Data from: Urbanization as a facilitator of gene flow in a human health pest

Urban fragmentation can reduce gene flow that isolates populations, reduces genetic diversity and increases population differentiation, all of which have negative conservation implications. Alternatively, gene flow may actually be increased among urban areas consistent with an urban facilitation model. In fact, urban adapter pests are able to thrive in the urban environment and may be experiencing human-mediated transport. Here, we used social network theory with a population genetic approach to investigate the impact of urbanization on genetic connectivity in the Western black widow spider, as an urban pest model of human health concern. We collected genomewide SNP variation from mitochondrial and nuclear ddRAD sequence datasets from 210 individuals sampled from 11 urban and 10 non-urban locales across its distribution of the Western U.S. From urban and non-urban contrasts of population, phylogenetic, and network analyses, urban locales have higher within-population genetic diversity, lower between-population genetic differentiation, and higher estimates of genetic connectivity. Social network analyses show that urban locales not only have more connections, but can act as hubs that drive connectivity among non-urban locales, which show signatures of historical isolation. These results are consistent with an urban facilitation model of gene flow, and demonstrate the importance of sampling multiple cities and markers to identify the role that urbanization has had on larger spatial scales. As the urban landscape continues to grow, this approach will help determine what factors influence the spread and adaptation of pests, like the venomous black widow spider, in building policies for human and biodiversity health.

城市生境破碎化会降低基因流，进而引发种群隔离、遗传多样性衰减与种群分化加剧，上述效应均会对物种保护产生负面影响。
与之相对，城市区域间的基因流反而可能增强，这契合“城市促进模型”（urban facilitation model）。事实上，城市适应性害虫可在城市环境中繁盛繁衍，且可能通过人类活动介导实现跨区域扩散。
本研究整合社交网络理论与种群遗传学研究范式，以一类关乎人类健康的城市害虫模型物种——西部黑寡妇蜘蛛（Western black widow spider）为研究对象，探究城市化对其遗传连通性的影响。
我们从美国西部该物种的分布范围内，选取11个城市样点与10个非城市样点，共采集210只个体的基因组范围单核苷酸多态性（Single Nucleotide Polymorphism, SNP）变异数据，数据来源于线粒体与核基因组双酶切限制性位点关联DNA测序（double digest restriction-site associated DNA sequencing, ddRAD）数据集。
通过对城市与非城市样点开展种群、系统发育及网络分析对比，结果显示城市样点的种群内遗传多样性更高、种群间遗传分化更低，且遗传连通性的估计值更高。
社交网络分析结果表明，城市样点不仅具备更多的连通节点，还可作为枢纽驱动非城市样点间的遗传连通性；而非城市样点则呈现出历史隔离的特征。
上述结果与基因流的城市促进模型相符，同时也证实了通过多城市、多标记物采样，以明确城市化在更大空间尺度上所发挥作用的必要性。
随着城市景观持续扩张，本研究方法将有助于明确在制定人类健康与生物多样性保护政策时，哪些因素会影响诸如有毒黑寡妇蜘蛛这类害虫的扩散与适应性演化。