Low allozyme variability in the critically endangered borderea Chouardii and in its congener Borderea pyrenaica (Dioscoreaceae), two paleoendemic relicts from the central pyrenees

Allozyme analyses were conducted on the two species of the Pyrenean-endemic genus Borderea (Dioscoreaceae) in order to investigate levels and distribution of genetic diversity both within and among populations of the two taxa and between them. The aim of this survey was to apply these genetic results to the taxonomy and conservation of Borderea. Eighteen enzyme systems were surveyed on the only known population of Borderea chouardii and on six populations of Borderea pyrenaica, a taxon confined to a narrow geographic area in the Central Pyrenees. Very low rates of genetic diversity were found both within and among populations. Only eight out of 21 studied loci were polymorphic regarding both species. The highest genetic distances were those between populations of B. chouardii and B. pyrenaica, a finding that supports the morphological distinctness of the two species. However, the low genetic distance values point toward a recent divergence of the two taxa. Fixed heterozygous profiles found in all of the studied individuals for the phosphoglucose isomerase-2 locus and in all the individuals of B. pyrenaica for the isocitrate dehydrogenase locus may be the result of independent gene-duplication events at these two loci or may indicate a hybrid origin of these relictual Dioscoreaceae. The genetic impoverishment of the present populations and their apparent lack of genetic structure, as revealed by the allozyme data, indicate the occurrence of severe genetic bottlenecks in the past. Our allozyme results are used to address conservation strategies for the critically endangered B. chouardii.