Figure 5. Schematic scenario reconciling the discordance of the mtDNA gene tree with the species tree.

Grey bars represent the species tree, thick black lines the mtDNA gene tree, and black wedges denote mtDNA clades within each species. The cross symbolises the hypothesized disappearance of the autochthonous Daphnia pulicaria’s mtDNA in North America due to its replacement with that of Daphnia pulex. The arrows indicate the direction of this ancient mtDNA introgression as well as of a more recent introgression of the haplotypes from the NAPX clade.