Abstract

Behavioural ecologists use evolutionary theory to provide adaptive explanations for observations of animals living in their natural environment. Success relies on accurately identifying selection pressures acting upon traits of interest. For this reason, we have made limited progress in understanding the adaptive significance of behavioural traits in microbes. To observe a bacterial cell, we typically isolate it from its natural environment first before bringing it into the lab for examination. This process releases cells from the very selection pressures we wish to understand. Furthermore, the bacteria we are most interested in – human pathogens – live in one of the most inaccessible and irreplicable environments – living human beings. In this talk, I will present evidence that selection to optimise fitness from social interactions can drive long-term phenotypic dynamics in Pseudomonas aeruginosa infecting patients with cystic fibrosis. After ten years of studying P. aeruginosa in precisely controlled experimental evolution studies, we were interested to know if the competitive dynamics of co-operators and cheats in our experiments had any relevance to the real world. But first we had to overcome the challenge of identifying selection pressures inside a human lung.