Comparative insect mitochondrial genomes: Differences despite conserved genome synteny

We present a comparative analysis of select insect mitochondrial DNA (mtDNA) representing four insect orders (Diptera, Hymenoptera, Orthoptera and Coleoptera) consisting of 12 different species in an effort to study a common set of genes and to understand the evolution of mitochondrial genome. A functional analysis of mitochondrial genomes was carried out using ERGO bioinformatics suite. To compare the similarity between closely related insect mitochondrial genome sequences, dot-plot comparisons of sequences were performed. LSU and SSU rRNA sequences were used to construct a phylogenetic tree to determine the relationship among four insect orders. LSU rRNA sequences yielded a tree with branching patterns reflecting the expected pattern as insect species belonging to different orders were put into separate clades. Based on the sequence similarity, insect species belonging to four different orders in general appear to be closely related. However, a comparative and functional analysis of insect mitochondria sequences revealed differences in gene organization of mtDNA. Although tRNA species were identical in most species of insects, their position and the transcription orientations were different, reflecting differential transcriptions. Based on this study we conclude that, although the gene types are very similar across these insect orders, significant differences in GC content perhaps suggest multiple mitochondrial ancestors.