How do Atlantic salmon adapt to their local environment? Perhaps the answer lies in their genes.

How do Atlantic salmon adapt to their local environment? Perhaps the answer lies in their genes.
2021-03-08

Blog on the SBS seminar (4th March 2021) from Dr Victoria Pritchard written by Max Vallarino, student from the “Meet the scientists” course

In an age where natural biodiversity is under greater threat than ever before, it is important to use every tool at our disposal when devising management plans for species of conservation or economic concern. Dr Victoria Pritchard of the Rivers and Lochs Institute in Inverness has proven that the use of modern genetic resources can be considered a key component of effective management.

So, where do Atlantic salmon fit in? As well as being one of the most globally important aquaculture species, Atlantic salmon are also threatened in the wild by over-fishing and habitat loss. Since wild Atlantic salmon numbers are declining, this species is a perfect candidate for genetic studies that can help inform management plans. Dr Pritchard and her colleagues have taken on the challenge of studying the Atlantic salmon life cycle and finding out how this can be shaped by genetics.

Atlantic salmon are born in freshwater, where they carry out the first stages of their life cycle. After a couple of years, these fish migrate to the ocean, where they undergo a great deal of growth before reaching sexual maturity. The Atlantic salmon life cycle ends when mature adults return to their river or stream of birth and breed. An interesting feature of this life cycle is that it can vary quite markedly between salmon populations. For example, some Atlantic salmon spend only a year at sea, mature quickly, then return to freshwater at quite a small size. Other Atlantic salmon spend many years at sea before reaching maturity and returning to freshwater at a much larger size. Atlantic salmon also show variation in exactly where they breed; some salmon will breed in very small streams, while others will breed at the bottom of large fast-flowing rivers. But, you might wonder, what is the point of having such a flexible life cycle?

Dr Pritchard’s interest lies in figuring out whether there is a genetic basis to these differences in life history between Atlantic salmon populations. She believes that different populations have each adapted to their local environment by slightly tweaking their life cycle and that specific genes might have made such changes possible. To test this theory, Dr Pritchard’s team studied Atlantic salmon genetics in two vast areas of Northern Europe: the Teno river (on the border between Norway and Finland) and the Kola peninsula (in north-west Russia). They took juvenile salmon from multiple sites across these study areas and compared their genetic makeup. Since these salmon came from distinct populations which had each been exposed to unique environmental conditions, Dr Pritchard expected to find genetic differences that could potentially be associated with this.

So, what were the key findings? Dr Pritchard’s team pinpointed a number of genetic regions that linked to life cycle differences across Atlantic salmon populations. They found genes that seemed to influence various strategies that a salmon will have during its life, including the number of years it will spend at sea, the time of year it will return to freshwater, and even the exact age it will reach maturity. Dr Pritchard’s results confirm what she set out to prove: that genetics can play a huge role in shaping the life cycle of Atlantic salmon populations. On top of this, it appears that wild salmon populations have evolved to develop the best genetic makeup (or rather, the best life cycle strategies) for adapting to their local environment. For example, Dr Pritchard’s results showed that Atlantic salmon born in large fast-flowing rivers are more likely to spend many years at sea and grow to large sizes before returning to freshwater; this makes sense because smaller salmon would likely find it more difficult to navigate fast-flowing rivers and complete their life cycle.

What is Dr Pritchard currently doing with these results in hand? Well, having identified some interesting genes in Scandinavian and Russian Atlantic salmon, she is now expanding her research to test whether these same genes are equally important elsewhere. Now that Dr Pritchard is based in Scotland, she would like to find out if any of these genes have allowed Atlantic salmon to adapt and thrive in different areas of the river Ness. She is even involved in work that has already proven the importance of certain Atlantic salmon genes in other species. For example, studies in North America have shown that these same genes might have allowed Pacific salmon and steelhead trout to adapt to their local environments.

Overall, Dr Pritchard’s work provides evidence that modern genetic tools can be used to inform management of Atlantic salmon and also other species. With Atlantic salmon habitats rapidly evolving due to climate change and manmade disturbances near streams and rivers, many salmon cannot keep up and do not have enough time to adapt accordingly. Using genetic information, it may be possible to highlight areas where local salmon populations are struggling and to then breed stock which are better suited to the new local environment. Perhaps the secret to effective management of Atlantic salmon has always been right in front of us, only hidden in salmon genes.

Published by The School of Biological Sciences, University of Aberdeen

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