Frequent assimilation of mitochondrial DNA by grasshopper nuclear genomes

Multiple copies of mitochondrial-like DNA were found in the brown mountain grasshopper, Podisma pedestris (Orthoptera: Acrididae), paralogous to COI a nd ND5 regions. The same was discovered using the ND5 regions of nine other grasshopper species from four separate subfamilies (Podisminae, Calliptami nae, Crytacanthacridinae, and Gomphocerinae). The extra ND5-like sequences were shown to be nuclear in the desert locust, Schistocerca gregaria (Cyrta canthacridinae), and probably so in P. pedestris and an Italopodisma sp. (P odisminae), Eighty-seven different ND5-like nuclear mitochondrial pseudogen es (Numts) were sequenced from 12 grasshopper individuals. Different nuclea r mitochondrial pseudogenes, if descended from the same mitochondrial immig rant, will have diverged from each other under no selective constraints bec ause of their loss of functionality. Evidence of selective constraints in t he differences between any two Numt sequences (e.g., if most differences ar e at third positions of codons) implies that they have separate mitochondri al origins. Through pairwise comparisons of pseudogene sequences, it was es tablished that there have been at least 12 separate mtDNA integrations into P. pedestris nuclear genomes. This is the highest reported rate of horizon tal transfer between organellar and nuclear genomes within a single animal species. The occurrence of numerous mitochondrial pseudogenes in nuclear ge nomes derived from separate integration events appears to be a common pheno menon among grasshoppers. More than one type of mechanism appears to have b een involved in generating the observed grasshopper Numts.