Mitogenome sequence comparison in the endangered congeneric Pinna nobilis and Pinna rudis bivalves

The pen shells Pinna nobilis and Pinna rudis are large wedge-shaped bivalve molluscs. Both species are threatened by different anthropogenic pressures. In the last few years, P. nobilis populations have significantly reduced due to massive mortality events. The complete mitochondrial DNA sequences of these congeneric species have been determined and compared for the first time.

The mitogenome sequences of P. nobilis and P. rudis were 18,919 bp and 18,264 bp in length, respectively. Each mitogenome is composed of 12 protein-coding genes, 2 ribosomal RNA, 22 transfer RNA (tRNAs) genes and non-coding regions. A putative Adenosine Triphosphate synthase subunit 8 gene could only be proposed for P. nobilis. Both newly sequenced mitogenomes present a conserved gene order between them, comparable to the closely related Atrina pectinata, but global arrangement greatly differs from other available bivalve mitochondrial sequences. Multiple copies of tRNA-Cys were identified, located in different positions probably due to mechanisms of mitochondrial genome rearrangements, and detected 2 and 3 times in P. rudis and in P. nobilis, respectively.

A close relationship was shown between Pinna species and Atrina pectinata and a consistent clustering showing a monophyletic origin of Pinnidae family sequences was evidenced. The mitochondrial genomes will provide a valuable genetic resource for further studies on population genetics and species identification.