Data from: Colonization of the Mediterranean Basin by the vector biting midge species Culicoides imicola: an old story

Understanding the demographic history and genetic make-up of colonizing species is critical for inferring population sources and colonization routes. This is of main interest for designing accurate control measures in areas newly colonized by vector species of economically important pathogens. The biting midge Culicoides imicola is a major vector of orbiviruses to livestock. Historically, the distribution of this species was limited to the Afrotropical region. Entomological surveys first revealed the presence of C. imicola in the south of the Mediterranean basin by the 1970s. Following recurrent reports of massive bluetongue outbreaks since the 1990s, the presence of the species was confirmed in northern areas. In this study, we addressed the chronology and processes of C. imicola colonization in the Mediterranean basin. We characterized the genetic structure of its populations across Mediterranean and African regions using both mitochondrial and nuclear markers, and combined phylogeographical analyses with population genetics and approximate Bayesian computation. We found a west/east genetic differentiation between populations, occurring both within Africa and within the Mediterranean basin. We demonstrated that three of these groups had experienced demographic expansions in the Pleistocene, probably because of climate changes during this period. Finally, we showed that C. imicola could have colonized the Mediterranean basin in the Late Pleistocene or Early Holocene through a single event of introduction; however, we cannot exclude the hypothesis involving two routes of colonization. Thus, the recent bluetongue outbreaks are not linked to C. imicola colonization event, but rather to biological changes in the vector or the virus.

解析入侵物种的种群历史与遗传组成，对于推断其种群来源及入侵路径至关重要，这对于经济重要性病原体媒介物种新近入侵的区域制定精准防控策略具有核心意义。吸血蠓伊莫库蠓（Culicoides imicola）是家畜环状病毒（orbivirus）的主要传播媒介。历史上，该物种的分布范围仅局限于非洲热带区。1970年代，昆虫学调查首次在地中海盆地南部发现伊莫库蠓的踪迹。自1990年代以来，随着大规模蓝舌病暴发的报道持续涌现，研究人员证实该物种已扩散至地中海北部区域。本研究聚焦伊莫库蠓在地中海盆地的入侵时间与扩散过程：研究人员通过线粒体及核分子标记，对地中海与非洲区域的伊莫库蠓种群遗传结构进行了表征，并将系统地理学（phylogeographical）分析与种群遗传学、近似贝叶斯计算（approximate Bayesian computation）相结合。研究发现，无论是非洲境内还是地中海盆地内部，伊莫库蠓种群均存在东西向的遗传分化。本研究证实，其中三个种群支系在更新世（Pleistocene）时期经历了种群数量扩张，这一事件大概率与该时期的气候变化相关。最终，本研究表明，伊莫库蠓可能在晚更新世或全新世早期通过单次入侵事件扩散至地中海盆地；但研究无法排除通过两条独立入侵路径完成扩散的假说。由此可见，近年暴发的蓝舌病疫情与伊莫库蠓的入侵事件并无关联，而是与媒介昆虫本身或病毒的生物学特性变化有关。