Haplotype Median Joining network for the 16S ribosomal RNA haplotypes of Potamopyrgus antipodarum. Haplotypes are represented by black circles, the size of which is proportional to the number of populations in which a particular haplotype is present. Populations are listed in Table 2. Haplotypes are from #1 to #22; white circles without a number indicate a hypothetical intermediate haplotype linking observed haplotypes. Hatch marks in the network represent single mutations.