Effects of larval crowding on the transcriptome of Drosophila simulans (Pt)
Larval crowding is one common ecological stressor for many insect species. In Drosophila, high larval density alters multiple, widely-studied phenotypes including life history traits, morphology and behavior. Larval crowding imposes stress on multiple levels including the accumulation of waste products, limited nutrition and spatial limitations.  Simple contrasts of high- and low-density conditions cannot connect a phenotype to a specific stressor. Here, we take advantage of the variable developmental rates at high density conditions to overcome this limitation. RNA-Seq of adult males of the same age, but exposed to different food qualities, enabled us to dissect the molecular basis of traits responding to different stressors. We find that the expression of genes related to nutrition and detoxification reflects the poorer food quality at later stages. The majority of differentially expressed genes is, nevertheless, unrelated to these two stress factors, but points to space limitation as a prominent stressor. The pronounced differences in gene expression provide a robust understanding of the physiological response to different stressors triggered by high larval density.