Aging features of the migratory locust at physiological and transcriptional levels

Vesicular Stomatitis Virus Elicits Early Transcriptome Response in Culicoides sonorensis Cells

Viruses that are transmitted by arthropods, or arboviruses, have evolved to successfully navigate both the invertebrate and vertebrate hosts, including their immune systems. Biting midges transmit several arboviruses including vesicular stomatitis virus (VSV). To study the interaction between VSV and midges, we characterized the transcriptomic responses of VSV-infected and mock-infected Culicoides sonorensis cells at 1, 8, 24, and 96 h post inoculation (HPI). The transcriptomic response of VSV-infected cells at 1 HPI was significant, but by 8 HPI there were no detectable differences between the transcriptome profiles of VSV-infected and mock-infected cells. Several genes involved in immunity were upregulated (ATG2B and TRAF4) or downregulated (SMAD6 and TOLL7) in VSV-treated cells at 1 HPI. These results indicate that VSV infection in midge cells produces an early immune response that quickly wanes, giving insight into in vivo C. sonorensis VSV tolerance that may underlie their permissiveness as vectors for this virus.

PLIN2-induced ectopic lipid accumulation promotes muscle ageing in gregarious locusts

Ageing plasticity represents the flexibility of the ageing process in response to non-genetic factors, occurring commonly in animals. However, the regulatory mechanisms underlying ageing plasticity are largely unclear. The density-dependent polyphenism of locusts, Locusta migratoria, displays dramatic lifespan divergence between solitary and gregarious phases, providing a useful system for studying ageing plasticity. Here, we found that gregarious locusts displayed faster locomotor deficits and increased muscle degeneration on ageing than solitary locusts. Comparative transcriptome analysis in flight muscles revealed significant differences in transcriptional patterns on ageing between two phases. RNA interference screening showed that the knockdown of the upregulated PLIN2 gene significantly relieved the ageing-related flight impairments in gregarious locusts. Mechanistically, the gradual upregulation of PLIN2 could induce the accumulation of ectopic lipid droplets and triacylglycerols in flight muscles during the ageing process. Further experiments suggested that ectopic lipid accumulation led to an ageing-related β-oxidation decline through limiting fatty acid transport and content. These findings reveal the key roles of lipid metabolism in the differences of muscle ageing between solitary and gregarious locusts and provide a potential mechanism underlying environment-induced muscle ageing plasticity.

Neuroendocrinal and molecular basis of flight performance in locusts

Insect flight is a complex physiological process that involves sensory and neuroendocrinal control, efficient energy metabolism, rhythmic muscle contraction, and coordinated wing movement. As a classical study model for insect flight, locusts have attracted much attention from physiologists, behaviorists, and neuroendocrinologists over the past decades. In earlier research, scientists made extensive efforts to explore the hormone regulation of metabolism related to locust flight; however, this work was hindered by the absence of molecular and genetic tools. Recently, the rapid development of molecular and genetic tools as well as multi-omics has greatly advanced our understanding of the metabolic, molecular, and neuroendocrinal basis of long-term flight in locusts. Novel neural and molecular factors modulating locust flight and their regulatory mechanisms have been explored. Moreover, the molecular mechanisms underlying phase-dependent differences in locust flight have also been revealed. Here, we provide a systematic review of locust flight physiology, with emphasis on recent advances in the neuroendocrinal, genetic, and molecular basis. Future research directions and potential challenges are also addressed.

Locust density shapes energy metabolism and oxidative stress resulting in divergence of flight traits

Migratory locusts display striking phenotypical plasticity. Gregarious locusts at high density can migrate long distances and cause huge economic losses of crops. By contrast, solitary locusts at low density have limited ability in long-distance flight. However, the mechanisms underlying such flight capacity variation are poorly understood. Here, we found that the flight muscle of solitary locusts has a higher catabolic capacity that is associated with greater reactive oxygen species (ROS) generation during high-velocity flights. By contrast, a relatively lower catabolic capacity in gregarious locusts is associated with lower ROS generation during long-distance flights. This finding uncovers the metabolic mechanism of locust flight trait alteration in response to density changes and enhances our understanding of the biological processes enabling locust migration.

Flight ability is essential for the enormous diversity and evolutionary success of insects. The migratory locusts exhibit flight capacity plasticity in gregarious and solitary individuals closely linked with different density experiences. However, the differential mechanisms underlying flight traits of locusts are largely unexplored. Here, we investigated the variation of flight capacity by using behavioral, physiological, and multiomics approaches. Behavioral assays showed that solitary locusts possess high initial flight speeds and short-term flight, whereas gregarious locusts can fly for a longer distance at a relatively lower speed. Metabolome–transcriptome analysis revealed that solitary locusts have more active flight muscle energy metabolism than gregarious locusts, whereas gregarious locusts show less evidence of reactive oxygen species production during flight. The repression of metabolic activity by RNA interference markedly reduced the initial flight speed of solitary locusts. Elevating the oxidative stress by paraquat injection remarkably inhibited the long-distance flight of gregarious locusts. In respective crowding and isolation treatments, energy metabolic profiles and flight traits of solitary and gregarious locusts were reversed, indicating that the differentiation of flight capacity depended on density and can be reshaped rapidly. The density-dependent flight traits of locusts were attributed to the plasticity of energy metabolism and degree of oxidative stress production but not energy storage. The findings provided insights into the mechanism underlying the trade-off between velocity and sustainability in animal locomotion and movement.