Data from: Heterozygosity predicts clutch and egg size but not plasticity in a house sparrow population with no evidence of inbreeding

We investigated the link between heterozygosity and the reaction norm attributes of reproductive performance in female house sparrows (Passer domesticus). We collected data on clutch size, egg size, hatching success, and nestling survival in 2 816 nesting attempts made by 791 marked individuals over a 16 year period. Pedigree analysis revealed no evidence of inbreeding. Neither parent-offspring regression nor an animal model revealed significant heritability in clutch or egg size. We selected 42 females that laid at least seven clutches at our study site and used a survey of 21 autosomal microsatellite loci to estimate heterozygosity for each female. We controlled for phenotypic plasticity and found that both clutch and egg size showed significant positive correlations with heterozygosity. We found no evidence that heterozygosity influenced the slope of individual reaction norms. Further analysis suggested that clutch size was affected by heterozygosity across the genome, but egg size had more complex relationships, with evidence favoring the influence of multiple loci. Given the apparent lack of inbreeding and large population size, our results suggest associative overdominance as the likely mechanism for the impact of heterozygosity, but also created a puzzle about the process producing associations between neutral markers and the genes affecting clutch size or egg size. One possible explanation is a long term residual effect of the historical bottleneck that occurred when house sparrows were introduced into North America. The existence of HFCs in a population with considerable phenotypic plasticity and little inbreeding implies that the effects of heterozygosity may be more significant than previously thought.本研究针对雌性家麻雀（Passer domesticus）的杂合性（heterozygosity）与繁殖表现反应规范（reaction norm）属性之间的关联展开了调查。我们在16年的研究周期内，针对791只已标记个体的2816次筑巢尝试，收集了窝卵数、卵大小、孵化成功率以及雏鸟存活率相关数据。谱系分析未发现近交迹象。无论是亲子回归分析还是动物模型分析，均未发现窝卵数与卵大小存在显著遗传力。我们筛选出42只在研究区域内至少产下7窝卵的雌性个体，通过对21个常染色体微卫星位点的检测，估算了每只个体的杂合性。我们对表型可塑性（phenotypic plasticity）进行了控制，结果显示窝卵数与卵大小均与杂合性呈现显著正相关。未发现杂合性对个体反应规范的斜率存在显著影响。进一步分析表明，窝卵数受全基因组杂合性的影响，而卵大小的关联机制更为复杂，现有证据支持多位点效应的作用。鉴于研究种群几乎不存在近交且规模较大，本研究结果提示关联超显性（associative overdominance）可能是杂合性产生影响的潜在机制，但同时也引出了一个未解之谜：中性标记与影响窝卵数或卵大小的基因之间的关联是通过何种过程形成的。一种可能的解释是，家麻雀被引入北美时经历的历史种群瓶颈效应所留下的长期残留影响。在表型可塑性较强且近交程度较低的种群中发现杂合性-适合度相关性（HFCs，heterozygosity-fitness correlations），意味着杂合性的作用可能比此前预想的更为重要。