Phenotypic and Differential Gene Expression Analyses of Phase Transition in Oedaleus Asiaticus under High-Density Population Stress

SIMPLE SUMMARY: Oedaleus asiaticus (Bey-Bienko) is one of the most dominant locust species in grassland and pastoral areas in Inner Mongolia of northern China. It is highly abundant and usually makes up more than half (sometimes even up to 90%) of the local locust community in locust outbreaks. Locust aggregation is a prerequisite for a locust outbreak, requiring phase change from solitary to gregarious individuals. In this study, we used Illumina sequencing technology to screen 3911, 7478, 3142, and 1852 differentially expression genes (DEGs) in Oedaleus asiaticus during phase transition after 1, 3, 5, and 7 days of high-density treatment, respectively, and recorded the transition from green to brown individuals in different stages. The change in expression patterns of JHAMT, JHEH, DIB, HPD, TAT, PAH, DDC, CSP, and TO, which are the key genes of phase transition relevant metabolic pathways, at different stages of the phenotypic transformation suggests their regulatory role in the phenotypic process. This study improves the scientific understanding of phase variation in locusts; the learning can be applied to other insects. ABSTRACT: The high-density-dependent phase change from solitary to gregarious individuals in locusts is a typical example of phenotypic plasticity. However, the underlying molecular mechanism is not clear. In this study, first, Oedaleus asiaticus were treated with high-density population stress and then analyzed by Illumina sequencing on days 1, 3, 5, and 7 of the body color change to identify the stage-specific differentially expressed genes (DEGs). The KEGG pathway enrichment analysis of the identified DEGs revealed their role in metabolic pathways. Furthermore, the expression patterns of the nine key DEGs were studied in detail; this showed that the material change in locusts began on the third day of the high-density treatment, with the number of DEGs being the largest, indicating the importance of this period in the phase transition. In addition, the phenotypic change involved several key genes of important regulatory pathways, possibly working in a complex network. Phenotypic plasticity in locusts is multifactorial, involving multilevel material network interactions. This study improves the mechanistic understanding of phenotypic variation in insects at the genetic level.