Data from: New ways to acquire resistance – Imperfect convergence in insect adaptations to a potent plant toxin

Evolution of insensitivity to the toxic effects of cardiac glycosides has
become a model in the study of convergent evolution, as five taxonomic
orders of insects use the same few similar amino acid substitutions in the
otherwise highly conserved Na,K-ATPase α. We here show that insensitivity
in pyrgomorphid grasshoppers evolved along a slightly divergent path. As
in other lineages, duplication of the Na,K-ATPase α gene paved the way for
subfunctionalization: one copy maintains the ancestral, sensitive state
while the other copy is resistant. Nonetheless, in contrast to all other
investigated insects, the grasshoppers’ resistant copy shows length
variation by two amino acids in the first extracellular loop, the main
part of the cardiac glycoside binding pocket. RT-qPCR analyses confirmed
this copy is predominantly expressed in tissues exposed to the toxins,
while the ancestral copy predominates in the nervous tissue. Functional
tests with genetically engineered Drosophila Na,K-ATPases bearing the
first extracellular loop of the pyrgomorphid genes showed the derived form
to be highly resistant, while the ancestral state is sensitive. Thus, we
report convergence in gene duplication and in the gene targets for toxin
insensitivity, however the means to the phenotypic end have been novel in
pyrgomorphid grasshoppers.