Tracing the Paleogeographical History of Hawaii

One way to trace the paleographical history of a landmass or archipelago is the reconstruction of the phylogeny of its organisms, by means of DNA sequence analysis. For example, if the closest living relatives of a group of species found on the Galapagos Islands occur in Peru, it can be assumed that for these group of organisms, colonization took place from somewhere in central western South America. This might vary between groups of organisms, since each group has different means of dispersal and mobility. Lichens, or correctly lichenized fungi, are believed to evolve more slowly than plants and animals and therefore, their phylogenetic relationships can reveal deeper levels of paleogeographical history among landmasses, archipelagos, and islands. In this project, we use lichens of the family Graphidaceae, which is the largest family of tropical lichens with possibly over 2000 species, to trace the paleogeographical history of the Hawaiian islands. A field expedition in collaboration with resident lichenologist Clifford Smith will gather fresh material of the roughly 100-200 species believed to occur on the islands. Extraction and sequencing of DNA will then reveal which are their closest living relatives and what their current distribution is. We expect to find three main patterns:

  • A small number of species which do not have a close living relative outside the islands and which, consequently, evolved and even diversified on the islands themselves, no being endemic to Hawaii.
  • A larger number of species which do have a close living relative outside the islands but with a restricted distribution; that distribution will then give us clues about the main origins of dispersal towards the islands and the possible dispersal routes.
  • A larger number of species that have a very wide (pantropical) distribution; in this case we can still trace origins and routes of dispersal because the phylogenetic relationships among specimens of the same species will give us clues. For example, specimens of a species found in Hawaii but also in tropical America, Africa, Asia, and Australia, may cluster in a way that the Hawaiian populations appear closest to American populations, then suggesting that colonization took place from the Americas.

The analysis of phylogenetic relationships will also give us hints about how often the islands were repeatedly colonized and which groups had more or less success in colonizing them. These results can then be correlated with specific features of the lichens, such as the type of spores or the type of microhabitat the lichens thrive in, which is supposed to either facilitate dispersal over long distances or make it more difficult.