One-time duplication and ongoing loss of mitochondrial tRNA genes in Cryptocercus cockroaches.

Mitochondrial genome is a popular marker in phylogenetics and species diversity estimations. Mitogenome is relatively compact and conserved, while gene rearrangements were found in some species across various organisms. Models to explain the origin and evolution of gene rearrangement have been proposed but seldom demonstrated; empirical evidence from closely related species is particularly scarce. Here, through an intensive case study of the cockroach genus Cryptocercus Scudder, 1862, we elucidate the evolution of mitochondrial gene order. This study utilized 51 new samples and re-assembled raw reads of 26 published samples. A diversity of rearrangement patterns is recovered, especially in the tRNA gene cluster between ND3 and ND5, which is effectively explained by the duplication-random loss model. Specifically, the entire tRNA gene cluster was duplicated; this duplication is potentially facilitated by chance binding between the 3' end of ND5 gene and the ND3-trnA region during DNA replication. Furthermore, we reveal that one of the gene copies degenerated stochastically across lineages, directly contributing to the observed diversity in gene arrangement. Gene rearrangement patterns are apomorphies for certain clades, providing additional evidence for the inferred phylogeny and serving as potential indicators of species. This study underscores the importance of intensive sampling and rigorous data curation for deciphering the evolutionary mechanisms.