Department of Environmental Science, Policy and Management, University of California-Berkeley, Berkeley, CA, USA.
Department of Biological Sciences, Towson University, Towson, MD, USA.
Infect Genet Evol. 2019 Sep;73:197-204. doi: 10.1016/j.meegid.2019.04.032. Epub 2019 Apr 30.
Major histocompatibility complex (MHC) genes code for membrane-embedded proteins that are involved in parasite/pathogen recognition. The link between the MHC and immunity makes these genes important genetic markers to evaluate in systems where infectious disease is associated with population declines. As human impacts on wildlife populations continue to increase, it is also essential to evaluate the role of MHC and immunity in the context of anthropogenic change. Amphibians are an ideal model to test the role of the MHC in infectious disease resistance, as parasites and anthropogenic disturbances currently threaten populations worldwide. We characterized the diversity of MHC class IIβ peptide binding region alleles, 13 microsatellite loci, and population-level trematode resistance in 14 populations of wood frogs (Lithobates sylvaticus) in northwestern Pennsylvania with varying geographic distances to agriculture. To assess local adaptation in the MHC IIβ, we compared genetic differentiation of MHC IIβ and microsatellite markers (F). We also tested for an effect of isolation by distance on genetic differentiation of MHC IIβ and microsatellite markers. In addition, we evaluated whether population-level MHC IIβ diversity and common allele frequencies correlate with distance to agriculture and trematode resistance. We found no evidence for genetic structure based on microsatellite analysis nor an effect of isolation by distance on neutral and immunogenetic markers. However, we did detect structure based on the MHC IIβ locus, suggesting that it is under local selection. The MHC IIβ allele Lisy-DAB*1 was more common in populations living near agricultural sites. Populations with higher MHC IIβ diversity showed increased resistance to trematodes. Our results suggest that wood frog populations experience immunogenetic differences at a small scale. In addition, agriculture may disturb natural associations between hosts and parasites through its influence on immunocompetence, underscoring the importance of examining the effects of environmental context on host-parasite interactions.
主要组织相容性复合体 (MHC) 基因编码参与寄生虫/病原体识别的膜嵌入蛋白。MHC 与免疫之间的联系使这些基因成为评估与传染病相关的种群下降的重要遗传标记。随着人类对野生动物种群的影响继续增加，评估 MHC 和免疫在人为变化背景下的作用也至关重要。两栖动物是测试 MHC 在传染病抵抗力中的作用的理想模型，因为寄生虫和人为干扰目前威胁着全球的种群。我们描述了宾夕法尼亚州西北部 14 个林蛙 (Lithobates sylvaticus) 种群的 MHC 类 IIβ 肽结合区等位基因、13 个微卫星位点和种群水平吸虫抗性的多样性，这些种群与农业的地理距离不同。为了评估 MHC IIβ 的局部适应，我们比较了 MHC IIβ 和微卫星标记 (F) 的遗传分化。我们还测试了隔离距离对 MHC IIβ 和微卫星标记遗传分化的影响。此外，我们评估了种群水平的 MHC IIβ 多样性和常见等位基因频率是否与距离农业和吸虫抗性相关。我们没有发现基于微卫星分析的遗传结构的证据，也没有发现隔离距离对中性和免疫遗传标记的影响。然而，我们确实在 MHC IIβ 基因座上检测到了结构，表明它受到局部选择的影响。MHC IIβ 等位基因 Lisy-DAB*1 在靠近农业地点的种群中更为常见。具有更高 MHC IIβ 多样性的种群对吸虫的抵抗力更高。我们的研究结果表明，林蛙种群在小范围内经历免疫遗传差异。此外，农业可能通过影响免疫能力来干扰宿主与寄生虫之间的自然联系，突出了研究环境背景对宿主-寄生虫相互作用的影响的重要性。
