Abstract
AbstractUnder the neutral theory, species with larger effective population sizes are expected to harbour higher genetic diversity. However, across a wide variety of organisms, the range of genetic diversity is orders of magnitude more narrow than the range of effective population size. This observation has become known as Lewontin’s paradox and although aspects of this phenomenon have been extensively studied, the underlying causes for the paradox remain unclear. Norway spruce (Picea abies) is a widely distributed conifer species across the northern hemisphere and it consequently plays a major role in European forestry. Here, we use whole-genome re-sequencing data from 35 individuals to perform population genomic analyses inP. abiesin an effort to understand what drives genome-wide patterns of variation in this species. Despite having a very wide geographic distribution and an enormous current population size, our analyses find that genetic diversity ofP.abiesis low across a number of populations (p=0.005-0.006). To assess the reasons for the low levels of genetic diversity, we infer the demographic history of the species and find that it is characterised by several re-occurring bottlenecks with concomitant decreases in effective population size can, at least partly, provide an explanation for low polymorphism we observe inP. abies. Further analyses suggest that recurrent natural selection, both purifying and positive selection, can also contribute to the loss of genetic diversity in Norway spruce by reducing genetic diversity at linked sites. Finally, the overall low mutation rates seen in conifers can also help explain the low genetic diversity maintained in Norway spruce.
Publisher
Cold Spring Harbor Laboratory