Reconstructing the history of intercontinental dispersal in Daphnia lumholtzi by use of genetic markers

After its appearance in 1989, the cladoceran Daphnia lumholtzi rapidly disp ersed throughout the southern United States. In the current study, we used allozyme and mitochondrial deoxyribonucleic acid sequence data to infer the past dispersal of this species. Both genetic markers revealed the similari ty among all U.S. populations and those from Uganda and Nepal but their div ergence from Australian lineages. The extent of genetic divergence among po pulations, when coupled with estimates of rates of molecular evolution, sug gests that the distribution of this species reflects a series of long-dista nce dispersal events over the last 4 million years.