Absence of strong signal of background selection affecting nucleotide diversity in Drosophila pseudoobscura

Nucleotide variation correlates positively with regional rates of recombination in the genomes of many species, and intensive effort has been devoted to deciphering the evolutionary forces driving this association. The effects of sweeps associated with the spread of advantageous mutations and background selection associated with the removal of detrimental mutations are exceedingly hard to decouple. Here, we examine patterns of nucleotide variation in a subset of Drosophila pseudoobscura genes that are unlikely to have been affected by one extreme class of selective sweeps, and test for residual signal that may be attributable to background selection. While our statistical power is low due to the number of genes fitting our criteria and small numbers of sequences, the proportion of variation explained by our tests is extremely low and sometimes opposite in direction of predictions of background selection. We tentatively conclude that most of the association of nucleotide variation with r...