Evolution of Plants of Ullung Island

This proposal seeks support for studies on the evolution of the endemic vascular flora of Ullung Island, Korea, located 150 km E of the Korean peninsula at 37 N latitude. Confined within the 70 km 2 of Ullung Island are 28 endemic angiosperms. This island is volcanic, with no previous connections to continents, and is 1.8 million years old. Previous work on Ullung Island includes a good inventory of taxa, a survey of vegetation, an analysis of human impact, and general discussions on phytogeography. What has not been investigated is the evolution of the endemic flora with regard to specific origins and ancestors, character change during speciation, and effects of founder impact and genetic drift on variation within endemic taxa. This proposal focuses on the following endemic species: Abelia insularis (Caprifoliaceae), Acer takismense (Aceraceae),Acer okamotoanum, Dystaenia takesimana (Umbelliferae), Fagus multinervis (Fagaceae), Hepatica maxima (Ranunculaceae), Physocarpus insularis (Rosaceae), Rubus takesimensis (Rosaceae), Valeriana officianalis var. integra (Valerianaceae), Viola insularis (Violaceae) and V. takesimana. These include genera from eight different families and three different habit types. Previous work has identified continental relatives of these endemic taxa (in order of above list): Abelia coreana (Korea), Acer pseudo-sieboldianum (Korea), A. mono (Korea and Japan), Dystaenia ibukiensis (Japan), Fagus crenata (Japan), Hepatica asiatica (Korea), Physocaripus amaurensis (or also possibly P. intermedius, both Korea), Rubus crataegifolius (Korea and Japan), Valeraniella faurei (Korea and Japan) , Viola kusanoana (Korea and Japan), and V. gypoceras (Korea and Japan). We propose to (1) analyze morphological, cytological, and breeding system changes that have taken place during evolution of island species; (2) measure genetic differences between progenitor and derivative species through sequence differentiation in nuclear and chloroplast DNA; (3) determine degree of genetic diversity within and between populations in continental and island taxa using isozymes and RAPDs; and (4) summarize patterns and processes of evolution during phyletic evolution. Of special importance is that there apparently has been no cladogenetic speciation in Ullung Island: all evolution has been phyletic with gradual changes from original immigrants. Reasons for this lack of cladogenesis are unclear, but a preliminary hypothesis points to the young age of the island and lack of habitat diversity that ordinarily serve as a stimulus for evolutionary divergence. As such, Ullung Island is an ideal system in which to study the structural, reproductive, and genetic changes involved with initial evolution in an isolated oceanic island.

Oceanic islands of volcanic origin are natural laboratories for the study of plant evolution. The study of endemic island taxa has the potential of revealing patterns and processes of biological evolution with a clarity beyond that possible in continental groups. Advantages of island investigations include a well defined time-frame during which evolution can occur which is defined by radiometric datings of the island and the geographical isolation from continental source areas which reduces gene flow between progenitor an derivative. All such factors combine favorably to enhance the suitability of island evolutionary investigations. In the current research project the endemic vascular flora of Ullung Island was studied. The island is located 150 km east of the Korean peninsula. Although the island is only 1.8 million years old, 28 endemic angiosperms exist here. Studies completed in the first phase of the Ullung Island project have focused on two endemic species of Acer and the endemic Hepatica maxima. By using DNA markers the progenitors for all three taxa could be determined. In all cases the progenitors apparently came from peninsular Korea and not from other geographical regions like Japan or China. Additional support was derived from cytological investigations, which could demonstrate specific structural features on chromosome 6 of the endemic Hepatica maxima. This structural feature is also found in Korean populations of Hepatica but is absent in all other species including accessions from Japan. Analysis of population structure in endemic populations of Acer revealed a high degree of similarity when compared with progenitor taxa which is probably explainable by the comparably young age of the island. Accordingly, the endemic taxa are currently in the first stages of speciation, which is also indicated by the absence of further species having evolved from already established endemic taxa. Population structure of the endemic species of Acer reveales an interesting contrast. Whereas in one case, the endemic populations are clearly monophyletic and have apparently come from a single origin from peninsular Korea, the other case shows a more complex pattern. At least two mainland populations have contributed to the evolution of the endemic taxon. The data suggest that during speciation genetic exchange between island and mainland populations must have been possible more than once.