Large-scale chromosome rearrangements are arguably the most dramatic type of mutations, often leading to rapid evolution and speciation. However, chromosome dynamics at the sequence level have only been studied in a small number of model systems. In insects, comparative genomics has revealed high levels of chromosome conservation in Diptera (flies and mosquitoes) and Lepidoptera (butterflies and moths). Whether this truly reflects the diversity of insect genome evolution is questionable, given that many non-model species exhibit rapid karyotype evolution. Diverse karyotypes have been reported in Hemiptera, particularly aphids, which are important plant pests. Here, we generated high-quality chromosome-scale genome assemblies of the green peach aphid (Myzus persicae) and the pea aphid (Acyrthosiphon pisum) that belong to the tribe Macrosiphini, and compared these to a previously published chromosome-scale assembly of the corn-leaf aphid (Rhopalosiphum maidis) of the tribe Aphidini. We find that aphid autosomes are highly rearranged, but that the gene content of the aphid sex (X) chromosome is conserved, remaining unchanged over 30 million years, despite rapid sequence evolution, low gene expression and high transposable element load. To test whether rapid evolution of genome structure is a hallmark of Hemiptera, we compared our aphid assemblies to recently released chromosome-level assemblies of two blood-feeding hemipteran species (Rhodnius prolixus and Triatoma rubrofasciata). Despite being more diverged, both blood-feeding hemipterans show high synteny with only two chromosome fusion or fission events detected. The exceptional rate of structural evolution of aphid autosomes renders them an important emerging model system for studying the role large-scale genome rearrangements in evolution.
Less...