Abstract
BackgroundMitochondrial (mt) gene arrangement is highly variable among molluscs and especially among bivalves. Of the 30 complete molluscan mt-genomes published to date, only one is of a heterodont bivalve, although this is the most diverse taxon in terms of species numbers. We determined the complete sequence of the mitochondrial genomes of Acanthocardia tuberculata and Hiatella arctica, (Mollusca, Bivalvia, Heterodonta) and describe their gene contents and genome organisations to assess the variability of these features among the Bivalvia and their value for phylogenetic inference.ResultsThe size of the mt-genome in Acanthocardia tuberculata is 16.104 basepairs (bp), and in Hiatella arctica 18.244 bp. The Acanthocardia mt-genome contains 12 of the typical protein coding genes, lacking the Atpase subunit 8 (atp8) gene, as all published marine bivalves. In contrast, a complete atp8 gene is present in Hiatella arctica. In addition, we found a putative truncated atp8 gene when re-annotating the mt-genome of Venerupis philippinarum. Both mt-genomes reported here encode all genes on the same strand and have an additional trnM. In Acanthocardia several large non-coding regions are present. One of these contains 3.5 nearly identical copies of a 167 bp motive. In Hiatella, the 3' end of the NADH dehydrogenase subunit (nad)6 gene is duplicated together with the adjacent non-coding region. The gene arrangement of Hiatella is markedly different from all other known molluscan mt-genomes, that of Acanthocardia shows few identities with the Venerupis philippinarum. Phylogenetic analyses on amino acid and nucleotide levels robustly support the Heterodonta and the sister group relationship of Acanthocardia and Venerupis. Monophyletic Bivalvia are resolved only by a Bayesian inference of the nucleotide data set. In all other analyses the two unionid species, being to only ones with genes located on both strands, do not group with the remaining bivalves.ConclusionThe two mt-genomes reported here add to and underline the high variability of gene order and presence of duplications in bivalve and molluscan taxa. Some genomic traits like the loss of the atp8 gene or the encoding of all genes on the same strand are homoplastic among the Bivalvia. These characters, gene order, and the nucleotide sequence data show considerable potential of resolving phylogenetic patterns at lower taxonomic levels.
Highlights
Mitochondrial gene arrangement is highly variable among molluscs and especially among bivalves
Metazoan mitochondrial genomes are typically conserved in gene content and length
The high number of possible arrangements makes it very unlikely that identical gene orders arise by chance [2]
Summary
Mitochondrial (mt) gene arrangement is highly variable among molluscs and especially among bivalves. The high number of possible arrangements makes it very unlikely that identical gene orders arise by chance [2]. Such a complex character combined with a low frequency of gene rearrangements is highly valuable for reconstructing palaeozoic or even preCambrian phylogenetic events. Only 30 complete mitochondrial genomes of Mollusca are published: ten Gastropoda, nine Bivalvia, one Polyplacophora, two Scaphopoda and eight Cephalopoda Even this small taxonomic sample reveals much greater variability of gene arrangements compared to vertebrates and arthropods and notable differences in rearrangement frequencies between phyla and within the Mollusca [3]. Whereas the order of the protein coding and the rRNA (rrn) genes in the mt genomes of the polyplacophoran Katharina tunicata, the vetigastropod Haliotis rubra and the cephalopods Octopus vulgaris and Octopus ocellatus are identical and the apogastropod Ilyanassa obsoleta and the other cephalopods can be related to them, the euthyneuran gastropods, the scaphopods and the bivalves are highly rearranged
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.