Data_Sheet_1_Natural and Artificial Selection for Parasitoid Resistance in Drosophila melanogaster Leave Different Genetic Signatures.xlsx

Adaptation of complex traits depends on standing genetic variation at multiple loci. The allelic variants that have positive fitness effects, however, can differ depending on the genetic background and the selective pressure. Previously, we interrogated the Drosophila melanogaster genome at the population level for polymorphic positions and identified 215 single nucleotide polymorphisms (SNPs) that had significantly changed in frequency after experimental evolution for increased parasitoid resistance. In the current study, we follow up on 11 of these SNPs as putative targets of the experimental selection process (Jalvingh et al., 2014). We study the patterns of genetic variation for these SNPs in several European field populations. Furthermore, we associate the genetic variation of these SNPs to variation in resistance against the parasitoid Asobara tabida, by determining the individual phenotype and SNP genotype for 144 individuals from four Selection lines and four non-selected Control lines and for 400 individuals from 12 Field lines that differ in parasitoid resistance. For the Selection lines we additionally monitored the changes in allele frequencies throughout the five generations of experimental selection. For three genes, mbl (Zn-finger protein), mthl4 (G-protein coupled receptor) and CG17287 (protein-cysteine S-palmitoyltransferase) individual SNP genotypes were significantly associated with resistance level in the Selection and Control lines. Additionally, the minor allele in mbl and mthl4 were consistently and gradually favored throughout the five generations of experimental evolution. However, none of these alleles did appear to be associated to high resistance in the Field lines. We suggest that, within field populations, selection for parasitoid resistance is a gradual process that involves co-adapted gene complexes. Fast artificial selection, however, enforces the sudden cumulating of particular alleles that confer high resistance (genetic sweep). We discuss our findings in the context of local adaptation.

复杂性状的适应性演化依赖于多基因座的现存遗传变异。然而，具有正向适合度效应的等位基因变异，其效应会因遗传背景与选择压力的不同而存在差异。此前，我们在种群水平上对黑腹果蝇（Drosophila melanogaster）基因组的多态位点进行了筛查，鉴定出215个单核苷酸多态性（single nucleotide polymorphisms, SNPs），这些位点在针对寄生蜂抗性提升的实验演化过程中频率发生了显著变化。本研究中，我们聚焦其中11个SNPs，将其作为实验选择过程的推定靶标（Jalvingh等，2014）。我们对多个欧洲野外种群中这些SNPs的遗传变异模式展开了研究。此外，我们通过对4个选择系、4个未选择对照组的144个个体，以及12个寄生蜂抗性存在差异的野外种群系的400个个体的表型与SNP基因型进行鉴定，将这些SNPs的遗传变异与宿主对寄生蜂（Asobara tabida）的抗性变异进行关联分析。针对选择系，我们还监测了整轮5代实验选择过程中等位基因频率的变化情况。在选择系与对照组中，有3个基因——mbl（锌指蛋白，Zn-finger protein）、mthl4（G蛋白偶联受体，G-protein coupled receptor）以及CG17287（蛋白质-半胱氨酸S-棕榈酰转移酶，protein-cysteine S-palmitoyltransferase）——的个体SNP基因型与抗性水平存在显著关联。此外，在整轮5代实验演化过程中，mbl与mthl4的次要等位基因始终受到逐步的选择青睐。然而，在野外种群系中，这些等位基因均未表现出与高抗性存在关联。我们认为，在野外种群中，针对寄生蜂抗性的选择是一个渐进过程，涉及共适应基因复合体。而快速的人工选择则会促使赋予高抗性的特定等位基因快速累积（遗传清扫，genetic sweep）。我们将结合局部适应性的研究背景对本研究结果展开讨论。