Parallel molecular evolution in an herbivore community

The gene encoding the sodium–potassium pump — the molecular target of the cardiac glycosides that milkweeds produce — was sequenced across many insect lineages that feed on those plants and across relatives that do not.

Studied in

Insecta, Asclepias

Sample size

sequence comparison across insect lineages feeding on milkweeds

Insects from unrelated orders feeding on cardiac-glycoside plants repeatedly acquired substitutions at the same small set of sites in the same gene, with several identical changes arising independently.

• Sequence-level evidence of repeated substitution; the functional effect of each change is established for some sites and inferred for others.
• Concerns one toxin family and one molecular target, which is exactly why the constraint is so tight.

• Convergent evolution

  Unrelated insects feeding on milkweeds repeatedly acquired the same substitutions in the same protein — the pump the plant’s toxin attacks. They did not inherit the solution; there is barely another one.

• Convergent evolution

  When a trait evolves repeatedly, the same genes turn up far more often than chance would allow. The target is narrow: few genes can be altered to produce the trait without breaking something else.