 alleles (A) per locus, and an expected heterozygosity (Hexp) of 0.294. At the population level, mean P99 5 56%, mean A 5 1.81, and mean Hexp 5 0.231. Although field observations suggest that self-pollination occurs frequently, populations had a genetic structure consistent with Hardy-Weinberg expectations and random mating (mean FIS 5 0.002). There was significant deviation from panmixia associated with population differentiation (mean FST 5 0.206). The distribution of two chloroplast haplotypes showed that 15 of the 29 populations were polymorphic. Using both nuclear and organelle FST estimates, a pollen to seed flow ratio of 1.43 : 1 was calculated. This is very low compared with published estimates for other plant groups, consistent with the high dispersability of orchid seeds. Finally, there was no evidence for a genetic bottleneck associated with the introduction of E. helleborine to North America. |
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