Complete Genome of Achalarus lyciades, The First Representative of the Eudaminae Subfamily of Skippers

BACKGROUND: The Hoary Edge Skipper (Achalarus lyciades) is an eastern North America endemic butterfly from the Eudaminae subfamily of skippers named for an underside whitish patch near the hindwing edge. Its caterpillars feed on legumes, in contrast to Grass skippers (subfamily Hesperiinae) which feed exclusively on monocots. RESULTS: To better understand the evolution and phenotypic diversification of Skippers (family Hesperiidae), we sequenced, assembled and annotated a complete genome draft and transcriptome of a wild-caught specimen of A. lyciades and compared it with the available genome of the Clouded Skipper (Lerema accius) from the Grass skipper subfamily. The genome of A. lyciades is nearly twice the size of L. accius (567 Mbp vs. 298 Mbp), however it encodes a smaller number of proteins (15881 vs. 17411). Gene expansions we identified previously in L. accius apparently did not occur in the genome of A. lyciades. For instance, a family of hypothetical cellulases that diverged from an endochitinase (possibly associated with feeding of L. accius caterpillars on nutrient-poor grasses) is absent in A. lyciades. While L. accius underwent gene expansion in pheromone binding proteins, A. lyciades has more opsins. This difference may be related to the mate recognition mechanisms of the two species: visual cues might be more important for the Eudaminae skippers (which have more variable wing patterns), whereas odor might be more important for Grass skippers (that are hardly distinguishable by their wings). Phylogenetically, A. lyciades is a sister species of L. accius, the only other Hesperiidae with a complete genome. CONCLUSIONS: A new reference genome of a dicot-feeding skippers, the first from the Eudaminae subfamily, reveals its larger size and suggests hypotheses about phenotypic traits and differences from monocot-feeding skippers.