Retrospective coalescent methods and the reconstruction of metapopulation histories in the sea |
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Authors: | Peter B Marko Michael W Hart |
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Institution: | (1) Department of Biological Sciences, Clemson University, Clemson, SC 29634, USA;(2) Department of Biological Sciences, Simon Fraser University, Burnaby, BC, V5A 1S6, Canada |
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Abstract: | Phylogeographic analyses are a key interface between ecological and evolutionary ways of knowing because such analyses integrate
the cumulative effects of demographic (ecological) processes over geological (evolutionary) time scales. Newly developed coalescent
methods allow evolutionary ecologists to overcome some limitations associated with inferring population history from classic
methods such as Wright’s F
ST. Here we briefly contrast classic and coalescent methods for looking backward in time through a population genetic lens,
focusing on the key advantages of the isolation-with-migration (IM) class of coalescent methods for distinguishing ancient
connectedness from actual recurrent contemporary gene flow as causes of genetic similarity or differentiation among populations.
Making this critical distinction can lead to the discovery of otherwise obscured histories underlying conventional patterns
of spatial variation. We illustrate the importance of these insights using analyses of Pacific fishes, snails, and sea stars
in which population sizes and divergence times are more important than rates of contemporary gene flow as determinants of
population genetic differentiation. We then extend the IM method to genetic data from two model metapopulation species (California
abalone, Australian damselfish). The analyses show the potential use of non-equilibrium IM methods for differentiating among
metapopulation models that make different predictions about population parameters and have different implications for the
design of marine protected areas and other conservation goals. At face value, the results largely rule out classic metapopulation
dynamics (dominated by extinction and colonization rather than connectivity via ongoing recurrent gene flow) but, at the same
time, do not strongly support a modern marine metapopulation dynamic (ecologically significant connectivity between demes).
However, the results also highlight the need for much more data (i.e., loci) sampled on different spatial scales in order
to determine whether metapopulation dynamics might exist on smaller scales than are typically sampled by most phylogeographers
and landscape geneticists. |
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