Transcriptome profiling of a multiuse model species Lymnaea stagnalis (Gastropoda) for ecoimmunological research

Host immune function can contribute to numerous ecological/evolutionary processes. Ecoimmunological studies, however, typically use one/few phenotypic immune assays and thus do not consider the complexity of the immune system. Therefore, "omics" resources that allow quantifying immune activity across multiple pathways are needed for ecoimmunological models. We applied short-read based RNAseq (Illumina NextSeq 500, PE-81) to characterise transcriptome profiles of a multipurpose model species Lymnaea stagnalis (Gastropoda). We used a genetically diverse snail stock and exposed individuals to immune elicitors (injury, bacterial/trematode pathogens) and changes in environmental conditions that can alter immune activity (temperature, food availability). Immune defence factors identified in the de novo assembly indicated uniform aspects of molluscan immunity: pathogen-recognition receptors (PRR) and lectins activate Toll-like receptor (TLR) pathway and cytokines that regulate cellular and humoral defences. However, also apparent differences to other taxa were detected (i.e., modest numbers of antimicrobial peptides and fibrinogen related proteins). Identified factors also indicate that several of them might contribute to the phenotypic immune assays used on this species. Experimental treatments revealed factors from non-self recognition (lectins) and signalling (TLR pathway, cytokines) to effectors [e.g., antibacterial proteins, phenoloxidase (PO) enzymes] whose gene expression depended on immune activations and environmental conditions, as well as components of snail physiology/metabolism that may drive these effects. Interestingly, gene expression of many factors (e.g., PRR, lectins, cytokines, PO enzymes, antibacterial proteins) showed high among-individual variation. Such factors are important to include in ecoimmunological research because they may explain among-individual differences in parasite resistance and fitness in natural populations.