Figure 2

Reconstruction of mitochondrial genome rearrangements for Nautilus macromphalus. At the top is the nearly complete gene arrangement for Phoronis architecta [11], a presumed outgroup to the mollusks, shown to polarize two of the cephalopod rearrangements: Having trnP in opposite orientation to nad6 and nad1 is the ancestral condition, as is having trnD between cox2 and atp8. The only two differences between the chiton Katharina tunicata [28] and the two octopus species is the inversion of trnP in the octopus and the transposition of trnD in the chiton. (No attempt is being made here to reconstruct all of the rearrangements between the phoronid and the chiton.) The arrangement found in the N. macromphalus, then, can be reconstructed by the additional switch in order of two large blocks of genes plus transpositions of trnF and trnT. Genes are not drawn to scale and are abbreviated as in Fig. 1 except that underlining signifies right-to-left transcriptional orientation. All genomes are circular and only graphically linearized at an arbitrarily chosen point. These genomes are chosen to illustrate the paucity of rearrangements in these particular lineages. The cuttlefish and several squid with complete mtDNA sequences (see text) have experienced many rearrangements unique to their lineages, and these patterns are reconstructed by Akasaki et al. [31].