Data from: Contemporary evolution of the innate immune receptor gene TLR3 in an isolated vertebrate population

Understanding where genetic variation exists, and how it influences
fitness within populations is important from an evolutionary and
conservation perspective. Signatures of past selection suggest that
pathogen-mediated balancing selection is a key driver of immunogenetic
variation, but studies tracking contemporary evolution are needed to help
resolve the evolutionary forces and mechanism at play. Previous work in a
bottlenecked population of Seychelles warblers (Acrocephalus sechellensis)
show that functional variation has been maintained at the viral-sensing
Toll-like receptor 3 (TLR3) gene, including one non-synonymous SNP,
resulting in two alleles. Here, we characterise evolution at this TLR3
locus over a 25-year period within the original remnant population of the
Seychelles warbler, and in four other derived, populations. Results show a
significant and consistent temporal decline in the frequency of the TLR3C
allele in the original population, and that similar declines in the TLR3C
allele frequency occurred in all the derived populations. Individuals (of
both sexes) with the TLR3CC genotype had lower survival, and males - but
not females - that carry the TLR3C allele had significantly lower lifetime
reproductive success than those with only the TLR3A allele. These results
indicate that positive selection, caused by an as yet unknown agent, is
driving TLR3 evolution in the Seychelles warblers. No evidence of
heterozygote advantage was detected. However, whether the positive
selection observed is part of a longer-term pattern of balancing selection
(through fluctuating selection or rare-allele advantage) cannot be
resolved without tracking the TLR3C allele in the populations over an
extended period of time.

从进化与保护生物学视角出发，明确遗传变异在种群中的分布规律及其对适合度的影响具有重要意义。过往选择特征显示，病原体介导的平衡选择是驱动免疫遗传变异产生的关键因素，但仍需开展当代演化追踪研究，以厘清当前发挥作用的进化力量与作用机制。此前针对塞舌尔莺（Acrocephalus sechellensis）瓶颈种群的研究表明，病毒感知Toll样受体3（TLR3）基因保留了功能变异，其中包含1个非同义单核苷酸多态性（SNP），由此形成两种等位基因。本研究对塞舌尔莺原始残存种群以及另外4个衍生种群的TLR3基因座开展了长达25年的演化特征分析。研究结果显示，原始种群中TLR3C等位基因的频率呈现出显著且稳定的时间下降趋势，且所有衍生种群均观测到了TLR3C等位基因频率的类似下降。携带TLR3CC基因型的个体（无论雌雄）存活率更低；携带TLR3C等位基因的雄性个体（而非雌性），其终身繁殖成功率显著低于仅携带TLR3A等位基因的个体。上述结果表明，由一种尚未明确的媒介引发的正选择，正在驱动塞舌尔莺TLR3基因的演化。本研究未检测到杂合子优势的相关证据。不过，若要确定本次观测到的正选择是否属于长期平衡选择模式（通过波动选择或稀有等位基因优势实现），仍需在更长时间尺度上对种群内TLR3C等位基因的频率变化进行追踪研究。