Convergent evolution offers powerful opportunities to understand when and why evolution repeatedly arrives at similar solutions. Convergence is rarely unconstrained: molecular architecture, physiological trade-offs, and ecological context can all limit the range of viable adaptive pathways. Our research uses the evolution of toxicity and toxin resistance as a model to uncover the molecular rules that shape convergent evolutionary change.

We use cardiotonic steroids, which are potent plant-derived toxins that target the Na, K-ATPase, an essential and highly conserved enzyme. Across insects and vertebrates, resistance to these toxins has evolved repeatedly, often through a small number of recurrent amino-acid substitutions. We investigate how these repeated solutions arise, which alternatives are inaccessible, and how molecular constraint channels evolution along predictable paths.

Using chemically defended insects like large milkweed bugs, we examine how variation in toxin sequestration and composition interacts with predator pressure, warning signals, and physiological costs. At the molecular level, we analyse the evolution of Na⁺/K⁺-ATPase gene families and functionally characterise resistance-conferring mutations to assess their effects on enzyme performance and organismal fitness.

By linking molecular mechanisms to ecological interactions and evolutionary outcomes, our work aims to reveal how constraint, trade-offs, and evolutionary history shape adaptive landscapes, and why evolution so often converges on the same molecular solutions.