Genome complexity: variation within species (Introduction)

by David Turell , Wednesday, December 14, 2016, 23:59 (2901 days ago) @ David Turell

I introduced the story about killfish on Dec. 9th and their rapid development of resistance to pollution. Here is another take, supporting my thought that the way to protection was already present:

https://www.washingtonpost.com/news/speaking-of-science/wp/2016/12/08/these-fish-evolve...

:But under ordinary circumstances, they struggle to cope with environmental pollutants: If you dropped an average killifish into toxic waters, it wouldn't last very long.

"That's why ecologists have puzzled over the populations that persist in the Elizabeth River, as well as in New Bedford Harbor in Massachusetts, the waters around Bridgeport, Conn., and New Jersey's Newark Bay — all former industrial sites now on the Superfund list. The fish there are able to withstand levels of pollution 8,000 times higher than the normal lethal limit. Clearly, they've had some adaptation that the rest of their species lacked. What was it?

"To find out, Whitehead and his colleagues sequenced the genomes of nearly 400 killifish from those four spots and four non-polluted areas nearby. The fish from the Superfund sites shared a set of mutations on a part of the genome related to a signaling pathway called aryl hydrocarbon receptor (AHR). The pathway regulates the immune system and release of the hormone estrogen, and, most importantly, it mediates toxicity. It's what makes killifish sensitive to pollutants. But without AHR, they can swim in toxic waters without getting hurt. 

"It's unusual for animals like killifish — which have life spans of years, not months — to evolve so rapidly, especially in four separate spots. To Whitehead, that suggests the mutation for the AHR deletion already existed in the larger killifish population, lying dormant like a superpower the animals didn't know they had. Once the changing environmental circumstances made the mutation useful for fish in polluted spots, it rapidly spread to the rest of the community. In real time, the animals evolved to adapt to their poisoned habitat. (my bold)

***

"When environmental shifts happen fast, animals can't wait around for the right, helpful mutation to occur, especially if they're animals with long life spans that don't reproduce very rapidly. They have to hope that this mutation already exists in the population, waiting to become useful.

"The latter scenario is more likely to happen when the population in question is larger and thus contains a larger degree of genetic diversity. The killifish population is one of the biggest.

“'Killifish top the charts in terms of vertebrates,” Whitehead said. “That’s probably what stacked the deck in their favor.”

"The situation holds a certain “tragic irony,” he said. Species that harbor large numbers of organisms and huge amounts of genetic diversity — think bugs and bacteria — are most able to adapt to new and deadly poisons. Unfortunately, those are usually the species that we're trying to tamp down. Meanwhile, populations humans hope to save, because they've been decimated by hunting or habitat loss, are least equipped to evolve.

“'There’s a critical level of genetic diversity that's necessary for the adaptive potential of species,” he continued. Most endangered species, by virtue of being endangered, don't have it." (my bold)

Comment: Please read my bolded areas especially. This supports my contention that challenged surviving species have original genetic diversity to help them survive. No inventions involved.