Strand Asymmetry in Crustacean Mitogenome as an Implication of Change in Substitution Pattern

Most animal mitochondrial genome exhibit strand asymmetry in nucleotide composition. Crustaceans represent a large diverse group of aquatic arthropods where the pattern of strand asymmetry is often violated with respect to the general pattern that is seen in most of the vertebrates and invertebrates. Most of the crustaceans show an overall strand asymmetry of negative GC skew, but AT skew varies randomly among species. Strand asymmetry in mitochondria is determined by the underlying spectrum of mutations. However, the substitution spectrum involved in crustacean mitogenome remains unclear. We present here a comparative analysis of various mitogenome features of 52 crustaceans' whole mitochondrial genome and elucidate the underlying substitution pattern. The observation reveals various asymmetries among the two strands and variation from the arthropod ground pattern as well. We found that substitution of adenine for guanine acts as the dominant phenomenon in shaping strand asymmetry in crustacean mitogenome. Moreover, the two strands show different bias for substitution pattern. And this phenomenon may have driven the translocation of the four genes (nad1, nad4, nad4l and nad5) in the minor coding strand in crustaceans and other invertebrates, which are otherwise located in the major coding strand in vertebrates. Additionally, the species that show wide variation in gene order from the crustacean ground pattern with a translocation or inversion of the control region seems to have different substitution pattern. Thus, our results demonstrate how the observed substitution pattern shapes various mitogenome features of crustaceans.