Abstract
Simple SummaryThe whitefly Bemisia tabaci taxon consists of an undefined number of morphologically identical genetic variants of which only a few, including the B, harbor invasive haplotypes. These haplotypes have potential to upsurge and become important pests and plant virus vectors in irrigated agroecosystems worldwide. In the 1980s, unprecedented outbreaks associated with the B variant were reported worldwide, however, the precise origin(s) of the invasive haplotypes has not been determined. In this study, available B. tabaci mitochondrial gene sequences were examined for patterns of conserved single nucleotide changes (SNPs). The whitefly sequence records represented North Africa-Middle Eastern habitats, the proposed B variant center of origin, and distant locales recently invaded by haplotype(s) of the B variant. Unexpectedly, the analysis revealed eight SNPs groups (haplotypes) demonstrating that the genetic architecture of the B mitoype is more complex than previously recognized. Also, the distribution patterns of the eight B haplotypes were tightly linked to well-defined eco-geographic regions, suggesting the different groups have diversified by geographic isolation. Contrary to claims that collectively, the B variant is invasive, only two of the eight haplotypic groups have established in geographical locations outside of their zone of endemism.The Bemisia tabaci cryptic species contains 39 known mitotypes of which the B and Q are best recognized for having established outside their extant endemic range. In the 1980s, previously uncharacterized haplotype(s) of the B mitotype rapidly established in tropical and subtropical locales distant from their presumed center of origin, leading to displacement of several native mitotypes and extreme damage to crops and other vegetation particularly in irrigated agroecosystems. To trace the natural and evolutionary history of the invasive B haplotypes, a phylo-biogeographic study was undertaken. Patterns of single nucleotide polymorphisms (SNPs) and signatures potentially indicative of geographic isolation were investigated using a globally representative mitochondrial cytochrome oxidase I gene (mtCOI) sequence database. Eight haplotype groups within the North Africa-Middle East (NAFME) region were differentiated, NAFME 1–8. The NAFME 1–3 haplotypes were members of the same population that is associated with warm desert climate niches of the Arabian Peninsula and east coastal Africa-Ethiopia. The NAFME 4 and 5 haplotypes are endemic to warm and cold semi-arid niches delimited by the Irano-Turanian floristic region, itself harboring extensive biodiversity. Haplotypes 6 and 7 co-occurred in the Middle East along eastern Mediterranean Sea landmasses, while NAFME 8 was found to be endemic to Cyprus, Turkey, and desert micro-niches throughout Egypt and Israel. Contrary to claims that collectively, the B mitotype is invasive, NAFME 6 and 8 are the only haplotypes to have established in geographical locations outside of their zone of endemism.
Highlights
The whitefly Bemisia tabaci cryptic species group [1,2,3] refers to a mostly polyphagous complex of morphologically cryptic, genetically-distinguishable biological variants distributed worldwide in tropical and sub-tropical regions [4,5,6]
Haplotype North Africa-Middle East (NAFME) 6 had one single nucleotide polymorphisms (SNPs) that resulted in a predicted amino acid change, and the remaining 12 SNPs across the NAFME haplotypes were identified as silent mutations (Table 1)
The mitochondrial cytochrome oxidase (mtCOI) B mitotype-signature SNPs have corroborated the reliability of the mtCOI as a molecular marker and expanded its utility for differentiating haplotypes at a finer scale
Summary
The whitefly Bemisia tabaci cryptic (or sibling) species group [1,2,3] refers to a mostly polyphagous complex of morphologically cryptic, genetically-distinguishable biological variants distributed worldwide in tropical and sub-tropical regions [4,5,6]. Seven major phylogeographic clades have been resolved based on phylogenetic analysis of the partial mitochondrial cytochrome oxidase (mtCOI) gene sequence [1,7], collectively comprising 39 genetically divergent mitotypes. Five of these major phylogeographic clades have been corroborated in an analysis of 2184 single copy orthologous nuclear genes [2]. During the mid-1970s, unprecedented outbreaks and crop damage have been reported in Israel and Egypt, while another major outbreak occurred in Israel in 1988 [9]. Among the mitotypes of historical importance are the well-known B and Q mitotypes [1,15,16,17,18,19,20,21], the A mitotype endemic to the American tropics and Caribbean Basin [9,22], the Asia I and II in the Indian subcontinent [23,24,25,26], and sub-Saharan Africa mitotypes [27,28,29]
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