Karageorgi, M., Groen, S.C., Sumbul, F., Pelaez, J.N., Verster, K.I., Aguilar, J.M., Hastings, A.P., Bernstein, S.L., Matsunaga, T., Astourian, M., Guerra, G., Rico, F., Dobler, S., Agrawal, A.A., Whiteman, N.K. (2019). Genome editing retraces the evolution of toxin resistance in the monarch butterfly.  Nature 574(7778): 409--412.

FBrf0244002

Research paper

Identifying the genetic mechanisms of adaptation requires the elucidation of links between the evolution of DNA sequence, phenotype, and fitness[1]. Convergent evolution can be used as a guide to identify candidate mutations that underlie adaptive traits[2-4], and new genome editing technology is facilitating functional validation of these mutations in whole organisms[1,5]. 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 toxins[6-11]. 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 glycosides[12]. Here we describe mutational paths involving three repeatedly changing amino acid sites (111, 119 and 122) in ATPα that are associated with cardiac glycoside specialization[13,14]. 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 lineage[11,15]. We show in vivo, in vitro and in silico that the path conferred resistance and target-site insensitivity to cardiac glycosides[16], 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 predators[17-19]. The order in which the substitutions evolved was explained by amelioration of antagonistic pleiotropy through epistasis[13,14,20-22]. 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 communities[2,6-11,15,17-19].

PMC7039281 (PMC) (EuropePMC)