Abstract
Outbreaks of locust populations repeatedly devastate economies and ecosystems in large parts of the world. The consequent behavioural shift from solitarious to gregarious and the concomitant changes in the locusts’ biology are of relevant scientific interest. Yet, research on the main locust species has not benefitted from recent advances in genomics. In this first RNA-Seq study on Schistocerca gregaria, we report two transcriptomes, including many novel genes, as well as differential gene expression results. In line with the large biological differences between solitarious and gregarious locusts, almost half of the transcripts are differentially expressed between their central nervous systems. Most of these transcripts are over-expressed in the gregarious locusts, suggesting positive correlations between the levels of activity at the population, individual, tissue and gene expression levels. We group these differentially expressed transcripts by gene function and highlight those that are most likely to be associated with locusts’ phase change either in a species-specific or general manner. Finally, we discuss our findings in the context of population-level and physiological events leading to gregariousness.
Highlights
Phase polyphenism of locusts is one of the most notorious cases of phenotypic plasticity due to its association with extreme increase in population size and the consequent devastating effects on the ecosystem and economy of the affected area
Almost all studies focusing on the molecular aspects of the phase change in locusts use either L. migratoria or S. gregaria[12,13,16,18,33,41]
For the first time, the changes in gene expression levels that differentiate solitarious and gregarious S. gregaria locusts and confirm 59% of the ESTs Sanger-sequenced by Badisco et al.[45]
Summary
Phase polyphenism of locusts is one of the most notorious cases of phenotypic plasticity due to its association with extreme increase in population size (outbreak) and the consequent devastating effects on the ecosystem and economy of the affected area. Gregarious locusts have a more active immune response whereas solitarious locusts have longer lifespan and even an extra molt[24] All these differences are due to changes in gene expression that are triggered by changes in environmental stimuli that result from the increase in population density. A neuropeptide related to aggressive behavior, learning and circadian rhythms in insects[35,36], was proposed as a trigger of gregariousness in S. gregaria[18,37] It seems to have the opposite effect in L. migratoria[38]. The molecular aspects of the phase change differ between species (see examples above)
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