Title Testing the Coastal Refuge Hypothesis: Comparative Phylogeography of Three Mammals in the Alexander Archipelago of the North Pacific

Key Words: Island Systems, Endemism, Alexander Archipelago, Phylogeography

During the last glacial maximum (LGM), southcoastal Alaska was covered by ice sheets, but isolated coastal refugia have been hypothesized (3). As the glaciers receded about 10,000ybp, plants and animals are thought to have re-colonized the region from refugial populations along the North Pacific Coastisl and populations and also refugia south (e.g. Oregon) and north (e.g. Beringia) of the region (3, 13). This resulted in admixture of divergent source populations and high levels of island endemism.

Island systems often support genetically distinct populations due to prolonged isolation from the mainland. In many cases, these systems are also rich in cryptic species, key components to biodiversity (1). Effects of island size and isolation on species richness and evolution in tropical systems provide textbook examples in ecology and evolution; however, these relationships in northern latitude archipelagos are less known. The biogeographical history of island systems has significant impact on genetic structure of insular populations. But the relationship of distance (among islands and between the mainland) and genetic structure and its effects on endemism are not well studied. Because changes in environmental conditions may elevate extinction risk, owing to small populations, modest ranges, and limited mobility, understanding these systems is essential to preserve ecosystem services (10, 12, 14, 16).

With 2000 named islands, including 7 of the 15 largest US islands, the Alexander Archipelago (AA) of Alaska is one of the planet’s most extensive archipelagos, but has not been well studied. The AA is part of the largest temperate rainforest in the world and includes the Tongass National Forest, our largest National Forest. The Tongass has been exploited by logging companies, with more than 70% old growth forest removed to date (10). The AA is considered an evolutionary hot spot due to a complex history of glaciation, resulting in unique patterns of endemism and evolutionary divergence (5).

I became interested in phylogeography when I began my work as a research assistant at the University of Miami. The practical application and broader goal associated with such an evolutionary genetic approach caught my attention; the ability to identify climatic change that lead to species differentiation and use this knowledge in habitat preservation. For my PhD, I will explore general principles of molecular evolution with regard to insularity and divergence. I will examine the historical biogeography, geographic structure and connectivity of three wide-spread sympatric species: Sorex monticolus (dusky shrew), Peromyscus keeni (Keen’s mouse), and Microtus longicaudus (long-tailed vole). These species have high potential for endemism, and zones for each were identified where distinctive lineages have expanded (4, 6, 11).

I hypothesize that 1) these sympatric species will share patterns of genetic structure related to the geographic history of the archipelago, including the signature of a hypothesized coastal refugium, 2) genetic divergence will increase relative to island isolation and 3) contact zones will provide insight into the colonization by coastal populations through distinct genetic signatures. For finer scale analyses to assess corridors for species movement, contact zones and proposed barriers (3) I will reconstruct island connectivity based on bathymetric projections. These reconstructions will show sea level changes during the LGM, thus exposing more land surface (14). The laboratory skills I gained as a research assistant at the University of Miami, along with my field experience acquired summer of 2007, will contribute to my ability to address these questions.

Preliminary studies using mitochondrial DNA identified many island endemics and significant inter-island diversification in mammals (4, 6, 7, 11). However, larger sample sizes and independent evidence (e.g. nuclear loci) are required to further investigate the evolutionary history and relative connectivity among populations (2). I will analyze 590 archived samples from the University of Alaska and Museum of Southwestern Biology at the University of New Mexico. Additional samples will be collected in the field from focal areas, chosen based on proposed refugia, island size, and isolation. Collection of samples will follow the Institutional Animal Care and Use Committee (IACUC) animal subject protocols, enforced by the University of New Mexico. Lab work will follow standard protocols for DNA extraction, amplification and sequencing. Analyses will include a population genetics approach using Fu’s Fs, coalescent theory (8, 9), and STRUCTURE, as well as Bayesian phylogenetic approaches for both intra- and interspecific analysis. I will analyze 5 different nuclear DNA loci for 20 different populations (n=10) of each species within the AA to pinpoint colonization events, population range expansion and diversification in fragmented landscapes.

In addition to testing the impact of historical geologic events on geographic structure, inferences from these three species can be used to understand whether endemic plants and animals are vulnerable to change from increased logging practices coupled with other anthropogenic impacts (e.g. roads, introduction of invasive species), and climate change. I will present guidelines related to spatial endemism within the AA (and extended it to other island systems or fragmented habitats) to improve existing management programs on the Tongass National Forest and conserve vulnerable species and island ecosystems.

As part of this project, I am already mentoring an underrepresented undergraduate, and will eventually involve high school students, in genetic laboratory techniques and experiences. The results of this study will be submitted to high impact scientific journals, presented at symposiums and shared with agencies and policy makers responsible for forest management. This study has practical applications to improvement of ecology management strategies and the development of Pleistocene parks.

Literature Cited

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