Evaluating Genetic Diversity for the Conservation of the Threatened Galapagos Endemic Calandrinia galapagosa (Portulacaceae)

Calandrinia galapagosa (Portulacaceae) is a threatened plant endemic to San Cristobal Island, Galapagos. The species is threatened by goat herbivory: less than 1300 individuals remain in nine populations, three of which have been fenced for protection. It is not known whether these three populations are genetically representative of the species at large or whether the three distinct color morphs exhibited by the species represent different taxonomic units. We measured the frequency of 113 polymorphic amplified fragment length polymorphism markers in 189 specimens representing three different phenotypes from all nine populations to relate the genetic structure of the species to both its geological history and morphological variation. The analysis revealed high diversity within populations and low, but significant, differentiation between populations. In addition, no genetic diversification was observed across color morphs. We conclude that (1) regular gene flow has historically occurred between populations, and (2) individual color morphs are not separate taxa. We identify another population that should be fenced to ensure maximal protection of genetic variation. Our research serves as a case study of using population molecular genetics for optimizing protection strategies for rare plants in tropical archipelagoes affected by introduced herbivores.