Data from: The Red Death meets the abdominal bristle: polygenic mutation for susceptibility to a bacterial pathogen in Caenorhabditis elegans

Understanding the genetic basis of susceptibility to pathogens is an important goal of medicine and of evolutionary biology. A key first step toward understanding the genetics and evolution of any phenotypic trait is characterizing the role of mutation. However, the rate at which mutation introduces genetic variance for pathogen susceptibility in any organism is essentially unknown. Here we quantify the per-generation input of genetic variance by mutation (VM) for susceptibility of Caenorhabditis elegans to the pathogenic bacterium Pseudomonas aeruginosa (defined as the median time of death, LT50). VM for LT50 is slightly less than VM for a variety of life-history and morphological traits in this strain of C. elegans, but is well within the range of reported values in a variety of organisms. Mean LT50 did not change significantly over 250 generations of mutation accumulation. Comparison of VM to the standing genetic variance (VG) implies a strength of selection against new mutations of a few tenths of a percent. These results suggest that the substantial standing genetic variation for susceptibility of C. elegans to P. aeruginosa can be explained by polygenic mutation coupled with purifying selection.

解析病原体易感性状的遗传基础，是医学与进化生物学的重要研究目标。解析任意表型性状的遗传与演化机制的关键第一步，是解析突变的作用。然而，目前学界对任意生物体中，突变为病原体易感性状引入遗传方差的速率仍基本未知。本研究针对秀丽隐杆线虫（Caenorhabditis elegans）受致病性细菌铜绿假单胞菌（Pseudomonas aeruginosa）感染的易感程度（以半数致死时间LT50定义），量化了其每代由突变引入的遗传方差（VM）。该品系秀丽隐杆线虫的LT50对应的VM，略低于其多种生活史与形态性状的VM，但仍处于多个已报道物种的VM取值范围内。在250代突变积累（mutation accumulation）过程中，群体平均LT50未发生显著变化。将VM与现存遗传方差（standing genetic variance, VG）进行比较后，可推导出针对新发突变的选择强度约为百分之零点几。上述结果表明，秀丽隐杆线虫对铜绿假单胞菌易感性状的大量现存遗传变异，可通过多基因突变与纯化选择（purifying selection）共同作用得到合理解释。