Data from: A population genetic signature of human releases in an invasive ladybeetle

Biological invasions have been accelerated by a variety of human activities. Propagule pressure, the number of introduced individuals and independent introductions, is likely to be influenced by these human activities and may be an important factor for successful range expansion in new environments. We tested whether the current distribution of the predatory ladybeetle Coccinella septempunctata in the introduced range (USA) is the result of multiple historical human introductions or natural range expansion from the first established populations in the USA. To test this hypothesis, we compared historical records of propagule size, propagule number, specific introduction locations, and the date of each introduction, with estimates of genetic variation in mitochondrial DNA (COI). Our results indicated that genetic diversity in the introduced range was positively correlated with historical records of propagule size and number, and negatively correlated with distance to nearest introduction point, suggesting that multiple human releases were successful. Higher genetic diversity in populations found near introduction points suggest that initial founder effects were limited, but lower genetic diversity found farther from introduction points is likely the result of serial founder effects during secondary range expansion. These results suggest that the current distribution of C. septempunctata in the introduced range is the result of a combination of human releases and short-range expansion from multiple established populations in introduced range.多种人类活动加速了生物入侵进程。繁殖体压力（Propagule pressure）指引入个体数量与独立引入事件的总和，这类指标易受人类活动影响，且可能是物种在新环境中成功实现分布扩张的关键因素。本研究以捕食性天敌七星瓢虫（Coccinella septempunctata）为研究对象，探究其在引入地（美国）的当前分布格局，究竟源于多次历史人为引入事件，还是由美国境内首批定殖种群自然扩散形成。为验证上述假说，本研究将繁殖体规模、繁殖体数量、具体引入位点及各次引入时间的历史记录，与线粒体DNA（COI）的遗传变异估算结果进行对比分析。研究结果显示，引入地种群的遗传多样性与历史记录中的繁殖体规模、数量呈正相关，而与距最近引入位点的距离呈负相关，这表明多次人为释放均取得了成功。引入位点附近种群的遗传多样性更高，说明初始奠基者效应有限；而远离引入位点的种群遗传多样性较低，则大概率是二次分布扩张过程中连续奠基者效应作用的结果。上述结果表明，七星瓢虫在美国引入地的当前分布格局，是人为释放与引入地内多个定殖种群短距离扩散共同作用的产物。