Rearrangements and accelerated mutation rates on Dendrodorididae mitogenomes rumble their evolution

The systematics of the family Dendrodorididae poses a challenge to evolutionary biologists, as their mitochondrial and nuclear markers provide contradictory phylogenetic signals. Nuclear pseudogenes or exogenous contamination are hypothesized to cause the molecular discordance. However, these hypotheses have not been tested. We used genomic data from seven Dendrodorididae species to investigate the evolution of this family. Two mitogenomes displayed a novel structural rearrangement in nudibranchs, involving the translocation of three collinear genes and five surrounding tRNAs. Additionally, we found numerous mitogenomic regions with non-synonymous mutations and multiple indels in both coding and ribosomal genes. Protein modeling resulted in similar structures, suggesting that functionality is conserved. Phylogenies using mitogenomic data confirmed a specific clade membership for the rearranged mitogenomes. The incorporation of nuclear data did not fully resolve the systematic relationships of Dendrodorididae, acknowledging the evolutionary complexity of this group. The present study provides novel evidence on sudden molecular changes in mitogenomes, and highlights the relevance of using genomic data to unveil rare evolutionary processes, which is critical for understanding evolution of neglected taxa.