Whether speciation can advance to completion in the face of initially high levels of gene flow is a very controversial topic in evolutionary biology. Extensive gene exchange is generally considered to homogenize populations and counteract divergence. Moreover, the role of introgressive hybridization in evolution remains largely unexplored in animals, particularly in freshwater zooplankton in which allopatric speciation is cons...

Previous mitochondrial (mt)DNA sequencing and restriction fragment length polymorphism (RFLP) studies have shown that the Holarctic Daphnia pulex complex is divisible into two major groups ( pulicaria and tenebrosa ) that exhibit distinct phylogeographic patterns. Here we examine allozymic variation at six polymorphic enzyme loci to ascertain clonal structure and clonal distribution patterns within each group. Specimens were c...