Department of Forest and Conservation Sciences, University of British Columbia, Vancouver, BC, Canada.
The Lab of Ornithology, Cornell University, Ithaca, NY.
J Hered. 2018 Jun 27;109(5):501-509. doi: 10.1093/jhered/esy027.
Variation in immune gene sequences is known to influence resistance to infectious diseases and parasites, and hence survival and mate choice, across animal taxa. Toll-like receptors (TLRs) comprise one essential gene family in the vertebrate innate immune system and recognize evolutionarily conserved structures from all major microorganism classes. However, the causes and consequences of TLR variation in passerine birds remain largely unexplored. We examined 7 TLR genes in song sparrows (Melospiza melodia), a species that is studied across North America. We then examined sequences from 4 unduplicated TLRs (TLR1LB, TLR3, TLR4, and TLR15) from birds in 2 parts of the species' range (N = 27, N = 6), tested for evidence of selection, and conducted pilot analyses of the role of TLR heterozygosity in survival. We identified 45 SNPs: 19 caused changes in amino acid sequences and 2 of these were likely deleterious. We found no evidence of codon-level episodic positive selection but detected purifying selection at codons in all TLRs. Contrary to expectations we found no strong correlation between heterozygosity at TLRs and inbreeding coefficient f (estimate ± standard error [SE] = -0.68 ± 0.37, Radj2 = 0.08, F1,25 = 3.38, P = 0.08). In addition, pilot analyses revealed no relationship between TLR heterozygosity and survival (β ± SE: 0.09 ± 2.00, P = 0.96), possibly due to small sample size. Further analyses of genetic diversity in TLRs are likely to advance understanding of the effects of innate immune gene diversity on the fitness and persistence of wild populations.
免疫基因序列的变异被认为会影响动物分类群对传染病和寄生虫的抵抗力，进而影响其生存和配偶选择。Toll 样受体（TLR）是脊椎动物先天免疫系统的一个重要基因家族，能够识别所有主要微生物类别的进化保守结构。然而，在雀形目鸟类中 TLR 变异的原因和后果在很大程度上仍未得到探索。我们研究了鸣禽（Melospiza melodia）中的 7 个 TLR 基因，该物种在整个北美洲都有研究。然后，我们检查了该物种分布区域的 2 个部分（N = 27，N = 6）中 4 个未重复的 TLR 基因（TLR1LB、TLR3、TLR4 和 TLR15）的序列，检测选择的证据，并对 TLR 杂合性在生存中的作用进行了初步分析。我们发现了 45 个 SNP：19 个导致氨基酸序列发生变化，其中 2 个可能是有害的。我们没有发现密码子水平间歇性正选择的证据，但在所有 TLR 中都检测到了密码子的纯化选择。与预期相反，我们没有发现 TLR 杂合性与近交系数 f 之间的强烈相关性（估计值 ± 标准误差 [SE] = -0.68 ± 0.37，Radj2 = 0.08，F1,25 = 3.38，P = 0.08）。此外，初步分析显示 TLR 杂合性与生存之间没有关系（β ± SE：0.09 ± 2.00，P = 0.96），这可能是由于样本量小。进一步分析 TLR 中的遗传多样性可能会增进对先天免疫基因多样性对野生种群适应性和持久性的影响的理解。
