Fly-pollinated Pleurothallis (Orchidaceae) species have high genetic variability: Evidence from isozyme markers

We conducted an isozyme study in 22 populations of five Pleurothallis (Orch idaceae) species (12 loci in nine enzymatic systems). The genetic variabili ty in all populations is surprisingly high (P = 58-83%, A = 2.1-3.8, H-e = 0.25-0.43) in spite of the fact that the five species are pollinated by sma ll flies whose behavior enables self-pollination. We suggest that self-inco mpatibility, inbreeding depression, and mechanical barriers that prevent se lf-pollination in these species are responsible for the maintainance of the high genetic variability. These traits are uncommon in Orchidaceae, but ha ve been observed in these and some other species pollinated by flies or oth er pollinators with behavior that facilitates self-pollination The genetic similarity among conspecific populations is also high for species with very shea-range flying pollinators. Only one population of P. teres presented v alues of genetic similarity lower than usually observed in allopatric consp ecific populations. Morphology, however, does not support its segregation a s a new taxon. Ail species can be recognized by their enzymatic patterns, a nd the results agree with recently proposed taxonomic realignments. Convers ely, the supposed affinities among these species based on floral morphology are not supported, and we hypothesize that it may be due to convergence in species with similar pollinators.