Plant Evolution in Robinson Crusoe Islands

This proposal seeks support for evolutionary studies on the endemic plants of the Robinson Crusoe (Juan Fernandez) Islands, a Chilean national park. These islands are located 680 kms west into the Pacific Ocean off the coast of Chile at 33 S latitude. There are 104 endemic flowering plants in two main islands, Masatierra and Masafuera, each c. 50 sq. km. Radiometric dates show the former to be c. 4 million years old and the latter 1-2 million. The geographic positioning of the islands, the small numbers of species occurring there, plus the high level of specific endemism, make them an outstanding model for addressing issues of plant evolution. The classical mode of evolution in oceanic islands is through adaptive (cladogenetic) radiation. Dramatic examples are well known, such as the Hawaiian silverswords. Less appreciated, however, is anagenetic speciation, whereby an immigrant establishes in a new island and slowly changes through time, eventually yielding a new species. This mode of evolution has occurred in approximately 25% of all oceanic island endemic species. From preliminary data, the levels of genetic variation within and among populations in species deriving from these two processes appear different, but direct tests need to be completed. Available data suggest that anagenetically derived species harbor much more genetic variation within populations than those that have originated via adaptive radiation. We have selected 19 endemic species in the genera Drimys, Dysopsis, Erigeron, Gunnera, Myrceugenia, Rhaphithamnus, and Robinsonia, for populational sampling and analysis of genetic variation within and among populations. These have been chosen for their origins via adaptive radiation (cladogenesis) or simple geographic speciation (anagenesis), and for their population sizes and ease of sampling. Amplified Fragment Length Polymorphism (AFLP), cpDNA haplotypes, nuclear microsatellites, and genome size measuremente, will be used to assess patterns of genetic variation. Observed genetic patterns will be correlated with age of islands, geographic distances, reproductive systems, and environmental variables as reflected by different vegetational types. The collaborative research team, which includes Austrian, American and Chilean investigators, has more than 25 years of experience in this archipelago, involving ten previous expeditions, with the publication of more than 60 papers on the evolution of its flora. This provides an excellent base from which to address the proposed research. This project will be the first detailed molecular analysis of genetic variation within a number of plant populations of different species in the same oceanic archipelago. This project will generate data that will bear on the fundamental question of genetic variation and divergence during speciation of plants in oceanic archipelagos. It will also produce the first modern vegetation map of Masafuera. The project also has high conservation implications.

This research project has focused on understanding the genetic changes involved with the origin of plant species in the Robinson Crusoe Islands, which are one of Chiles national parks. Approximately 100 flowering plant species have originated from progenitors that arrived to the islands by long-distance dispersal. After arrival and establishment of viable new populations, changes in the genetic composition of these immigrant populations have resulted in new species by two principal modes. One well-known mechanism is via adaptive radiation, whereby dispersal of individuals from the founding population into diverse ecological niches in the islands has driven evolutionary modification and resulted in new species. The other mechanism is where the successful population does not disperse to new ecological zones but instead simply increases in size and accumulates more genetic variation through mutation and recombination over many generations. We have hypothesized that the range of genetic variation within each new species derived via adaptive radiation should be less than in cases involving simple transformational (anagenetic) speciation. We have tested this hypothesis by using DNA markers to reveal precisely the genetic profiles within each of 14 species found only in the Robinson Crusoe Islands. Nine of these species reflect a pattern of adaptive radiation and five of them transformational speciation. The results from analysis of more than 6000 individual plants in over 350 populations are consistent with the initial hypotheses. This is the most detailed study done on the genetic divergence of endemic plants in an oceanic archipelago. These results also reveal patterns of genetic variation over the island landscape, which have direct relationship to conservation management of these island species. Results of these studies are being communicated to the administration of the Robinson Crusoe Islands national park.Studies on the vegetation of the most remote island, Masafuera, has resulted in a modern map of the vegetation of this island, the first ever produced. This will be of great value for the National Park service of the islands, especially for conservation and educational purposes. Furthermore, because we produced previously the first modern vegetation map for the other major island, Masatierra, we now have an opportunity to compare and contrast the structure of the vegetational communities between the two islands that are of different geological ages (4 vs. 1-2 million years old). In addition, the combination of new ecological data plus detailed genetic analyses provide a more precise environmental context for interpreting the different modes of speciation.