Cryptic Diversity within the Major Trypanosomiasis Vector Glossina fuscipes Revealed by Molecular Markers

BackgroundThe tsetse fly Glossina fuscipes s.l. is responsible for the transmission of approximately 90% of cases of human African trypanosomiasis (HAT) or sleeping sickness. Three G. fuscipes subspecies have been described, primarily based upon subtle differences in the morphology of their genitalia. Here we describe a study conducted across the range of this important vector to determine whether molecular evidence generated from nuclear DNA (microsatellites and gene sequence information), mitochondrial DNA and symbiont DNA support the existence of these taxa as discrete taxonomic units. Principal FindingsThe nuclear ribosomal Internal transcribed spacer 1 (ITS1) provided support for the three subspecies. However nuclear and mitochondrial sequence data did not support the monophyly of the morphological subspecies G. f. fuscipes or G. f. quanzensis. Instead, the most strongly supported monophyletic group was comprised of flies sampled from Ethiopia. Maternally inherited loci (mtDNA and symbiont) also suggested monophyly of a group from Lake Victoria basin and Tanzania, but this group was not supported by nuclear loci, suggesting different histories of these markers. Microsatellite data confirmed strong structuring across the range of G. fuscipes s.l., and was useful for deriving the interrelationship of closely related populations. Conclusion/SignificanceWe propose that the morphological classification alone is not used to classify populations of G. fuscipes for control purposes. The Ethiopian population, which is scheduled to be the target of a sterile insect release (SIT) programme, was notably discrete. From a programmatic perspective this may be both positive, given that it may reflect limited migration into the area or negative if the high levels of differentiation are also reflected in reproductive isolation between this population and the flies to be used in the release programme.研究背景 须舌蝇复合种（Glossina fuscipes s.l.）约造成90%的人类非洲锥虫病（human African trypanosomiasis, HAT，又称昏睡病）感染病例。目前已记述该复合种下存在3个亚种，分类依据主要为其生殖器形态的细微差异。本研究覆盖该重要媒介昆虫的分布范围，旨在通过核DNA（微卫星与基因序列信息）、线粒体DNA及共生菌DNA获取的分子证据，验证这些分类群是否为独立的分类单元。 主要研究结果 核核糖体内部转录间隔区1（Internal transcribed spacer 1, ITS1）的分析结果支持这3个亚种的存在。但核与线粒体序列数据并不支持形态学亚种须舌蝇指名亚种（G. f. fuscipes）或宽扎亚种（G. f. quanzensis）为单系群。与之相反，支持度最高的单系群由埃塞俄比亚采集的舌蝇样本组成。母系遗传位点（线粒体DNA与共生菌DNA）同样显示维多利亚湖流域与坦桑尼亚的样本构成单系群，但核位点并不支持这一聚类，表明不同分子标记具有各自的演化历史。微卫星数据证实须舌蝇复合种种群在其分布范围内存在显著的遗传结构，且可用于解析亲缘关系较近的种群间的演化关系。 结论与意义 我们建议在开展须舌蝇复合种种群防治工作时，不应仅依据形态学特征进行种群分类。原本计划作为不育昆虫释放（Sterile Insect Release, SIT）项目防治靶标的埃塞俄比亚种群，其与其他种群的遗传分化程度极高，独立性显著。从项目实施角度而言，这一结果兼具利弊：一方面，种群间有限的基因流提示该区域外来种群入侵风险较低，这是有利因素；另一方面，若该种群与释放用蝇类间存在生殖隔离（由高水平遗传分化所体现），则会对防治效果产生不利影响。