Max Planck Research Group Evolutionary and Integrative Physiology

Our research group is focused on understanding how evolution happens as process.

This can be challenging because the evolutionary process for a given trait has only run once and one occurrence does not provide much information about dynamics. Therefore, our approach is to examine the independent evolution of similar adaptive outcomes in different lineages. Given an understanding of the genetics behind a given trait, convergent evolution can be a powerful tool for addressing questions about the dynamics of the adaptive process.

The evolution of resistance to widespread toxins of the cardiotonic steroid family represents one of the best studied examples of adaptive molecular evolution. Hundreds of plants and animals across the globe have evolved chemical defense through synthesis or sequestration of cardiotonic steroid. In response, many herbivores and predators have developed resistance to these toxins through target-site insensitivity of cardiotonic steroids’ target protein, the Na,K-ATPase. This adaptation has been repeatedly achieved by amino acid substitutions at the same sites in the cardiotonic steroid binding pocket of Na,K-ATPase, demonstrating remarkable patterns of convergence, divergence, and parallelism in evolution. We have leveraged this model system to answer key questions about the dynamics of the adaptive process.

Questions and methods

How predictable are adaptations? We assess the available paths that can lead to cardiotonic steroid resistance. Although this adaptation is often achieved by mutations at the same sites on the Na,K-ATPase, the mutations themselves can differ from one species to another. The question then becomes whether each species’ mutational outcome was simply a result of chance or whether other molecular forces influenced the accessibility of these outcomes.

How accessible are adaptations? We test the extent to which evolutionary paths are constrained by a mechanism known as “intramolecular epistasis”, wherein a mutation only produces an adaptive change if it occurs on the right genetic background. A big implication of epistasis is that the accumulated history of mutations in the past for a given lineage may influence the allowable mutations in the future. By assessing the effects of mutations on different genetic backgrounds and at different points in evolutionary time, we are teasing apart the extent to which this mechanism has constrained and shaped this adaptation.

What effects does gaining adaptations have on other traits? We study how an otherwise beneficial mutation may be associated with “negative pleiotropy" – meaning that adaptive changes to one trait can cause correlated changes to other traits that may be detrimental to fitness. By assessing the mechanisms that allow organisms to relieve these negative effects, such as compensatory mutations and/or gene duplications, we am teasing apart the ways in which the evolution of cardiotonic steroid resistance has been shaped by them.