ALLOPOLYPLOID ORIGIN AND POPULATION-GENETICS OF THE RARE ORCHID SPIRANTHES DILUVIALIS

The process of becoming and the attributes of being polyploid play a m ajor role in the development and maintenance of genetic variation in a llopolyploid species. A genetic survey employing protein electrophores is on 12 populations of S. diluvialis, as well as on populations of ei ght congeneric species, was conducted to assess the putative allopolyp loid origin of S. diluvialis and to determine the genetic variability within and among populations. Genetic identity values indicated S. dil uvialis was more similar to S. magnicamporum (0.619) and S. romanzoffi ana (0.727) than to any of the other congeneric species assayed. Simil ar to most allopolyploids, S. diluvialis showed high levels of fixed, or nearly fixed, heterozygosity and a high percentage of polymorphic l oci (57.1-71.4%). The mean number of alleles per polymorphic locus in populations of S. diluvialis (2.6-3.3), however, was similar to mean v alues for both animal-pollinated, outcrossing, diploid species, and ge ographically restricted, diploid species (2.6 and 2.5, respectively). Genetic divergence among populations (mean F-st = 0.083) was low, lead ing to relatively high estimates of interpopulational gene flow (mean Nm = 5.41). Thus, each population harbors most of the genetic variabil ity found within the species. The genetic variation observed within S. diluvialis supports the occurrence of at least two separate hybridiza tion events giving rise to S. diluvialis.