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

Background: The patterns of inbreeding coefficients (F_IS) 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; F_IS; F_ST; 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 F_IS 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). F_ST 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. F_IS 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.