Abstract
BackgroundDivergent selection has been shown to promote speciation in many taxa and especially in phytophagous insects. In the Ostrinia species complex, the European corn borer (ECB) and adzuki bean borer (ABB) are two sibling species specialized to different host plants. The first is a well-known maize pest, whereas the second is a polyphagous species associated with various dicotyledons. Their specialization to host plants is driven by morphological, behavioral and physiological adaptations. In particular, previous studies have shown that ECB and ABB display marked behavior with regard to plant choice during oviposition, involving specific preference and avoidance mechanisms. In this study, our goal was to identify the mechanisms underlying this host-plant specialization in adult females through an analysis of their gene expression. We assembled and annotated a de novo reference transcriptome and measured differences in gene expression between ECB and ABB females, and between environments. We related differentially expressed genes to host preference behavior, and highlighted the functional categories involved. We also conducted a specific analysis of chemosensory genes, which are considered to be good candidates for host recognition before oviposition.ResultsWe recorded more differentially expressed genes in ECB than in ABB samples, and noticed that the majority of genes potentially involved in the host preference were different between the two species. At the functional level, the response to plant environment in adult females involved many processes, including the metabolism of carbohydrates, lipids, proteins, and amino acids; detoxification mechanisms and immunity; and the chemosensory repertoire (as expected). Until now, most of the olfactory receptors described in Ostrinia spp. had been tested for their putative role in pheromone recognition by males. Here we observed that one specific olfactory receptor was clearly associated with ECB’s discrimination between maize and mugwort conditions, highlighting a potential new candidate involved in plant odor discrimination in adult females.ConclusionsOur results are a first step toward the identification of candidate genes and functions involved in chemosensory processes, carbohydrate metabolism, and virus and retrovirus dynamics. These candidates provide new avenues for research into understanding the role of divergent selection between different environments in species diversification.
Highlights
Divergent selection has been shown to promote speciation in many taxa and especially in phytophagous insects
European corn borer (ECB)- and adzuki bean borer (ABB)-ref assemblies and annotation We sequenced RNA from adult ECB and ABB moths sampled from a previous experiment [59], where phenotypic and behavioral traits in moths faced with different plant environments were measured
Three plant environments were tested: i) “maize” conditions where only maize plants were available, they being the usual host for ECB; ii) “mugwort” conditions where only mugwort plants were available, they being the usual host for ABB; and iii) “choice” conditions where both plants were available Twenty-four RNA samples corresponding to two repetitions, three experimental conditions, two tissues and two moth species (ABB and ECB) were sequenced with HiSeq technology, and raw reads were assembled to build de novo transcripts
Summary
Divergent selection has been shown to promote speciation in many taxa and especially in phytophagous insects. The first is a well-known maize pest, whereas the second is a polyphagous species associated with various dicotyledons Their specialization to host plants is driven by morphological, behavioral and physiological adaptations. Previous studies have shown that ECB and ABB display marked behavior with regard to plant choice during oviposition, involving specific preference and avoidance mechanisms. Our goal was to identify the mechanisms underlying this host-plant specialization in adult females through an analysis of their gene expression. Speciation processes, by which populations diverge and become reproductively isolated, may be driven by divergent selection between different environments that affect various life history traits directly or indirectly related to fitness [12, 20, 22, 57, 72, 73]. The herbivorous host range results from these complex pluritrophic interactions, which occur throughout the entire life cycle of the insects [56]
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