WHAT CAN MOLECULAR MARKERS TELL US ABOUT THE EVOLUTIONARY HISTORY OF DAPHNIA SPECIES COMPLEXES

Despite the wealth of information on the ecology of Daphnia species, t he systematics and phylogeny of the genus is still unresolved. The tax onomic uncertainties are based in part on the phenomenon of interspeci fic hybridization, which has been well documented for species of the D . galeata/cucullata/hyalina complexes. The occurrence of syntopic popu lations of up to three species and their three hybrids suggest niche d ifferentiation, but very little is known about genetic divergence of h ybridizing taxa and the potential consequences of hybridization (i.e. introgression). Since an operational species definition is necessarily based on information on the evolutionary mechanisms that result into the splitting of lineages, ecological and genetic consequences of inte rspecific hybridization have to be considered. In order to reveal the significance of hybridization and introgression, we combined several a spects of phylogenetic investigations within the D. galeata/cucullata/ hyalina complexes. Furthermore we demonstrate how molecular markers co ntribute to an evaluation of species complexes.