gene flow (Bernatchez & Wilson 1998; Colbourne et al.
1998; Waters et al. 2001). Recently, evidence of ecologi- cally-based speciation has been revealed in a variety of freshwater species and geographic settings (Lu & Ber- natchez 1999; Rundle et al. 2007; Schluter & Conte
2009). These finding reinvigorated the long-lasting debate on the relative contribution of geography and ecology to diversification in the freshwater realm. For organisms with exceptionally high dispersal abilities and a cyclically parthenogenetic mode of reproduction, such as anomopod cladocerans, continuous range expansion or colonization of novel aquatic habitats (e.g. habitat transitions) can potentially initiate speciation through a combination of founder effect, natural selection (Lynch 1985; De Meester 1996; Pfrender et al.
2000), and hybridization (Taylor & Hebert 1993).