Genotypes, phenotypes and Fisher's geometric model
Fisher's geometric model (FGM) was originally introduced to argue that complex adaptations must occur in small steps because of pleiotropic constraints. When supplemented with the natural assumption of additivity of mutational effects on phenotypic traits, it provides a versatile and conceptually simple mechanism for the emergence of genotypic epistasis from the nonlinear mapping of phenotypes to fitness. In the talk I will present the results of a recent study of pairwise epistasis between randomly chosen beneficial mutations in a multicellular fungus, which provides support for the predictions of FGM and allows to estimate the model parameters from data. To put these results into context, I then describe theoretical work aimed at clarifying the relationship between genotypic and phenotypic complexity in the model. The talk is based on joint work with Sungmin Hwang, Su-Chan Park, Sijmen Schoustra and Arjan de Visser.