Aberrant Mitochondrial tRNA Genes Appear Frequently in Animal Evolution.

Mitochondrial tRNAs have acquired a diverse portfolio of aberrant structures throughout metazoan evolution. With the availability of more than 12,500 mitogenome sequences, it is essential to compile a comprehensive overview of the pattern changes with regard to mt-tRNA repertoire and structural variations. This, of course, requires reanalysis of the sequence data of more than 250,000 mt-tRNAs with a uniform workflow. Here, we report our results on the complete reannotation of all mitogenomes available in the RefSeq database by September 2022 using mitos2. Based on the individual cases of mt-tRNA variants reported throughout the literature, our data pinpoint the respective hotspots of change, i.e. Acanthocephala (Lophotrochozoa), Nematoda, Acariformes and Araneae (Arthropoda). Less dramatic deviations of mt-tRNAs from the norm are observed throughout many other clades. Loss of arms in animal mt-tRNA clearly is a phenomenon that occurred independently many times, not limited to a small number of specific clades. The summary data here provide a starting point for systematic investigations into the detailed evolutionary processes of structural reduction and and loss of mt-tRNAs as well as a resource for further improvements of annotation workflows for mt-tRNA annotation.