Biogéosciences, UMR CNRS 6282, Université de Bourgogne 6 Boulevard Gabriel, 21000, Dijon, France ; Laboratoire LBBE, UMR CNRS 5558, Université Claude Bernard Lyon 1 bâtiment Mendel, 43 boulevard du 11 novembre 1918, 69622, Villeurbanne Cedex, France.
Department of Zoology, University of Venda Private Bag X5050, Thohoyandou, 0950, South Africa ; Department of Integrative Biology and Evolution, Konrad-Lorenz-Institute of Ethology, University of Veterinarian Medicine Vienna Savoyenstr. 1a, A-1160, Vienna, Austria.
Ecol Evol. 2015 Apr;5(8):1639-52. doi: 10.1002/ece3.1452. Epub 2015 Mar 23.
Small and isolated populations usually exhibit low levels of genetic variability, and thus, they are expected to have a lower capacity to adapt to changes in environmental conditions, such as exposure to pathogens and parasites. Comparing the genetic variability of selectively neutral versus functional loci allows one to assess the evolutionary history of populations and their future evolutionary potential. The genes of the major histocompatibility complex (MHC) control immune recognition of parasites, and their unusually high diversity is genes which is likely driven by parasite-mediated balancing selection. Here, we examined diversity and differentiation of neutral microsatellite loci and functional MHC class I genes in house sparrows (Passer domesticus), living in six insular and six mainland populations, and we aimed to determine whether their diversity or differentiation correlates with the diversity and the prevalence of infection of hemosporidian parasites. We found that island bird populations tended to have lower neutral genetic variability, whereas MHC variability gene was similar between island and mainland populations. Similarly, island populations tended to show greater genetic differentiation than mainland populations, especially at microsatellite markers. The maintenance of MHC genetic diversity and its less marked structure in the island populations could be attributed to balancing-selection. The greater MHC differentiation among populations was negatively correlated with similarity in blood parasites (prevalence and diversity of parasite strains) between populations. Even at low prevalence and small geographical scale, haemosporidian parasites might contribute to structure the variability of immune genes among populations of hosts.
小而孤立的种群通常表现出较低的遗传变异性，因此，它们预计适应环境条件变化（如暴露于病原体和寄生虫）的能力较低。比较选择性中性和功能基因座的遗传变异性可以评估种群的进化历史及其未来的进化潜力。主要组织相容性复合体 (MHC) 的基因控制对寄生虫的免疫识别，其非同寻常的高度多样性是由寄生虫介导的平衡选择驱动的。在这里，我们研究了生活在六个岛屿和六个大陆种群中的家麻雀（Passer domesticus）中性微卫星基因座和功能 MHC 类 I 基因的多样性和分化，并旨在确定它们的多样性或分化是否与感染血孢子虫寄生虫的多样性和流行率相关。我们发现，岛屿鸟类种群的中性遗传变异性往往较低，而 MHC 变异性基因在岛屿和大陆种群之间相似。同样，岛屿种群的遗传分化往往大于大陆种群，尤其是在微卫星标记上。MHC 遗传多样性的维持及其在岛屿种群中的结构不那么明显，可能归因于平衡选择。种群之间 MHC 的更大分化与种群之间血液寄生虫（寄生虫株的流行率和多样性）的相似性呈负相关。即使在低流行率和小地理尺度下，血孢子虫寄生虫也可能有助于构建宿主种群中免疫基因的变异性。
