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 ...多种人类活动已显著加速了生物入侵进程。繁殖体压力（Propagule pressure）指引入个体总数与独立引入事件的数量，该指标易受人类活动影响，同时可能是外来物种在新环境中成功实现分布范围扩张的核心影响因子。本研究以引入分布区美国的捕食性瓢虫七星瓢虫（Coccinella septempunctata）为研究对象，旨在验证其当前的分布格局究竟源于多次历史人为引入事件，还是源自美国境内首批定殖种群的自然扩散扩张。为验证该假说，我们将繁殖体规模、繁殖体数量、具体引入位点及各引入事件发生时间的历史记录，与线粒体DNA（COI）的遗传变异估算结果进行了比对分析。研究结果表明，引入分布区内的遗传多样性与历史记录中的繁殖体规模、繁殖体数量呈正相关，而与距最近引入位点的距离呈负相关……