Department of Mathematics Colloquium

University of Idaho

Spring 2012

Thursday,  March 22, 3:30-4:20 pm, room TLC 032

Refreshments in Brink 305 at 3:00 pm

Mutational Effects and Population Dynamics during
Viral Adaptation Challenge Current Models


Paul Joyce

Department of Mathematics, Department of Statistics

University of Idaho


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.