Habitat fragmentation is a major cause of biodiversity loss, responsible for an alteration of intraspecific patterns of neutral genetic diversity and structure. Although neutral genetic variation can be informative for demographic inferences, it may be a poor predictor of adaptive genetic diversity and thus of the consequences of habitat fragmentation on selective evolutionary processes. In this context, we contrasted patterns of genetic diversity and structure of neutral loci (microsatellites) and immune genes (i.e., toll-like receptors) in an understorey bird species, the wedge-billed woodcreeper Glyphorynchus spirurus . The objectives were (1) to investigate forest fragmentation effects on population genetic diversity, (2) to disentangle the relative role of demography (genetic drift and migration) and selection, and (3) to assess whether immunogenetic patterns could be associated with variation of ectoparasite (i.e., ticks) pressures. Our results revealed an erosion of neutral genetic diversity and a substantial genetic differentiation among fragmented populations, resulting from a decrease in landscape connectivity and leading to the divergence of distinct genetic pools at a small spatial scale. Patterns of genetic diversity observed for TLR4 and TLR5 were concordant with neutral genetic patterns, whereas those observed for TLR3 and TLR21 were discordant. This result underlines that the dominant evolutionary force shaping immunogenetic diversity (genetic drift vs. selection) may be different depending on loci considered. Finally, tick prevalence was higher in fragmented environments. We discussed the hypothesis that pathogen selective pressures may contribute to maintain adaptive genetic diversity despite the negative demographic effect of habitat fragmentation on neutral genetic diversity.

中文翻译：

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栖息地破碎化对热带鸟类中性和免疫基因变异的影响不同


栖息地破碎化是生物多样性丧失的主要原因，导致中性遗传多样性和结构的种内模式发生改变。尽管中性遗传变异可以为人口统计推断提供信息，但它可能不能很好地预测适应性遗传多样性，从而预测栖息地破碎化对选择性进化过程的影响。在这种情况下，我们对比了一种林下鸟类——楔形嘴爬山鸟 Glyphorynchus spirurus 的遗传多样性模式、中性基因座（微卫星）和免疫基因（即 Toll 样受体）的结构。目标是（1）研究森林破碎化对种群遗传多样性的影响，（2）理清人口统计学（遗传漂变和迁移）和选择的相对作用，以及（3）评估免疫遗传模式是否可能与种群遗传多样性的变化相关。外寄生虫（即蜱）压力。我们的研究结果揭示了中性遗传多样性的侵蚀以及分散种群之间的显着遗传分化，这是由于景观连通性下降造成的，并导致小空间尺度上不同遗传库的分歧。观察到的 TLR4 和 TLR5 遗传多样性模式与中性遗传模式一致，而观察到的 TLR3 和 TLR21 遗传多样性模式则不一致。这一结果强调，塑造免疫遗传多样性（遗传漂变与选择）的主导进化力量可能因所考虑的基因座而异。最后，在分散的环境中，蜱虫的流行率更高。 我们讨论了这样的假设：尽管栖息地破碎化对中性遗传多样性产生了负面的人口统计影响，但病原体选择压力可能有助于维持适应性遗传多样性。