Figure 4

Model for the evolution of mt genomes and DUI in Palaeoheterodonta. The backbone tree represents the phylogeny obtainable by removing the M mtDNAs from the trees in Fig. 2. DUI presence/absence is specified for all major clades. At the tip of each final branch, the names of the species for which we obtained the mtDNA sequences in this study are indicated together with the respective family (no species are enlisted for Unionidae); superfamily affiliations are specified with bars on the right side of the figure. Circles beside a final branch represent a schematic mt genome structure with the following colour code: black, mtDNA of a non-DUI species; red, F mtDNA in a DUI species/family; blue, M mtDNA in a DUI species/family. Purple circles in parentheses represent the typical H mtDNA of secondarily hermaphroditic species in a given family. For N. margaritacea mt genome, the interrogation point highlights the uncertain presence of DUI in this species, while the red colour the fact that the genome we obtained, if DUI is present, would be its F. Bars on the mtDNAs represent atp8-derived ORFs (green), M-orfs (blue), F-orfs (red), or H-orfs (purple), while blue triangles represent the elongated cox2 genes in M mtDNAs. The position of these latter features on the schematic mtDNAs reflects their actual location in the mt genomes (compare with Fig. 1). Bars inside the Unionida branches of the tree indicate evolutionary events and/or character states of lifestyle-related features as enlisted by ref. 14 (grey bars) or evolutionary events of mt genomes (black bars), described inside the figure.