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Species-complex diversification and host-plant associations in Bemisia tabaci: A plant-defence, detoxification perspective revealed by RNA-Seq analyses.

ABSTRACT: Insect-plant associations and their role in diversification are mostly studied in specialists. Here, we aimed to identify macroevolution patterns in the relationships between generalists and their host plants that have the potential to promote diversification. We focused on the Bemisia tabaci species complex containing more than 35 cryptic species. Mechanisms for explaining this impressive diversification have focused so far on allopatric forces that assume a common, broad, host range. We conducted a literature survey which indicated that species in the complex differ in their host range, with only few showing a truly broad one. We then selected six species, representing different phylogenetic groups and documented host ranges. We tested whether differences in the species expression profiles of detoxification genes are shaped more by their phylogenetic relationships or by their ability to successfully utilize multiple hosts, including novel ones. Performance assays divided the six species into two groups of three, one showing higher performance on various hosts than the other (the lower performance group). The same grouping pattern appeared when the species were clustered according to their expression profiles. Only species placed in the lower performance group showed a tendency to lower the expression of multiple genes. Taken together, these findings bring evidence for the existence of a common detoxification "machinery," shared between species that can perform well on multiple hosts. We raise the possibility that this "machinery" might have played a passive role in the diversification of the complex, by allowing successful migration to new/novel environments, leading, in some cases, to fragmentation and speciation.

SUBMITTER: Malka O

PROVIDER: S-EPMC6334513 | biostudies-literature | 2018 Nov

REPOSITORIES: biostudies-literature

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Species-complex diversification and host-plant associations in Bemisia tabaci: A plant-defence, detoxification perspective revealed by RNA-Seq analyses.

Malka Osnat O Santos-Garcia Diego D Feldmesser Ester E Sharon Elad E Krause-Sakate Renate R Delatte Hélène H van Brunschot Sharon S Patel Mitulkumar M Visendi Paul P Mugerwa Habibu H Seal Susan S Colvin John J Morin Shai S

Molecular ecology 20181010 21

Insect-plant associations and their role in diversification are mostly studied in specialists. Here, we aimed to identify macroevolution patterns in the relationships between generalists and their host plants that have the potential to promote diversification. We focused on the Bemisia tabaci species complex containing more than 35 cryptic species. Mechanisms for explaining this impressive diversification have focused so far on allopatric forces that assume a common, broad, host range. We conduc ...[more]

PMID: 30222226

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Project description:BackgroundHumans and insect herbivores are competing for the same food crops and have been for thousands of years. Despite considerable advances in crop pest management, losses due to insects remain considerable. The global homogenisation of agriculture has supported the range expansion of numerous insect pests and has been driven in part by human-assisted dispersal supported through rapid global trade and low-cost air passenger transport. One of these pests, is the whitefly, Bemisia tabaci, a cryptic species complex that contains some of the world's most damaging pests of agriculture. The complex shows considerable genetic diversity and strong phylogeographic relationships. One consequence of the considerable impact that members of the B. tabaci complex have on agriculture, is the view that human activity, particularly in relation to agricultural practices, such as use of insecticides, has driven the diversification found within the species complex. This has been particularly so in the case of two members of the complex, Middle East-Asia Minor 1 (MEAM1) and Mediterranean (MED), which have become globally distributed invasive species. An alternative hypothesis is that diversification is due to paleogeographic and paleoclimatological changes.ResultsThe idea that human activity is driving speciation within the B. tabaci complex has never been tested, but the increased interest in fossil whiteflies and the growth in molecular data have enabled us to apply a relaxed molecular clock and so estimate divergence dates for the major lineages within the B. tabaci species complex. The divergence estimates do not support the view that human activity has been a major driver of diversification.ConclusionsOur analysis suggests that the major lineages within the complex arose approximately 60-30 mya and the highly invasive MED and MEAM1 split from the rest of the species complex around 12 mya well before the evolution of Homo sapiens and agriculture. Furthermore, the divergence dates coincide with a period of global diversification that occurred broadly across the plant and animal kingdoms and was most likely associated with major climatic and tectonic events.

Project description:The whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), and the viruses it transmits, are a major constraint to vegetable crops, worldwide. Although the whitefly is usually controlled using chemical pesticides, biological control agents constitute an important component in integrated pest management programs. One of these agents is the wasp Eretmocerus mundus (Mercet) (Hymenoptera: Aphelinidae). E. mundus lays its egg on the leaf underneath the pupa of B. tabaci. First instars of the wasp hatch and penetrate the whitefly larvae. Initiation of parasitization induces the host to form a cellular capsule around the parasitoid. Around this capsule, epidermal cells multiply and thick layers of cuticle are deposited. The physiological and molecular processes underlying B. tabaci-E. mundus interactions have not been investigated so far. We have used a cDNA microarray containing 6,000 expressed sequence tags (ESTs) from the whitefly genome to study the parasitoid-whitefly interaction. We compared RNA samples collected across two time points of the parasitization process: when the parasitoid first instar started the penetration process and once it had fully penetrated the host. The results clearly indicated that genes known to be part of the defense pathways described in other insects are also involved in the response of B. tabaci to parasitization by E. mundus. Some of the responses observed included the repression of a serine protease inhibitor (serpin) and the induction of a melanization cascade. A second set of genes that strongly responded to parasitization included bacterial genes encoded by whitefly symbionts. Quantitative real-time PCR and FISH analyses showed that proliferation of Rickettsia, a facultative secondary symbiont, was strongly induced following the initiation of the parasitization process, a result that supported previous reports suggesting that endosymbionts may be involved in the insect host resistance to various environmental stresses. This is the first study examining the transcriptional response of a hemipteran insect to the attack of a biological control agent (Hymenopterous parasitoid), using a new genomic approach developed for this insect pest. The defense response in B. tabaci seems to resemble that of model organisms such as Drosophila melanogaster. Moreover, endosymbionts of B. tabaci seem to play a role in the response to parasitization, and this is supported by previously published results from aphids. Keywords: time course

Dataset Information

Species-complex diversification and host-plant associations in Bemisia tabaci: A plant-defence, detoxification perspective revealed by RNA-Seq analyses.

Publications

Species-complex diversification and host-plant associations in Bemisia tabaci: A plant-defence, detoxification perspective revealed by RNA-Seq analyses.

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