There are several ways in which organisms can evolve in order to survive environmental changes. One is to adapt to novel conditions by natural selection; another is to evolve phenotypic plasticity that can accommodate a predictable change of conditions. But when conditions change sufficiently rapidly or unpredictably, a third strategy is predicted to evolve: adaptive bet-hedging. A bet-hedger pays a cost in short term fitness in order to reduce variance in fitness across many generations, maximising long term geometric mean fitness, rather than arithmetic mean fitness. Adaptive bet-hedging is supported by strong theory, with roots in insurance and gambling, but it’s difficult to study in biological systems because many generations are needed to see its benefit.
An interesting example of bet-hedging is chromosome mis-segregation in yeast, which causes gain or loss of individual chromosomes, that is, aneuploidy. Aneuploid cells typically grow slower than cells with the normal chromosome number, but they can survive extreme environmental stresses, including antibiotics. Aneuploidy is heritable but reversible, acting like a phenotypic switch, so consensus chromosome number is maintained in long term evolution. In this project, you will genetically manipulate chromosome mis-segregation rates and determine the short term and long term fitness effects in environments with different regimes of unpredictability. Chromosomes will be marked fluorescently, allowing their evolutionary fate to be determined. Experimental results will be compared with theoretical predictions. The project will include wet lab genetics and experimental evolution (Greig) as well as theory and quantitative modelling (Shou).