The biogeography of Australian Daphnia: clues of an ancient (>70 m.y.) origin for the genus

Abstract

The Australian Daphnia (D. occidentalis, D. jollyi, D. lumholtzi, D. carinata, D. nivalis, and D. cephalata) include representatives from three distinct groups within the genus. The worldwide distribution of species within these three groups is consistent with a Gondwanan or pre-Gondwanan origin for each group. These data suggest an even more ancient origin for the genus Daphnia. The finding that D. cephalata must have been separated from D. carinata since Gondwanan times is consistent with recent biochemical data on the phylogenetic relations of Australian Daphnia, but contrasts with electrophoretic evidence of continuing hybridization between these two taxa. It is suggested that continued gene exchange between otherwise discrete species, or clonal complexes, of Daphnia may be maintained for millions of years, partly as a result of the varying degrees of cyclical parthenogenesis, and partly as a result of the highly fragmented population structures, found in these taxa.