Genomes of Two Flying Squid Species Provide Novel Sights into Adaptations of Cephalopods to Pelagic Life

Pelagic cephalopods have evolved a series of fascinating traits, such as excellent visual acuity, high-speed agility, and photophores for adaptation to open pelagic oceans. However, the genetic mechanisms underpinning these traits are not well understood. Thus, in this study, we obtained high-quality genomes of two purpleback flying squid species (Sthenoteuthis oualaniensis and Sthenoteuthis sp.), with sizes of 5450 and 5651 Mb. Comparative genomic analyses revealed a common expansion of the S-crystallin subfamily SL20-1 associated with visual acuity in the purpleback flying squid lineage and showed that evolution of high-speed agility for the species was accompanied by significant positive selection pressure on genes related to energy metabolism. These molecular signals might have contributed to the evolution of their adaptative predatory and anti-predatory traits. In addition, transcriptomic analysis provided clear indications of the evolution for the photophores of purpleback flying squids, inter alia that recruitment of new genes and energy metabolism genes may have played key functional roles in the process.