Lepidopteran Synteny Units (LSUs) reveal deep conservation of macrosynteny in butterflies and moths

Advances in DNA sequencing technologies have, for the first time, provided us with enough whole chromosome-level genomes to understand in detail how chromosome number and composition change over time. Here, we use the genomes of butterflies and moths to look at the levels and age of macrosynteny in the Lepidoptera and Trichoptera. We used comparative BUSCO analsysis to define reproducible units of macrosynteny which we term Lepidopteran Synteny Units or LSUs. The 31 chromosomes of the model butterfly Melitaea cinxia served as a reference point. The results show that chromosome-wide macrosynteny extends from the most basal branches of the Lepidopteran phylogeny to the most distal. This synteny also extends to the order Trichoptera, a sister group of the Lepidoptera. Thus, chromosome-wide macrosynteny has been conserved for a period of >200 My in this group of insects. We found no major interchromosomal translocations, reciprocal or non-reciprocal, in the genomes studied. Intrachromosomal rearrangements, in contrast, were abundant. Beyond its use in defining LSUs, this type of homology-based analysis will be useful in determining the relationships between chromosomal elements in different animals and plants. Further, by more precisely defining the breakpoints of chromosomal rearrangements we can begin to look at their potential roles in chromosomal evolution. StatementThe authors declare no conflicting interests ContributionsConceptualisation: W.T., R.H.f.; data analysis: W.T.; writing & editing: W.T., K.S., R.H.f All authors read and approved the final manuscript.