Salmon lice; (top) mature female with egg strings, (middle) mature female without egg stings, (bottom) immature louse. Image source: Wikimedia, Thomas Bjørkan
Of the many characteristics humans display, our ability to shape our own environments may be the most profound. The extent to which we are able to do this through the use of tools; physical, chemical and biological in nature, can have knock-on consequences for other organisms that inhabit our biosphere. One way in which human activity impinges on other organisms is through farming. Understanding the genetic and genomic effects on animal populations as a result of human intervention lies at the heart of research from Kevin Glover of the Institute of Marine Resarch, Norway and colleagues, who recently published a study in BMC Genomics on the human impact on salmon lice genetics.
Salmon lice are ectoparasites that feed on the skin, mucus and blood of salmon. Salmon aquaculture, practised extensively across the North Atlantic, provides a breeding ground for these organisms. Consequently salmon farmers aim to restrict the activity of the parasite via a range of pesticides, although the sustainability of this approach is under threat due to pesticide resistance.
Amongst marine researchers a number of genomic and genetic questions have remained unanswered about the aforementioned relationship between salmon-lice and salmon farming. Research by Glover and colleagues analysed whether pesticide resistance was generated in a number of locations across the North Atlantic region simultaneously or if the mutations were spread from a single origin. To address this the researchers focused on a SNP (single nucleotide polymorphism) array including 6000 markers and utilised salmon lice DNA samples from 12 locations covering an area from Canada to Northern Norway.
Via statistical analysis of the collected SNP data, the group were able to demonstrate the strong likelihood that the Atlantic salmon louse population is a continuous interbreeding one. This most likely is the result of the vast range across which the host salmon traverse the North Atlantic waterways.
Using a number of statistical methods the researchers were also able to demonstrate a reduction in genetic variation in certain specific regions of the salmon louse genome resulting from ‘selective sweeps’. Selective sweeps are strongly associated with selection events such as, in this case, pest control programs. These kinds of selection events have sweeping effects on the genetics of populations, as demonstrated in this study by the influence of human interference on salmon lice. To further confirm the link between pesticide resistance and ‘selective sweeps’ the group carried out linkage analysis between a region of the genome demonstrating a selective sweep and a region linked to EMB (a pesticide) resistance.
This study demonstrates the essential need for careful future management of pesticide use and pest management on highly mobile organisms in the North Atlantic.
Written by Derek Anane, Assistant Editor for BMC Genomics.