Phylogeography and arctic biodiversity: a review

Current concerns over the impact that anthropogenic global climate change w ill have on levels of biodiversity have focused mainly on tropical and temp erate systems. Recently, attention has turned to polar systems, and the pot ential impacts these climatic changes might have on polar flora and fauna. Polar organisms have been subjected to dramatic fluctuations in environment al conditions during the Holocene and Pleistocene, so one might expect thes e systems to be resilient. However, little is really known of how such glob al climate changes will impact biodiversity in the arctic. What is known, p articularly through the use of molecular markers, is that glacial cycles ha ve impacted the evolutionary trajectories of many extant polar species. By studying these organisms, particularly those found across the Holarctic, on e can examine the dynamic interaction between deterministic forces (e.g. se lection) and historical processes (e.g., vicariance event) in order to bett er understand how these processes have impacted the phylogeography and gene tic divergence among taxa. Keeping with the "northern dimensions" theme of this symposium, we review results obtained from a variety of phylogeographi c studies that have examined the importance of dispersal, vicariance, and s election in shaping the distributions of arctic biota, especially among clo sely-related species complexes. In particular, we examine the recent debate over the importance of Pleistocene glacial cycles in influencing populatio n genetic differentiation and speciation. Finally, we provide an assessment of how studying these arctic systems will benefit the global perspective o n climate change research.