Data from: Estimation of the dispersal of a major pest of maize by cline analysis of a temporary contact zone between two invasive outbreaks

Dispersal is a key factor in invasion, and in the persistence and evolution of species. Despite the importance of estimates of dispersal distance, dispersal measurement remains a real methodological challenge. In this study, we characterized dispersal by exploiting a specific case of biological invasion, in which multiple introductions in disconnected areas lead to secondary contact between two differentiated expanding outbreaks. By applying cline theory to this ecological setting, we estimated σ, the standard deviation of the parent-offspring distance distribution, of the western corn rootworm, Diabrotica virgifera virgifera, one of the most destructive pests of maize. This species is currently invading Europe, and the two largest invasive outbreaks, in Northern Italy and Central Europe, have recently formed a secondary contact zone in Northern Italy. We identified vanishing clines at 12 microsatellite loci throughout the contact zone. By analyzing both the rate of change of cline slope and the spatial variation of linkage disequilibrium at these markers, we obtained two σ estimates of about 20 km.generation−1/2. Simulations indicated that these estimates were robust to changes in dispersal kernels and differences in population density between the two outbreaks, despite a systematic weak bias. These estimates are consistent with the results of direct methods for measuring dispersal applied to the same species. We conclude that secondary contact resulting from multiple introductions is very useful for the inference of dispersal parameters and should be more widely used in other species.扩散是生物入侵、物种存续与演化的关键驱动因素。尽管扩散距离估算具有重要意义，但扩散测量始终是一项颇具挑战性的方法学难题。在本研究中，我们借助一个特定的生物入侵案例开展扩散特征表征：该案例中，孤立生境中的多次引种事件致使两个分化后的扩张暴发种群形成二次接触。我们将渐变群（cline）理论应用于这一生态场景，估算了西方玉米根萤叶甲（Diabrotica virgifera virgifera）的亲代-子代距离分布标准差σ——该物种是危害玉米最严重的害虫之一，目前正在欧洲扩散入侵。其两大入侵暴发种群分别位于意大利北部与中欧，近期在意大利北部形成了二次接触带。我们在该接触带内的12个微卫星位点（microsatellite loci）中检测到了渐消渐变群（vanishing clines）。通过分析渐变群斜率的变化速率与这些标记位点的连锁不平衡（linkage disequilibrium）空间变异，我们得到了两个约为20 km·generation⁻¹/²的σ估算值。模拟实验结果表明，尽管存在系统性弱偏倚，但这些估算值对扩散核（dispersal kernels）的变化与两个暴发种群间的种群密度差异具有稳健性。上述估算结果与针对同一物种采用直接扩散测量法得到的研究结果一致。我们由此得出结论：多次引种所引发的二次接触可有效用于扩散参数的推断，该方法应在更多物种中得到更广泛的应用。