Environmental Changes Drives the Transcriptome and Gene Regulation Plasticity During Sea Lice Infestation

The sea louse, Caligus rogercresseyi, is one of the main concerns in the Chilean salmon industry. The free-living copepodid stage can recognize the host and initiate the parasitic phase, where environmental factors can shape the host recognition process. This study aimed to explore the ecological influence on the transcriptome of copepodids infesting Atlantic salmon experimentally exposed to different salinity and temperature (S/T) conditions. Herein, 200 salmon were infested with 35 copepodids per fish previously acclimatized to four S/T treatments: 32 and 26 PSU; 8 and 16°C. After 48 h of infestation, the attached copepodids from each experimental group were counted and digitalized for geometric morphometric analysis. Copepodids were then collected for RNA sequencing to analyze transcriptome modulation and gene regulation. Morphological changes in copepodids were mainly associated with temperature rather than salinity conditions. The transcriptome survey revealed molecular signatures related to salinity and temperature changes, where salinity drives the gene expression of copepodids. Notably, specific genes, such as those encoding cuticle proteins and trypsin-like kinases, were regulated by all three post-transcriptional mechanisms assessed: alternative splicing, miRNA, and gene fusion. The transcriptome analysis revealed that trypsin-like kinase genes exhibited upregulation and downregulation across the various S/T conditions. In contrast, cuticle protein genes were consistently downregulated in the 32 PSU/8°C, 26 PSU/8°C, and 26 PSU/16°C groups compared to the 32 PSU/16°C control. This suggests that the three post-transcriptional mechanisms may exert a combined influence on the expression of specific genes, potentially driven by salinity and temperature environmental conditions in sea lice biology.