Mitochondrial genome evolution in Annelida: A systematic study on conservative and variable gene orders and the factors influencing its evolution

The mitochondrial genomes of Bilateria are relatively conserved in their protein-coding, rRNA and tRNA gene complement, but the order of these genes can range from very conserved to very variable depending on the taxon. The supposedly conserved gene order of Annelida has been used to support the placement of some taxa within Annelida. Recently, authors have cast doubts on the conserved nature of the annelid gene order. Various factors may influence gene-order variability including, among others, increased substitution rates, base composition differences, structure of non-coding regions, parasitism, living in extreme habitats, short generation times and biomineralization. However, these analyses were neither done systematically, nor based on well-established reference trees. Several focused on only a few of these factors and biological factors were usually explored ad-hoc without rigorous testing or correlation analyses. Herein, we investigated the variability and evolution of the anneli...