Abstract
BackgroundOur main purpose was to evaluate the expression of plastic and evolved genes involved in ecological speciation in the noctuid moth Spodoptera frugiperda, the fall armyworm (FAW); and to demonstrate how host plants might influence lineage differentiation in this polyphagous insect. FAW is an important pest of several crops worldwide, and it is differentiated into host plant-related strains, corn (CS) and rice strains (RS). RNA-Seq and transcriptome characterization were applied to evaluate unbiased genetic expression differences in larvae from the two strains, fed on primary (corn) and alternative (rice) host plants. We consider that genes that are differently regulated by the same FAW strain, as a response to different hosts, are “plastic”. Otherwise, differences in gene expression between the two strains fed on the same host are considered constitutive differences.ResultsIndividual performance parameters (larval and pupal weight) varied among conditions (strains vs. hosts). A total of 3657 contigs was related to plastic response, and 2395 contigs were differentially regulated in the two strains feeding on preferential and alternative hosts (constitutive contigs). Three molecular functions were present in all comparisons, both down- and up-regulated: oxidoreductase activity, metal-ion binding, and hydrolase activity.ConclusionsMetabolization of foreign chemicals is among the key functions involved in the phenotypic variation of FAW strains. From an agricultural perspective, high plasticity in families of detoxifying genes indicates the capacity for a rapid response to control compounds such as insecticides.
Highlights
Our main purpose was to evaluate the expression of plastic and evolved genes involved in ecological speciation in the noctuid moth Spodoptera frugiperda, the fall armyworm (FAW); and to demonstrate how host plants might influence lineage differentiation in this polyphagous insect
If the initial preference for a new host plant is a plastic response, in the sense of the ability of a single-genotype organism to react to a novel environment and to produce different phenotypes [11, 13], the evolutionary mechanism behind the use of alternative host plants in the distributional range of an insect, leading to an increase in reproductive isolation, can follow the developmental-plasticity hypothesis proposed by WestEberhard [12]
corn strain (CS) larvae were significantly heavier than rice strains (RS) larvae when they were fed on rice and on the artificial diet
Summary
Our main purpose was to evaluate the expression of plastic and evolved genes involved in ecological speciation in the noctuid moth Spodoptera frugiperda, the fall armyworm (FAW); and to demonstrate how host plants might influence lineage differentiation in this polyphagous insect. If the initial preference for a new host plant is a plastic response, in the sense of the ability of a single-genotype organism to react to a novel environment and to produce different phenotypes [11, 13], the evolutionary mechanism behind the use of alternative host plants in the distributional range of an insect, leading to an increase in reproductive isolation, can follow the developmental-plasticity hypothesis proposed by WestEberhard [12] According to this model, adaptive selection of plastic phenotypes occurs in two steps: 1) a novel environmental factor affects plastic phenotypes, leading to novel variants; 2) novel variants affected by environmental recurrences of the initial stimulus are selected to produce evolutionary genetic change that can become fixed by genetic assimilation [13]. Plasticity in one trait can influence the variation and selection in linked or correlated traits [11]
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