Gene duplications during experimental evolution of Caenorhabditis elegans : duplication rates and evolutionary responses

Copy-number variants (CNVs) are a ubiquitous form of genetic variation. How often this form of variation arises and its adaptive significance are active areas of contemporary research. This work presents evidence regarding both of these subjects. First, it demonstrates that gene duplications occur at a frequency two orders of magnitude greater than point mutations. Specifically, the gene duplication rate is estimated to be 1.2 x 10-7/gene/generation, compared to a point mutation rate on the order of ~10-9/site/ generation. Second, it was found that populations in a low state of fitness due to mutation accumulation could recover some or all of their fitness over short spans of generations concurrent with an increase in frequency of duplications and deletions that arose during the recovery process. The pattern of frequency increase among CNVs over generations during recovery was consistent with the signature of positive selection. The median size of duplications that were identified after selection for ~200 generations were significantly larger (191.5 kb) than both duplications that occurred spontaneously (2 kb) in the absence of selection and deletions identified after selection for ~200 generations (12.5 kb). The median number of genes contained in the duplications during recovery was 38, evincing the ability of these events to increase the genetic information available for selection to act on. These results clearly demonstrate that gene duplication and deletion processes contribute significantly to the adaptability of populations