Genetic consequences of fragmentation on populations of the terrestrial orchid Cymbidium goeringii

Population genetics theory predicts that fragmented plant populations do exhibit less genetic diversity, greater genetic divergence, and higher rates of inbreeding than well-preserved, continuous populations. We investigated the effects of habitat fragmentation on levels and distribution of genetic diversity and inbreeding in the terrestrial orchid Cymbidium goeringii on three islands off the south coast of South Korea. We selected two case studies, each containing 10 fragmented and 10 continuous (i.e. undisturbed) populations (40 populations and 1493 individuals in total); for both case studies, fragmentation has been recorded for almost 200 years. Using nine polymorphic allozyme loci, we compared genetic diversity and structure between fragmented and continuous populations for each of two case studies. We found that continuous populations harboured significantly greater allelic richness (AR) than fragmented ones. We also found that fragmented populations exhibited two- to threefold higher degree of genetic differentiation (FST) than continuous ones. We did not found, however, significant differences for expected heterozygosity (He) and fixation index (FIS). Fragmentation effects are noticeable in C. goeringii as AR was significantly reduced in fragmented populations. The lack of significant differences for He would be attributable either to insufficient number of generations elapsed from the beginning of fragmentation, to the high density of individuals in undisturbed populations, or to both. The loss of allelic diversity detected in disturbed populations of C. goeringii is still small, and could be recovered if the current moderate levels of gene flow are maintained and no further fragmentation is occurring.