The same basic kind of fish, called the stickleback, inhabits salt or fresh water and lakes or streams. Strikingly, however, those living in salt water are much larger and have different colors and different scale armor than their freshwater counterparts with whom they can interbreed. One generation of the marine variety can give rise to a generation of freshwater versions, and vice versa. Are these fish evolving, or were they created to make these kinds of body changes within their kind?
Researchers scoured DNA from 22 representative stickleback fishes for any sequence differences that might be linked to saltwater versus freshwater environments. Their research should help answer questions about how fishes adapt to their surroundings and how closely those processes match standard ideas about evolution.
According to the Nature study, the team gathered interesting results, including specific sites of DNA differences that were directly linked to the fish’s environment. They found the different sequences interspersed throughout all the fish’s chromosomes. Also, fewer of those sequences were genes than those that were sequences that regulated genes. Both the genes and regulatory sequences were very similar between all the fishes studied, showing that they have been resistant to mutational changes. The authors wrote that since the different environment-linked DNA sites “do not cause protein-coding changes, they also probably contribute to adaptive divergence by regulatory alterations.”1….
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