Revealing the genetic mechanisms underpinning the parasite-induced water-seeking behaviour of insects through RNA-seq

The water-seeking behaviour in arthropods infected by mermithid nematodes or nematomorphs is a classic example of host manipulation, yet how these parasites induce the behavioural change is poorly known. We investigated the molecular mechanisms at the basis of this aberrant behaviour in European earwigs ( Forficula auricularia ) infected with the nematode Mermis nigrescens . We performed comparative RNA-seq analysis at different stages of infection and behaviour manipulation in both the host and the parasite. We detected a total of 12,876 and 9,722 expressed genes in the earwig and nematode, respectively. Differential gene expression (DGE) analysis showed 673 genes upregulated and 593 downregulated in earwigs, and 2,672 genes upregulated and 2,293 downregulated in nematodes across all comparisons between stages of infection and parasite sizes. Clustering analysis produced six and four clusters of differentially expressed genes in earwigs and nematodes, respectively, based on temporal patterns of expression across stages of infection. With overrepresented analysis using gene ontology terms, we found that the earwig shows increased signalling and sensory pathways, while the nematode ramps up transport and secretory genes during manipulation. We found shared GATA transcription factor motif enriched in the differentially over expressed genes during manipulation in both host and the parasite. Our study provides valuable insights into candidate pathways and genes in the host and the parasite, improving our understanding of the molecular regulation of water-seeking behaviour.