Genetic diversity in mainland and island populations of the endangered Pancratium maritimum L. (Amaryllidaceae) in Tunisia

Tunisian Pancratium maritimum L. populations are at present endangered and represented by scattered individuals as a result of coastal habitat destruction caused by urbanization and overharvesting for its significant ornamental interest. Nineteen populations growing in mainland and island habitats were sampled for allozyme diversity to assess their genetic diversity and structuration using seven isozymes revealed by starch gel electrophoresis. The species exhibited relatively high levels of genetic diversity (the mean Ap = 1.37, P = 37.4%, and He = 0.100), indicates a preferentially outcrossing mating system.Except in the well-known touristic island Djerba, the genetic diversity in island P. maritimum populations is higher than that in mainland ones. This observation might result from the high diversity of genets at the starting population, the migration of seeds from mainland to islands and the coastal habitat degradation in mainland.Nei's genetic distances (D) between populations were low; noticing a high level of similarity among them and it would give evidence of inbreeding. The UPGMA cluster analysis of genetic distance values revealed that island populations were strictly clustered to mainland ones. The model of population grouping might be related to the dispersal of seeds by seawater and wind.The low genetic divergence among populations and their high structuring indicate their recent isolation as a result of coastal habitat destruction by anthropic pressures. The continuous eradication of P. maritimum populations reduced their size and contributed to enhancing their differentiation level unless in situ and ex situ conservation measures are adopted very fast.