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bioRxiv · 10.1101/815316

Host gill attachment enables blood-feeding by the salmon louse (Lepeophtheirus salmonis) chalimus larvae, and alters parasite development and transcriptome

Heggland, E. I.·Dondrup, M.·Nilsen, F.·Eichner, C.
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Abstract

Blood-feeding is a common strategy among parasitizing arthropods, including the ectoparasitic salmon louse (Lepeophtheirus salmonis), feeding off its salmon hosts skin and blood. Blood is rich in nutrients, among these iron and heme. These are essential molecules for the louse, yet their oxidative properties render them toxic to cells if not handled properly. Blood-feeding might therefore alter parasite gene expression. We infected Atlantic salmon with salmon louse copepodids and sampled the lice in two different experiments at day 10 and 18 post infestation. Parasite development and presence of host blood in their intestines were determined. We find that lice start feeding on blood when becoming mobile preadults if sitting on the fish body, however they may initiate in blood-feeding at the chalimus I stage if attached to gills. Lice attached to gills develop at a slower rate. Lice of similar instar age from gills versus lice from skin epidermis were analyzed for gene expression by RNA-sequencing in samples taken at day 10 for both experiments and at day 18 for one of the experiments. By differential expression analysis, we found 355 transcripts elevated in lice sampled from gills and 202 transcripts elevated in lice sampled from skin consistent in all experiments. Genes annotated with "peptidase activity" are among the ones elevated in lice sampled from gills, while in the other group genes annotated with "phosphorylation" and "phosphatase" is pervasive. Transcripts elevated in lice sampled from gills are often genes relatively highly expressed in the louse intestine compared with other tissues, while this was not the case for transcripts found elevated in lice sampled from skin. In both groups, more than half the transcripts are from genes higher expressed after attachment. In conclusion, blood-feeding results in an alteration in gene expression, and a premature onset of blood-feeding likely causes the parasite to develop at a slower pace.

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Heggland, E. I., Dondrup, M., Nilsen, F., Eichner, C.. 2019-10-28. Host gill attachment enables blood-feeding by the salmon louse (Lepeophtheirus salmonis) chalimus larvae, and alters parasite development and transcriptome. https://doi.org/10.1101/815316

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