Department of Mathematics Colloquium
|Adaptation by natural selection can follow a
stepwise process. At each step of adaptation a mutation arises,
the mutant has higher fitness than the wildtype, and the new mutations
fixes in the population. In this talk we explore the distribution
of first and second steps of adaption. For the viral data
under review we show that the distribution of first-step adaptive
mutations differed significantly from the distribution of second-steps,
and a surprisingly large number of second-step beneficial mutations
were observed on a highly fit first-step background.
We will discuss two commonly used mutational landscape models: the uncorrelated (rugged) landscape model and the additive (smooth) landscape model. Collectively, the results of the viral adaptation experiments indicate that the fitness landscape falls between the extremes of smooth and fully uncorrelated, violating the assumptions of many current mutational landscape models. However, a third explanation based on Fisher’s geometric model provides a better explanation of the data.