The sea louse Caligus rogercresseyi is the main ectoparasite species affecting Chilean salmon industry. Hydrogen peroxide (H2O2) has been introduced as a delousing treatment to control lice infestations. The suggested mechanism is based on the formation of bubbles in the copepod hemolymph inducing a mechanical paralysis, detaching the parasite from the host. However, the molecular mechanisms underlying the response and potential resistance to H2O2 are not yet fully elucidated. This study aimed to expand the molecular knowledge through the single nucleotide polymorphisms (SNPs) discovery involved in the response of C. rogercresseyi against H2O2 .
First, t ranscription expression of immune-related, antioxidant system, chemosensory receptors, secretome and cuticle formation genes were evaluated in individuals exposed to 3 concentrations of H2O2 (360, 744 and 1080 mg L-1 ). Then, novel SNPs in catalase, superoxide dismutase, serpin, cuticle 7, cuticle 19 and trypsin 5 genes were validated in individuals from 3 populations differing in H2O 2 sensitivity according to bioassays results.
U pregulation of genes related to antioxidant system, secretome and cuticle formation in exposed individuals were observed. Moreover, results from SNPs allele frequencies suggest that particular alleles of catalase, superoxide dismutase and serpin genes might be involved in the reduced susceptibility to H2O2 in the Potentially-Resistant (P-R) population (Table 1).
This study contributes to a better understanding of C. rogercresseyi responses to H2O2 , providing new insights into the molecular mechanisms involved in drug resistance . Moreover, the novel SNPs found here could be a potential useful tool for H2O2 sensitivity evaluation in lice populations. Further studies will be needed to validate these polymorphisms as a molecular complementary tool for H2O2 sensitivity status evaluation. Nevertheless, our investigation will have important implications for H2O2 treatment strategies for sea lice.
Funding: ANID-Chile through the grant FONDECYT (#11200813), and FONDAP (#15110027).