Genetic diversity and structure in fragmented populations of the tropical orchid Myrmecophila christinae var christinae

In recent years the coastal dune vegetation of the state of Yucatan, Mexico has become highly fragmented due to clearing for development. We evaluated patterns of genetic differentiation and genetic variability among orchid populations (Myrmecophila christinae var christinae) in eight habitat fragments along a west-to-east disturbance gradient in which sites located on the western end began experiencing fragmentation earlier than those in the east. Leaf samples from adult individuals and juvenile plants were collected from all eight populations, and analyzed using starch-gel electrophoresis in a lithium buffer system. Per population estimates of genetic diversity, proportion of polymorphic loci at 95 percent, mean number of alleles per locus, allelic richness, and population structure were calculated, as well as estimate comparisons between generations. Genetic diversity at the loci analyzed did not show significant differences among the eight populations. Based on the results, the model of isolation by distance does not fit the M. christinae populations under study; in some cases, populations close to one another apparently experienced very little genetic exchange. Thus, we propose that so far, fragmentation has not led to significant genetic differences between populations subject to different historical backgrounds of disturbance (i.e., time since onset of disturbance), as well as between generations within each of the M. christinae study populations. Nevertheless, the genetic characteristics of some remnant populations might change over time due to a future decrease in the opportunities for genetic exchange with other populations.