Felix Rico, Marianthi Karageorgi, Geno Guerra, Amy P. Hastings, Julianne N. Pelaez, Noah K. Whiteman, Kirsten I. Verster, Susanne Dobler, Fidan Sumbul, Simon C. Groen, Anurag Agrawal, Teruyuki Matsunaga, Jessica Aguilar, Susan L. Bernstein, Michael Astourian, University of California [Berkeley] (UC Berkeley), University of California (UC), Adhésion et Inflammation (LAI), Aix Marseille Université (AMU)-Assistance Publique - Hôpitaux de Marseille (APHM)-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS), Cornell University [New York], Universität Hamburg (UHH), ANR-10-EQPX-0029,EQUIP@MESO,Equipement d'excellence de calcul intensif de Mesocentres coordonnés - Tremplin vers le calcul petaflopique et l'exascale(2010), ANR-15-CE11-0007,BioHSFS,Développement et application de la spectroscopie de forces à haute vitesse pour la biologie(2015), European Project: 772257,MechaDynA, University of California [Berkeley], University of California, and Assistance Publique - Hôpitaux de Marseille (APHM)-Institut National de la Santé et de la Recherche Médicale (INSERM)-Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS)
Identifying the genetic mechanisms of adaptation requires the elucidation of links between the evolution of DNA sequence, phenotype, and fitness1. Convergent evolution can be used as a guide to identify candidate mutations that underlie adaptive traits2–4, and new genome editing technology is facilitating functional validation of these mutations in whole organisms1,5. We combined these approaches to study a classic case of convergence in insects from six orders, including the monarch butterfly (Danaus plexippus), that have independently evolved to colonize plants that produce cardiac glycoside toxins6–11. Many of these insects evolved parallel amino acid substitutions in the α-subunit (ATPα) of the sodium pump (Na+/K+-ATPase)7–11, the physiological target of cardiac glycosides12. Here we describe mutational paths involving three repeatedly changing amino acid sites (111, 119 and 122) in ATPα that are associated with cardiac glycoside specialization13,14. We then performed CRISPR–Cas9 base editing on the native Atpα gene in Drosophila melanogaster flies and retraced the mutational path taken across the monarch lineage11,15. We show in vivo, in vitro and in silico that the path conferred resistance and target-site insensitivity to cardiac glycosides16, culminating in triple mutant ‘monarch flies’ that were as insensitive to cardiac glycosides as monarch butterflies. ‘Monarch flies’ retained small amounts of cardiac glycosides through metamorphosis, a trait that has been optimized in monarch butterflies to deter predators17–19. The order in which the substitutions evolved was explained by amelioration of antagonistic pleiotropy through epistasis13,14,20–22. Our study illuminates how the monarch butterfly evolved resistance to a class of plant toxins, eventually becoming unpalatable, and changing the nature of species interactions within ecological communities2,6–11,15,17–19. CRISPR–Cas9 engineering of the Drosophila Atpα gene (encoding the α-subunit of the sodium pump) is used to study the ability of mutations that evolved independently in several insect orders to confer resistance to keystone plant toxins.