Genetic differentiation in endemic Silene (Caryophyllaceae) on the Hawaiian Islands

Endemic Hawaiian Silene colonize new lava flows and are outcompeted as the ground ages. They illustrate the genetic processes operating in the evolution of pioneering island plants. The volcanic history of the Hawaiian Islands allows an estimation of the age of these plant populations. In this study, populations of S. struthioloides from Maui and the older part of the island of Hawaii, and S. hawaiiensis from the youngest volcanoes of the island of Hawaii were analyzed by enzyme electrophoresis. The genetic structures of these populations were placed in a geographic and geologic context. Silene is much more polymorphic on the older island, Maui. Genetic variation appears to have been lost in the colonization of the youngest island, Hawaii. Interestingly, some loci for populations on the younger volcanoes of the island of Hawaii are monomorphic for alleles not found in populations on the older part of Hawaii. Recurrent colonizations are accompanied with founder effects, and restricted gene flow among populations has led to isolation and genetic drift. This has resulted in genetic and morphological differentiâtion of Silene populations on the youngest volcanoes.