Genetic drift outweighs natural selection at toll-like receptor (TLR) immunity loci in a re-introduced population of a threatened species
Genetic drift outweighs natural selection at toll-like receptor (TLR) immunity loci in a re-introduced population of a threatened species
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DOI：
10.1111/mec.12404
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发表时间：
2013-09-01
影响因子：
4.9
通讯作者：
Jamieson, Ian G.
中科院分区：
文献类型：
--
作者：
Grueber, Catherine E.;Wallis, Graham P.;Jamieson, Ian G.
在种群建立过程中，遗传漂变可能是遗传多样性变化的关键驱动力，特别是在种群较小的情况下。然而，自然选择也可以发挥作用，在塑造多样性的功能重要的基因座。我们使用了一个经过充分研究，重新引入人口的威胁斯图尔特岛知更鸟（N=722个纯种个体），以确定是否选择形先天免疫toll样受体（TLR）基因的遗传多样性，在9年的人口增长期后，建立12个遗传创始人。我们没有发现任何证据的选择操作方面的TLR多样性的第一年越冬生存的大多数位点，基因型和等位基因的研究。然而，TLR 4（BE）基因型个体的存活率显著提高：与所有其他TLR 4基因型相比，这些鸟类在成熟前死亡的可能性不到一半。此外，该基因型的人口频率，超过Hardy-Weinberg预期的两倍，增加了非随机交配。近乎完整的采样和完整的系谱和生殖数据使我们能够消除这些模式的其他潜在原因，包括近亲繁殖，年份效应，密度依赖性，在早期生活史阶段对动物的选择或TLR 4（E）等位基因与良好基因的基因组水平关联。然而，观察到的基因多样性水平的预测模拟遗传漂变的比较显示，结果与中性预期的所有位点，包括TLR 4。虽然选择有利于TLR 4（BE）杂合子在这个群体中，这些影响不足以超过遗传漂变。这是第一个实证研究表明，遗传漂变可以压倒自然选择在一个野生种群建立后立即。
During population establishment, genetic drift can be the key driver of changes in genetic diversity, particularly while the population is small. However, natural selection can also play a role in shaping diversity at functionally important loci. We used a well-studied, re-introduced population of the threatened Stewart Island robin (N=722 pedigreed individuals) to determine whether selection shaped genetic diversity at innate immunity toll-like receptor (TLR) genes, over a 9-year period of population growth following establishment with 12 genetic founders. We found no evidence for selection operating with respect to TLR diversity on first-year overwinter survival for the majority of loci, genotypes and alleles studied. However, survival of individuals with TLR4(BE) genotype was significantly improved: these birds were less than half as likely to die prior to maturity compared with all other TLR4 genotypes. Furthermore, the population frequency of this genotype, at a two-fold excess over Hardy-Weinberg expectation, was increased by nonrandom mating. Near-complete sampling and full pedigree and reproductive data enabled us to eliminate other potential causes of these patterns including inbreeding, year effects, density dependence, selection on animals at earlier life history stages or genome-level association of the TLR4(E) allele with good genes'. However, comparison of observed levels of gene diversity to predictions under simulated genetic drift revealed results consistent with neutral expectations for all loci, including TLR4. Although selection favoured TLR4(BE) heterozygotes in this population, these effects were insufficient to outweigh genetic drift. This is the first empirical study to show that genetic drift can overwhelm natural selection in a wild population immediately following establishment.