Title: Within and between species variation in the effect of new mutations

Abstract

What effect do new mutations have on fitness? This question is central to our understanding of many evolutionary topics, such as the rate of adaptive evolution, the genetic architecture of quantitative traits, and patterns of polymorphism and divergence. Recent work has attempted to characterise variation in the average effect of new mutations among species; however, little is known about the causes of this variation, and whether such variation could exist at multiple levels of evolution. We have addressed both of these question by characterising the distribution of fitness effects of new mutations for both multiple species and multiple populations of European trees, which were broadly sampled over their latitudinal ranges. We were able to investigate whether variation in the distribution of fitness effects of new mutations varies with level of population differentiation, genome structure or genetic background. Surprisingly, we found that recent events, such as demographic processes, generally have little effect on the distribution of fitness effects of new mutations, and instead variation in this important evolutionary parameter appears to be primarily driven by deep features of species biology.