Mitogenomics of recombinant mitochondrial genomes of Baltic Sea Mytilus mussels

Abstract

Recombination in the control region (CR) of Mytilus mitochondrial DNA (mtDNA) was originally reported based on the relatively short, sequenced fragments of mitochondrial genomes. Recombination outside the CR has been reported recently with the suggestion that such processes are common in Mytilus. We have fully sequenced a set of 11 different mitochondrial haplotypes representing the high diversity of paternally inherited mitochondrial genomes of Baltic Sea Mytilus mussels, including the haplotype close to the native Mytilus trossulus mitochondrial genome, which was thought to have been entirely eliminated from this population. Phylogenetic and comparative analysis showed that the recombination is limited to the vicinity of the CR in all sequenced genomes. Coding sequence comparison indicated that all paternally inherited genomes showed increased accumulation of nonsynonymous substitutions, including the genomes which switched their transmission route very recently. The acquisition of certain CR sequences through recombination with highly divergent paternally inherited genomes seems to precede and favor the switch, but it is not a prerequisite for this process. Interspecies hybridization in the Baltic Sea during the recent 10,000 years created conditions for both structural and evolutionary mitochondrial instability which resulted in the observed variation and dynamics of mtDNA in Baltic Sea Mytilus mussels. In conclusion, the data shows that the effects of mitochondrial recombination are limited to the CR of few phylogenetic lineages.Electronic supplementary materialThe online version of this article (doi:10.1007/s00438-014-0888-3) contains supplementary material, which is available to authorized users.

Mitogenomics of southern hemisphere blue mussels (Bivalvia: Pteriomorphia): Insights into the evolutionary characteristics of the Mytilus edulis complex

“…The lowest dN/dS was detected for the Cox1 gene (Fig. 3B), which is in agreement with previous findings in M. edulis and M. galloprovincialis 222326 and may be explained by the highly conservative nature of this gene, as observed in other mollusks e.g 43…”

“…3A; Supplementary Table S2). Similar results have been reported in other marine mussels in which an accelerated accumulation non-synonymous substitutions was detected only at terminal branches of the phylogenetic trees22. This finding was also consistent with our GA-Branch analysis, particularly for the clade that includes all of the representative species of the M. edulis complex (Figure not shown).…”

“…The clade of the blue mussels was recovered as sister to the clade containing the northern Pacific California ( M. californianus ) and the Korean ( M. coruscus ) mussels (Fig. 4), which is congruent with previous phylogenetic works with complete mitochondrial genomes2223.…”

“…In our sequenced species, this region is located between the l-rRNA and tRNA-Tyr genes, with a length of 1,173 pb (Table 2 and Fig. 2A), which is in the range size of those observed among closely related species22232646, and almost twice longer than that of other Pteriomorphia species3542. This difference in the POR size could be explained by deletions or duplications of tandem sections3543 or by the high rate of divergence of the variable domains of this region reported for the genus Mytilus47.…”

“…Previous phylogenetic studies about the evolutionary relationships among Mytilus spp. have suggested that Southern Hemisphere mussels could be closely related to those mussels in the M. edulis complex of the Northern Hemisphere in which M. edulis and M. galloprovincialis are sister taxa, whereas M. trossulus is more distantly related518212223.…”