Comparative analysis of mitochondrial genomes between FCDK and FCSH
The mitochondrial genomes of both FCDK and FCSH share the ancestral gene order found in Pancrustracea. The genome sizes of the two strains were slightly different, at 15,141 bp for FCSH and 15,177 bp for FCDK, with a 36 bp insertion in the FCDK mitochondrial sequence between trnQ and trnM (Figure 5a, b). Fourteen out of 37 mitochondrial genes shared the same gene length in FCDK and FCSH. The overall sequence identity between the two mito-genomes was 78.2% (Figure 5c). The average pairwise identity was 77.13% for 13 CDSs, 87.0% for 22 tRNAs, 82.6% for 2 rRNAs, and 60.2% for the noncoding regions. The pairwise identity of the standard barcoding region (a 658 bp sequence in the 5’ region of the cox1 gene) in these two sibling species was 80.9%. Such great sequence divergence would be unlikely to be attributable to intraspecies variation. Strengthened by the mitochondrial genome analyses, FCDK and FCSH should be regarded as two distinct species.