Ivana Gudelj abstract
Biosciences, University of Exeter
The role of trade-offs in the evolution of diversity and host specialisation
Organisms cannot excel at all things but are obliged to be jack-of-all trades. This constraint is central to the concept of trade-offs. A bacteria, for example, cannot both grow extremely fast and be resilient to harmful substances; if it invests more into one it must invest less into the other. A seminal theoretical solution first formalized by Levins almost 50 years ago showed that, in theory, the geometry of a trade-off should determine how the species will respond over time to selection. A plethora of subsequent theories would be nullified were it be proven that Levins’ seminal postulate were not true. Unfortunately, because of the technical difficulty in doing the necessary tests this theory has gone untested. Using a combination of synthetic ecology and mathematical modeling we provide the first verification, showing that the exact form of the trade-off determines, in a predictable way, the outcome of evolution. But are trade-offs the answer to all our evolutionary problems? In particular we consider the question: why are most parasites specialists, able to infect only a small number of hosts? Host-use trade-offs have become a mainstay of theoretical explanations for the prevalence of host specialism, but empirical evidence for such trade-offs is rare. We propose an alternative theoretical approach based on basic features of the parasite life cycle showing how the tendency for relatively narrow host ranges in parasites can be explained even in the absence of trade-offs.