Genome complexity: variation within species (Introduction)

by David Turell , Saturday, December 10, 2016, 23:56 (2905 days ago) @ David Turell

David’s comment: It is becoming recognized that alternate metabolic pathways may be present in many species, as I noted in our previous discussions about bacteria responding to antibiotics (can't find the reference). The species is still one species. It is not a new evolutionary process as the articles headline proclaim.

dhw: May I suggest that if the killifish is able to cope so quickly with different pollutants, what it carries before the sites are polluted is not an alternative metabolic pathway anticipating whatever might happen next, but the ability to process new information and change its genome accordingly – which means it can construct a new metabolic pathway to cope with each new threat.

David: On the other hand the article clearly suggests there are variable individuals in the species some of whom can handle the pollution and survive.

Another article on killfish supports my viewpoint:

https://www.newscientist.com/article/2115635-fish-rapidly-adapt-to-pollution-thousands-...

"The team found dozens of changes in the fish that have evolved to help them tolerate pollutants such as dioxins and PCBs. “We have a picture of the entire adaptive genetic type,” says Whitehead.

"Many of these changes are in genes involved in a signalling pathway that has several roles in normal killifish, including in the immune system and for oestrogen signalling.

"This so-called AHR pathway also kicks in to deal with natural toxins. But if the pathway is switched on by pollutants during early development, it causes havoc. “It really messes things up,” says Whitehead.

"All the pollution-tolerant fish have several changes in AHR-related genes that stop it kicking in at the wrong time. However, evolution has not taken the same route in each population. Pollution-tolerant fish from different areas have different mutations in these genes.

"In addition, there are many changes in other genes to compensate for those in the AHR pathway. Because of its multiple roles, mutations that stop it being activated have many knock-on effects.

"The areas in which the killifish live started becoming polluted in the 1950s, so all these evolutionary changes arose over just dozens of generations. It could happen so quickly, says Whitehead, because there was already a lot of variation in the species. “Killifish have insect-like levels of genetic diversity,” he says. (my bold)

"Wirgin thinks the fact that killifish are territorial also helps them evolve fast, because it means that those from polluted areas are less likely to dilute their genes by interbreeding with those from pristine ones.

"Although killifish have evolved to thrive even in polluted areas, not all animals are so adaptable. In particular, there is much less diversity in large animals with smaller populations, meaning they may not be able to evolve fast enough to cope with the abrupt changes resulting from human activities. This is why it is vital to conserve diversity, says Whitehead."

Comment: Note the bolded area. The emphasis is on initial variability within the species to allow these adaptations to occur so rapidly. As pollution appears the most adaptable live and create more progeny that can withstand the changing environment. Still the same species, but adapted to a severe challenge.