Immunity Of The Fittest? an article by: GF Willmetts

Reading in February that there is now a new race of mutant super-rats that we currently have in the UK who are immune to current rat poisons did stop me and think. The news reports says these rats mutated to beat the poisons but that seems at odd with genetics and more in line with the Lamarck theory that a species chooses what it needs to survive which has been disproved. For example, giraffes did not choose to grow long necks so they could eat food off high branches, they were just feeding when their shorter-necked relatives couldn’t find food to survive or just as likely, it allowed the longer necked variant to become more widespread and both found a way to survive. It doesn’t mean a variant can’t die out but is still down to random circumstances and as Charles Darwin so aptly put it, ‘Survival of the fittest’.

With rats, as they are widespread across the country than in an isolated group, this super-rat version is more likely to be a variant less susceptible to poison. Granted each female rat has 15 broods a year, subject to food supply and other predators, even a mutant breed would take some time to populate amongst non-mutated versions, let alone supersede it across the country at the same time. Except for one small detail, if you kill off all the other rats that don’t have that immunity then, of course, the super-rat would be all that’s left, except the old version is also still around. A yin and yang situation if you like. To have a lot of rats with the same mutation also tends to go against the idea of random mutation where there are a lot of variant species around to stand out.

Back when I was studying genetics, I came across the peppered moth up in the Midlands in the UK. It was a grey colour whose camouflage kept it from being eaten. However, with the Industrial Revolution, the factory effluent smoke darkened the trees and made this moth stand out and be eaten by predators. However, as written, this moth suddenly mutated into having a darker version and it survived. I doubt if any species can decide it will suddenly mutate to a different colour to survive. I would contest that the darker version was always around and most were eaten or not counted. When the environment changed, the balance of colour just made the grey version more susceptible to predators and easier to spot the dark version. Now the environment is more healthy, the grey variant has returned in quantity but I suspect it never really went away, just a reduction in numbers that made it hard to count.

Any species that continually has genetic variants is bound to produce favourable and dangerous mutations or even ones that won’t come into their own under the circumstances warrant it. Humans have this all the time. Man wasn’t always lactose tolerant but those who are thrived on milk but the non-tolerant variant is still out there. This applies to all kinds of foodstuffs that some of us may or may not be tolerant to. There’s even a tiny minority who don’t die of smoking but it’s not favourable odds that you’d be among them. With a genetic diversity, it improves the chances of survival of any variant. It is the variant types within each species that ensures its survival and purebreds might not always carry all the capable choices for them to come out. Any species is better being a mongrel than a thoroughbred.

Going back to the super-rat that is immune to poison, I suspect it was always there, just not breeding in quantities until those susceptible to poison died off. The problem is, what can you do about them? Find something that will kill them and it just leaves space for another rat variant that has its own immunity and you’re back to square one. It’s really just a demonstration of survival of the fittest and which variant will survive. Rats, as indeed any species in quantity, are going to have variants to survive against any conditions,

If you can’t remove a species like the rat then it makes more sense to promote an existing variant that breeds less often and maybe a shorter life-span. No, not too sure on the latter as it might make them breed more often. Maybe a variant that lives longer and breeds less. You can play a lot with the choices. Evolution then takes care of itself. It won’t remove the other rats but make them easier to control by having fewer of them about. After all, it doesn’t make sense to leave an uncontrolled gap where a different species, like the mouse or any other species get a foothold in and could take advantage of the situation. We have enough examples of that from introduced species to other environments to know how dangerous that is.

 

© GF Willmetts 2018