Data from: Genomic dissection of variation in clutch size and egg mass in a wild great tit (Parus major) population

Clutch size and egg mass are life history traits that have been extensively studied in wild bird populations, as life history theory predicts a negative trade-off between them, either at the phenotypic or genetic level. Here, we analyse the genomic architecture of these heritable traits in a wild great tit (Parus major) population, using three marker-based approaches - chromosome partitioning, quantitative trait locus (QTL) mapping and a genome-wide association study (GWAS). The variance explained by each great tit chromosome scales with predicted chromosome size, no location in the genome contains genome-wide significant QTL, and no individual SNPs are associated with a large proportion of phenotypic variation, all of which may suggest that variation in both traits is due to many loci of small effect, located across the genome. There is no evidence that any regions of the genome contribute significantly to both traits, which combined with a small, non-significant, negative genetic covariance between the traits, suggests the absence of genetic constraints on the independent evolution of these traits. Our findings support the hypothesis that variation in life history traits in natural populations is likely to be determined by many loci of small effect spread throughout the genome, which are subject to continued input of variation by mutation and migration, although we cannot exclude the possibility of an additional input of major effect genes influencing either trait.窝卵数与卵重是野生鸟类种群中被广泛研究的生活史性状，因为生活史理论预测二者在表型或遗传层面均存在负向权衡。本研究以野生大山雀（Parus major）种群为对象，采用三种基于分子标记的分析方法——染色体分区分析、数量性状基因座（quantitative trait locus, QTL）定位以及全基因组关联研究（genome-wide association study, GWAS）——解析这两个可遗传性状的基因组架构。研究发现，大山雀各染色体所解释的遗传方差与预测的染色体大小呈正相关；基因组中未存在达到全基因组显著水平的QTL，且单个单核苷酸多态性（single nucleotide polymorphism, SNP）位点均无法解释大部分表型变异，上述结果均表明两种性状的变异源于分布于全基因组的众多微效基因座。未发现基因组中存在可同时对两种性状产生显著贡献的区域，结合二者间微弱且未达显著水平的负遗传协方差，这提示两种性状的独立进化不存在遗传约束。本研究结果支持下述假说：自然种群中生活史性状的变异大概率由分布于全基因组的众多微效基因座所决定，这类基因座的变异会持续通过突变与迁移不断产生；不过本研究无法排除存在额外的主效基因影响其中任一性状的可能性。