Am. Arft et Ta. Ranker, ALLOPOLYPLOID ORIGIN AND POPULATION-GENETICS OF THE RARE ORCHID SPIRANTHES DILUVIALIS, American journal of botany, 85(1), 1998, pp. 110-122
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.