Natural Resources Institute, University of Greenwich, Central Avenue, Chatham Maritime, Kent, UK.
Department of Entomology, University of Georgia, Griffin, Georgia, USA.
Insect Sci. 2021 Dec;28(6):1553-1566. doi: 10.1111/1744-7917.12881. Epub 2020 Nov 30.
In sub-Saharan Africa cassava growing areas, two members of the Bemisia tabaci species complex termed sub-Saharan Africa 1 (SSA1) and SSA2 have been reported as the prevalent whiteflies associated with the spread of viruses that cause cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) pandemics. At the peak of CMD pandemic in the late 1990s, SSA2 was the prevalent whitefly, although its numbers have diminished over the last two decades with the resurgence of SSA1 whiteflies. Three SSA1 subgroups (SG1 to SG3) are the predominant whiteflies in East Africa and vary in distribution and biological properties. Mating compatibility between SSA1 subgroups and SSA2 whiteflies was reported as the possible driver for the resurgence of SSA1 whiteflies. In this study, a combination of both phylogenomic methods and reciprocal crossing experiments were applied to determine species status of SSA1 subgroups and SSA2 whitefly populations. Phylogenomic analyses conducted with 26 548 205 bp whole genome single nucleotide polymorphisms (SNPs) and the full mitogenomes clustered SSA1 subgroups together and separate from SSA2 species. Mating incompatibility between SSA1 subgroups and SSA2 further demonstrated their distinctiveness from each other. Phylogenomic analyses conducted with SNPs and mitogenomes also revealed different genetic relationships among SSA1 subgroups. The former clustered SSA1-SG1 and SSA1-SG2 together but separate from SSA1-SG3, while the latter clustered SSA1-SG2 and SSA1-SG3 together but separate from SSA1-SG1. Mating compatibility was observed between SSA1-SG1 and SSA1-SG2, while incompatibility occurred between SSA1-SG1 and SSA1-SG3, and SSA1-SG2 and SSA1-SG3. Mating results among SSA1 subgroups were coherent with phylogenomics results based on SNPs but not the full mitogenomes. Furthermore, this study revealed that the secondary endosymbiont-Wolbachia-did not mediate reproductive success in the crossing assays carried out. Overall, using genome wide SNPs together with reciprocal crossings assays, this study established accurate genetic relationships among cassava-colonizing populations, illustrating that SSA1 and SSA2 are distinct species while at least two species occur within SSA1 species.
在撒哈拉以南非洲的木薯种植区，已报道两种称为撒哈拉以南非洲 1 型（SSA1）和 SSA2 的烟粉虱种群为与传播引起木薯花叶病（CMD）和木薯褐条病（CBSD）大流行的病毒相关的主要粉虱。在 20 世纪 90 年代末期 CMD 大流行高峰期，SSA2 是主要的粉虱，但在过去二十年中，随着 SSA1 粉虱的重新出现，其数量有所减少。三个 SSA1 亚型（SG1 到 SG3）是东非的主要粉虱，其分布和生物学特性有所不同。据报道，SSA1 亚型和 SSA2 粉虱之间的交配相容性是 SSA1 粉虱重新出现的可能驱动因素。在这项研究中，综合使用系统基因组学方法和正反交实验来确定 SSA1 亚型和 SSA2 粉虱种群的物种地位。使用 26548205bp 全基因组单核苷酸多态性（SNP）和完整线粒体基因组进行的系统基因组分析将 SSA1 亚型聚在一起，并与 SSA2 物种分开。SSA1 亚型之间的交配不兼容性进一步证明了它们彼此之间的独特性。使用 SNP 和线粒体基因组进行的系统基因组分析还揭示了 SSA1 亚型之间不同的遗传关系。前者将 SSA1-SG1 和 SSA1-SG2 聚在一起，但与 SSA1-SG3 分开，而后者将 SSA1-SG2 和 SSA1-SG3 聚在一起，但与 SSA1-SG1 分开。SSA1-SG1 和 SSA1-SG2 之间观察到交配相容性，而 SSA1-SG1 和 SSA1-SG3 之间以及 SSA1-SG2 和 SSA1-SG3 之间则存在交配不相容性。SSA1 亚型之间的交配结果与基于 SNP 的系统基因组学结果一致，但与完整线粒体基因组的结果不一致。此外，这项研究表明，在进行的交叉实验中，次级共生菌-沃尔巴克氏体并没有介导繁殖成功。总的来说，使用全基因组 SNP 结合正反交实验，本研究建立了木薯定殖种群之间准确的遗传关系，表明 SSA1 和 SSA2 是不同的物种，而 SSA1 种内至少存在两个物种。
