[ad_1]
Although many of us draw their omega-3 fatty acids from fish oil, we tend to forget that fish need it as much as we do.
Now the research published in the journal Science shows how useful they can be: Omega-3 "jump" genes can actually be the key to spreading and diversifying fish species.
Jumping genes are DNA sequences that can copy and stick to different parts of a genome. They can be an essential driver of evolutionary diversity.
Docosahexaenoic acid (DHA), a compound essential for animal health, is one of the most important omega-3s. DHA is abundant in marine ecosystems but rare in freshwater environments. In seawater, various algae composing the diet of fish produce DHA, but it can also be made in small amounts by the fish itself.
Given how much DHA is needed, how do marine fish species colonize freshwater ecosystems – which has happened repeatedly over the course of history? 39; evolution?
Lead author, Asano Ishikawa, of the National Institute of Genetics and Advanced University of Advanced Studies (SOKENDAI), in Shizuoka, Japan, and a team of international scientists have sought to find the answer.
The team noted that the marine fish known as the Threespine Stickleback (Gasterosteus aculeatus) have successfully colonized freshwater habitats several times and on several continents during its evolutionary past.
In contrast, the Japanese sea stickleback, which is closely linked (G. nipponicus) did not colonize such environments at all. Ishikawa and his colleagues wondered why.
They first demonstrated that in the face of a poor diet in DHA, threespine stickleback can survive at a rate much higher than its counterpart. What they attributed to a metabolic gene called fatty acid desaturase 2 (FADS2) which is crucial for omega-3 synthesis.
What they then discovered is that the Pacific Threespine Stickleback populations have multiple copies of FADS2, unlike marine sticklebacks from Japan. This seemed to indicate that the higher number of FADS2 resulted in higher levels of DHA manufacture.
To confirm this, the team "has overexpressed the stickleback of the transgenic Sea of Japan. FADS2"That's proven to have much higher survival rates in low-DHA environments than their un-designed counterparts.
Taken together, they write, these 'data suggest that the bottom FADS2 The number of copies may be an obstacle to the colonization of DHA deficient freshwater niches by the Sea of Japan stickleback. "
Curiously, jumping genes, better known as transposons, could be the cause of the repetition of FADS2 in the genome of Threespine Stickleback and therefore their ability to adapt to freshwater habitats.
The transposons, say Jesse N. Weber and Wenfei Tong of the University of Alaska, USA, "are repetitive sequences that can fit, as well as any DNA between them, into other parts of the genome" .
In the same issue of Science, the couple writes that Ishikawa and his colleagues discovered that "transposons are responsible for multiple independent duplications of FADS2 in different populations of freshwater sticklebacks ".
Beyond that, the team also identified several copies of FADS2 in ray-finned fish (Actinopterygii class) with freshwater populations. This suggests a broader and more important role for FADS2 in the course of evolution.
This metabolic gene could therefore be one of the key elements that facilitated the adaptive radiation of fish species from marine to freshwater habitats.
[ad_2]
Source link