Concordant Patterns of Population Genetic Structure in Food-Deceptive Dactylorhiza Orchids

Background: The patterns of inbreeding coefficients (FIS) and fine spatial genetic structure (FSGS) were evaluated regarding the mating system and inbreeding depression of food-deceptive orchids, Dactylorhiza majalis, Dactylorhiza incarnata var. incarnata, and Dactylorhiza fuchsii, from NE Poland. Methods: We used 455 individuals, representing nine populations of three taxa and AFLPs, to estimate percent polymorphic loci and Nei’s gene diversity, which are calculated using the Bayesian method; FIS; FST; FSGS with the pairwise kinship coefficient (Fij); and AMOVA in populations. Results: We detected a relatively high proportion of polymorphic fragments (40.4–68.4%) and Nei’s gene diversity indices (0.140–0.234). The overall FIS was relatively low to moderate (0.071–0.312). The average Fij for the populations of three Dactylorhiza showed significantly positive values, which were observed between plants at distances of 1–10 m (20 m). FST was significant in each Dactylorhiza taxon, ranging from the lowest values in D. fuchsii and D. majalis (0.080–0.086, p < 0.05) to a higher value (0.163, p < 0.05) in D. incarnata var. incarnata. Molecular variance was the highest within populations (76.5–86.6%; p < 0.001). Conclusions: We observed concordant genetic diversity patterns in three food-deceptive, allogamous, pollinator-dependent, and self-compatible Dactylorhiza. FIS is often substantially higher than Fij with respect to the first class of FSGSs, suggesting that selfing (meaning of geitonogamy) is at least responsible for homozygosity. A strong FSGS may have evolutionary consequences in Dactylorhiza, and combined with low inbreeding depression, it may impact the establishment of inbred lines of D. majalis and D. incarnata var. incarnata.