Predictability in the evolution of Orthopteran cardenolide insensitivity

Abstract

The repeated evolutionary specialization of distantly related insects to cardenolide-containing host plants provides a stunning example of parallel adaptation. Hundreds of herbivorous insect species have independently evolved insensitivity to cardenolides, which are potent inhibitors of the alpha-subunit of Na + ,K + -ATPase (ATPα). Previous studies investigating ATPα-mediated cardenolide insensitivity in five insect orders have revealed remarkably high levels of parallelism in the evolution of this trait, including the frequent occurrence of parallel amino acid substitutions at two sites and recurrent episodes of duplication followed by neo-functionalization. Here we add data for a sixth insect order, Orthoptera, which includes an ancient group of highly aposematic cardenolide-sequestering grasshoppers in the family Pyrgomorphidae. We find that Orthopterans exhibit largely predictable patterns of evolution of insensitivity established by sampling other insect orders. Taken together the data lend further support to the proposal that negative pleiotropic constraints are a key determinant in the evolution of cardenolide insensitivity in insects. Furthermore, analysis of our expanded taxonomic survey implicates positive selection acting on site 111 of cardenolide-sequestering species with a single-copy of ATPα, and sites 115, 118 and 122 in lineages with neo-functionalized duplicate copies, all of which are sites of frequent parallel amino acid substitution. This article is part of the theme issue ‘Convergent evolution in the genomics era: new insights and directions’.

Molecular physiology of chemical defenses in a poison frog

“…Another transporter of note is the Na + /K + -ATPase pump, the beta 2 subunit expression of which was elevated in chemically defended wild-caught frogs compared with laboratory frogs. The Na + /K + -ATPase pump alpha subunit is a frequent target in the evolution of toxin resistance in a number of herbivorous invertebrates (Yang et al, 2019;Dobler et al, 2012) and vertebrates (Ujvari et al, 2015). Investigations of the function and evolution of the beta subunit in the context of toxin resistance is lacking.…”

Adaptive substitutions underlying cardiac glycoside insensitivity in insects exhibit epistasis in vivo

“…Support for this hypothesis comes from the fact that multiple insect species specializing on CGcontaining host-plants have independently duplicated and neofunctionalized ATPa1. In all cases examined to date, species with two or more copies retain one minimally altered copy that is more highly expressed in nervous tissue, and have evolved one or more insensitive copies that are more highly expressed in the gut, the site of absorption of CGs Yang et al 2019). Further support for negative pleiotropic effects is provided by the expression of engineered ATPa1 constructs in cell lines, suggesting that some duplicate-specific CG-insensitivity substitutions appear to reduce NKA activity (Dalla and Dobler 2016).…”

“…Despite this wide variety of potential paths to CG-insensitivity, the evolution of insensitivity in most CG-adapted insects is due, at least in part, to target-site insensitivity. Indeed, in most cases, diet specialization on CG-containing hostplants has been accompanied by recurrent adaptive amino acid substitutions to the CG-binding domain of the alpha-subunit of NKA, ATPa1 Dobler et al 2012;Yang et al 2019). Previous studies have identified up to 35 sites in ATPa1 at which substitutions could contribute to CG-insensitivity (reviewed in Zhen et al 2012).…”

“…This said, a model invoking serial substitution of A119S and compensatory mutations is not the only plausible scenario. Alternatively, since CG-insensitive haplotypes substitutions including A119S lack strong deleterious effects and may confer a survival advantage upon exposure to CGs when heterozygous ( Figure 3, Figure 4, Figure S8), such haplotypes may be maintained over time by heterozygote advantage and subsequently reach fixation as they accumulate a sufficient number of compensatory substitutions (Kimura 1985) or by gene duplication (Spofford 1969), which has occurred repeatedly in CG-specialist species Petschenka et al 2017;Yang et al 2019). Interestingly, D. subobscura is polymorphic for substitutions at positons 111 and 122 mediating CG-insensitivity and these haplotypes are associated with polymorphic inversions that may rarely be homozygous (Pegueroles et al 2016).…”

The Organ Distribution, Characterization and Modification of Acetylcholinesterase Activity in Adult African Grasshopper: Zonocerus sp Linn.

“…The major peak in the elution profile shows acetylcholinesterase activity of 0.280 M/min/ml. This shows considerable elution of the pure enzyme from its crude homogenate under considerable standard conditions [20].…”