Sea Lice
Genetic solution
RESULTS from a collaborative study between UK and Chilean researchers have furthered our understanding of genetic variation in resistance to sea lice in farmed Atlantic salmon, which is informing genomic selection strategies to develop more resistant strains. Two different lice species are the main culprits, with Lepeophtheirus salmonis affecting salmon producing countries in Europe (Norway, UK, Ireland and Faroes), and Caligus rogercresseyi causing problems in Chile.
The lice attach to the skin and feed on the mucus and blood of several occurrence of secondary infections. A multitude of prevention and control strategies are currently used, but none are fully effective.
These strategies include feed supplements, mechanisms, and even ‘lice-zapping’ lasers.Yet, the use of potentially environmentally damaging chemical treatments is still common, but lice are becoming resistant to many of the commonly used delousing drugs.
Selective breeding can contribute to sea lice prevention via harnessing naturally occurring genetic variation within commercial salmon stocks to iden of selection candidates can be enabled either by pedigree or genomic based approaches, the latter via genomic selection.
Previous studies have shown that moderate genetic variation in resistance to sea lice exists in Atlantic salmon populations, and salmon breeding companies are already using genomic selection approaches to improve resistance within their lines.
However, comparatively little is known about the This information can make genomic selection more effective, and potentially lead to target genes and pathways for development of treatments.
Professor Ross Houston (the Roslin Institute, University of Edinburgh), Dr Jose ManuelYañez (University of Chile), and Dr Diego Robledo (also Roslin) led a collaborative study that used various new genomic approaches to identify genes that contribute to genetic variation in resistance.This research was in collaboration with Benchmark Genetics Chile, which performs routine lice challenge experiments as part of its salmon breeding programme in order to include resistance to lice in its breeding goal.
Based on a large sample of post-smolt salmon challenged with caligus sea lice, the scientists correlated measures of lice counts (as a proxy of resistance) with tens of thousands of genetic markers dispersed throughout the genome. In addition, they performed a large scale sequencing experi substantially in their level of resistance to lice.
The team detected three genomic regions containing quantitative trait loci (QTL) affecting
They were able likely candidate genes and
resistance to lice, explaining between seven and 13 per cent of the genetic variation in lice counts. By bringing together the aforementioned sequencing data, they were able to identify likely candidate genes and mutations within these regions.
This was achieved by looking at key sets of genes that differ in their response to sea lice attachment between resistant and susceptible animals. Differentially expressed genes that are found within the genomic regions associated with resistance become high priority candidates as causative genes.
Further, the DNA sequencing results were used to identify all the genetic variants in these regions, and the likelihood of them having a functional effect was estimated.
Several candidate sea lice resistance genes and example, the researchers detected a variant of a gene on salmon chromosome 3 that may cause a truncation of a protein called TOB1 (which is involved in immune response by regulating T cells).
The scientists, including the collaborating breeding company Benchmark Genetics Chile, are planning to incorporate this functional genomic information to improve genomic selection.
on functional genetic variants in statistical models used to calculate resistance to sea lice of individual salmon broodstock, and this has the potential to increase selection accuracy.This would lead to faster improvement of genetic resistance in the salmon breeding programme.
The project was funded by the UK’s Newton Fund together with the Biotechnology and Biolog- ical Sciences Research Council (BBSRC).The paper describing the results has been accepted for publication in the journal Frontiers in Genetics and can be found at:
https://www.frontiersin.org/articles/10.3389/fgene.2019.00056/abstract