The complete mitochondrial genomes of three species of Macridiscus Dall, 1902 (Bivalvia: Veneroidea: Veneridae) and their phylogenetic implications

摘要

The genus Macridiscus includes three species (M. melanaegis, M. multifarius and M. semicancellata) with similar morphology. They are endemic to the coastline of the western Pacific and are economically important. To analyse their phylogenetic relationships, we obtained complete mitochondrial (mt) genomes from each species by long and accurate polymerase chain reaction and primer walking sequencing. The mt genome sizes for M. melanaegis, M. multifarius and M. semicancellata are 20,738 bp, 20,171 bp and 20,189 bp, respectively. Length variation arises mainly from non-coding regions. Gene arrangement in the three Macridiscus mt genomes is the same, and three identical gene blocks are shared with the mt genome of Ruditapes philippinarum. Phylogenetic relationships between these three species and 24 other species in the order Veneroida inferred from 12 mt protein-coding genes suggest that R. philippinarum is the most closely related species to the Macridiscus species. Our coalescent dating analysis estimates that tMRCA for Macridiscus is 5.95 (95% HPD 4.46-7.65) Ma, and tMRCA for M. multifarius and M. semicancellata is 2.12 (95% HPD 1.54-2.90) Ma, indicating their speciation process might have been spurred by sea level changes during historical glaciations. Current patterns of distribution suggest that the Yangtze River discharge and its nearby salt marsh coastline might be a dispersal barrier for species in the Yellow Sea and in the East China Sea.