Data from: Drift and selection influence geographic variation at immune loci of prairie-chickens

Previous studies of immunity in wild populations have focused primarily on genes of the major histocompatibility complex (MHC); however, studies of model species have identified additional immune-related genes that also affect fitness. In this study, we sequenced five non-MHC immune genes in six greater prairie-chicken (Tympanuchus cupido) populations that have experienced varying degrees of genetic drift as a consequence of population bottlenecks and fragmentation. We compared patterns of geographic variation at the immune genes with six neutral microsatellite markers to investigate the relative effects of selection and genetic drift. Global FST outlier tests identified positive selection on just one of five immune genes (IAP-1) in one population. In contrast, at other immune genes, standardized G′ST-values were lower than those at microsatellites for a majority of pairwise population comparisons, consistent with balancing selection or with species-wide positive or purifying selection resulting in similar haplotype frequencies across populations. The effects of genetic drift were also evident as summary statistics (e.g., Tajima’s D) did not differ from neutrality for the majority of cases, and immune gene diversity (number of haplotypes per gene) was correlated positively with population size. In summary, we found that both genetic drift and selection shaped variation at the five immune genes, and the strength and type of selection varied among genes. Our results caution that neutral forces, such as drift, can make it difficult to detect current selection on genes.过往针对野生种群免疫相关性状的研究，主要聚焦于主要组织相容性复合体（major histocompatibility complex）相关基因；然而模式物种的相关研究已证实，其他若干免疫相关基因同样会对适合度产生影响。本研究对6个大草原松鸡（Tympanuchus cupido）种群的5个非MHC免疫基因进行了测序，这些种群因经历种群瓶颈与生境破碎化，出现了不同程度的遗传漂变。本研究将免疫基因的地理变异模式与6个中性微卫星标记进行对比分析，以解析选择作用与遗传漂变的相对影响效应。全局FST（Fixation index，遗传分化系数）离群值检测仅在1个种群中，发现5个免疫基因中的1个（IAP-1）受到正选择作用。与之形成鲜明对比的是，在绝大多数成对种群比较中，其余免疫基因的标准化G′ST值均低于微卫星标记的对应值，这一结果与平衡选择，或是全物种范围内的正选择/纯化选择所导致的种群间单倍型频率趋同现象相符。遗传漂变的效应同样显著：多数情况下，群体遗传学汇总统计量（如塔伊马D统计量（Tajima’s D））与中性进化预期无显著差异，且免疫基因多样性（单倍型数/基因）与种群规模呈显著正相关。综上，本研究发现遗传漂变与选择共同塑造了5个免疫基因的变异模式，且选择的强度与类型因基因而异。本研究结果提示，诸如漂变这类中性进化力量，会显著增加检测当前基因上选择作用的难度。