Population Biology and Conservation Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen18D, SE-752 36 Uppsala, Sweden.
Mol Ecol. 2011 Apr;20(8):1582-600. doi: 10.1111/j.1365-294X.2011.05025.x. Epub 2011 Feb 17.
One of the main questions in evolutionary and conservation biology is how geographical and environmental features of the landscape shape neutral and adaptive genetic variation in natural populations. The identification of genomic polymorphisms that account for adaptive variation can aid in finding candidate loci for local adaptation. Consequently, a comparison of spatial patterns in neutral markers and loci under selection may help disentangle the effects of gene flow, genetic drift and selection at the landscape scale. Many amphibians breed in wetlands, which differ in environmental conditions and in the degree of isolation, enhancing the potential for local adaptation. We used microsatellite markers to measure genetic differentiation among 17 local populations of Rana arvalis breeding in a network of wetlands. We found that locus RC08604 deviated from neutral expectations, suggesting that it is a good candidate for directional selection. We used a genetic network analysis to show that the allele distribution in this locus is correlated with habitat characteristics, whereas this was not the case at neutral markers that displayed a different allele distribution and population network in the study area. The graph approach illustrated the genomic heterogeneity (neutral loci vs. the candidate locus for directional selection) of gene exchange and genetic divergence among populations under directional selection. Limited gene flow between wetlands was only observed at the candidate genomic region under directional selection. RC08604 is partially located inside an up-regulated thyroid-hormone receptor (TRβ) gene coordinating the expression of other genes during metamorphosis and appears to be linked with variation in larval life-history traits found among R. arvalis populations. We suggest that directional selection on genes coding larval life-history traits is strong enough to maintain the divergence in these genomic regions, reducing the effective recombination of locally adapted alleles but not in other regions of the genome. Integrating this knowledge into conservation plans at the landscape scale will improve the design of management strategies to preserve adaptive genetic diversity in wetland networks.
进化和保护生物学的主要问题之一是，景观的地理和环境特征如何塑造自然种群中的中性和适应性遗传变异。确定解释适应性变异的基因组多态性可以帮助找到适应局部的候选基因座。因此，比较中性标记和选择下的基因座的空间模式可以帮助理清基因流、遗传漂变和景观尺度选择的影响。许多两栖动物在湿地中繁殖，湿地在环境条件和隔离程度上存在差异，增强了适应局部环境的潜力。我们使用微卫星标记来衡量在一个湿地网络中繁殖的 17 个 Rana arvalis 本地种群之间的遗传分化。我们发现，RC08604 基因座偏离中性预期，表明它是定向选择的良好候选基因座。我们使用遗传网络分析表明，该基因座的等位基因分布与栖息地特征相关，而在中性标记中则不是这样，中性标记在研究区域中显示出不同的等位基因分布和种群网络。图形方法说明了在定向选择下基因交换和种群间遗传分化的基因组异质性（中性基因座与定向选择的候选基因座）。只有在候选基因座中观察到受定向选择影响的基因座内的有限基因流。RC08604 部分位于上调的甲状腺激素受体（TRβ）基因内，该基因在变态期间协调其他基因的表达，并且似乎与 R. arvalis 种群中发现的幼虫生活史特征的变异有关。我们认为，编码幼虫生活史特征的基因的定向选择足够强大，可以维持这些基因组区域的分化，减少对本地适应等位基因的有效重组，但不能减少基因组的其他区域。将这一知识纳入景观尺度的保护计划将有助于改进管理策略的设计，以保护湿地网络中的适应性遗传多样性。
