Phylogeography and arctic biodiversity: a circumpolar study of the Daphnia pulex complex

Lawrence J. Weider

The University of Oklahoma Biological Station, Kingston, Oklahoma, U.S.A

and

Anders Hobaek

Norwegian Institute for Water Research, Bergen, Norway

Pleistocene glaciations have impacted the evolutionary trajectories of many modern species, particularly those inhabiting polar regions.  By studying the organisms inhabiting polar regions of the Holarctic, one can examine the dynamic interaction between dispersal and vicariance and how these processes have impacted phylogeography and genetic divergence among taxa.  

Several features distinguish polar regions from their temperate and tropical counterparts.  Most notably, formerly glaciated polar regions are “younger”, having only recently been open for recolonization; therefore, such regions are further from an equilibrium condition than more southerly regions.  In effect, these regions allow one to examine the dynamic interactions of such forces as founder-flush effects, gene flow, and priority effects (i.e. preemptive competition), all of which will shape the population genetics and phylogeography of resident taxa.  

In collaboration with colleagues in Canada, here we present the results of a circumarctic study of  bio(genetic) diversity among members of  the Daphnia pulex complex, a dominant component of the zooplankton in arctic, boreal, and temperate aquatic habitats, globally.  Using a suite of techniques ranging from allozyme (protein) electrophoresis to mitochondrial (mt)DNA restriction fragment length polymorphism analysis (RFLPs) to  sequencing of portions of the mtDNA genome, we estimate levels of genetic (clonal) variation in this primarily asexual species complex.  We examine how dispersal of lineages via resistant resting eggs has permitted post-glacial colonization of many of the freshwater habitats in the Holarctic.  Further, based on our molecular markers, we make inferences about the positioning of putative glacial refugia and dispersal corridors.  

Finally, we compare and contrast our results with those from other phylogeographic studies that have examined the importance of dispersal and vicariance in shaping faunal distributions among closely-related species complexes.