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 noncoding 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 annelid gene order and the factors that potentially influenced its evolution, using a comprehensive and systematic approach. The analyses were based on 170 genomes, including 33 previously unrepresented species. Our analyses included 706 different molecular properties, 20 life-history and ecological traits, and a reference tree corresponding to recent improvements concerning the annelid tree. The results showed that the gene order with and without tRNAs is generally conserved. However, individual taxa exhibit higher degrees of variability. None of the analyzed life-history and ecological traits explained the observed variability across mitochondrial gene orders. In contrast, the combination and interaction of the best-predicting factors for substitution rate and base composition explained up to 30% of the observed variability. Accordingly, correlation analyses of different molecular properties of the mitochondrial genomes showed an intricate network of direct and indirect correlations between the different molecular factors. Hence, gene order evolution seems to be driven by molecular evolutionary aspects rather than by life history or ecology. On the other hand, variability of the gene order does not predict if a taxon is difficult to place in molecular phylogenetic reconstructions using sequence data or not. We also discuss the molecular properties of annelid mitochondrial genomes considering canonical views on gene evolution and potential reasons why the canonical views do not always fit to the observed patterns without making some adjustments.publishedVersio

Description of a new species of the genus Marphysa (Eunicidae), Marphysa aegypti sp.n., based on molecular and morphological evidence

The annelid family Eunicidae comprises ten genera including the genusMarphysa Quatrefages, 1866. This genus is characterized by a global distribution and hasconsiderable value in the bait industry worldwide. Therefore, the correct delimitation ofspecies is important not only for consideration of its evolution, but also for culturing speciesfrom this genus. Marphysa sanguinea (Montagu, 1813) represents a complex of species andits global distribution is not clearly defined. Herein we describe a new species, Marphysaaegypti sp.n., belonging to the M. sanguinea group from the coastal waters of Egypt. Thisspecies, which has previously been reported as M. sanguinea, has a high commercial valueas it is collected and vastly used by fishermen in Egypt. In our study, we used both molecular(COI barcoding region) and morphological species identification. Our results confirm thatthis polychaete, which is a common inhabitant of Egyptian coastal waters (i.e., Mediterra-nean Sea, Red Sea and the Suez Canal), is a distinct species. Our findings further supportthe view that the polychaete fauna of Egypt needs taxonomic revision. Determination of thepolychaete species of Egypt, similarly to other regions of the world, is based on identifica-tion keys developed for Northern European species and lacks thorough morphologicalcomparisons. Therefore, all previous records of M. sanguinea in coastal waters of Egyptshould be reconsidered as being indeed M. aegypti sp.n