Faster rate of mutation in bacteria problem in isolated ecosystems?

July 15, 2015 6:12 AM

Spoilers for Kim Stanley Robinson's "Aurora" ahead. So, the story is like this: A multigenerational arkship is on it's way to Tau Ceti, they find their primary target for colonization hostile and discuss whether to move to another planet in the same system, live there in domes while terraforming it. One reason for not doing this is stated thusly:

“The problem is this: the spaces we have available to live in are too small to survive in for three thousand years. The main problem is the differential rates of evolution between the various orders of life confined to the space. Bacteria generally mutate at a rate far faster than larger species, and the effect of that evolution on the larger species is eventually devastating. This is one cause of the dwarfism and higher rates of extinction seen in island biogeography studies . And we are an island if there ever was one. And this Iris is not an Earth twin, nor an Earth analog. It is a Mars analog.

Robinson, Kim Stanley (2015-07-09). Aurora (Kindle Locations 3029-3033). Little, Brown Book Group. Kindle Edition.
Now I think that this argument is nonsense, but I am not sure about it. As I understand it the problem with isolated ecosystems is genetic drift, the founder effect and the bottleneck effect among others. I don't see how the fact that "Bacteria generally mutate at a rate far faster than larger species" should pose a special problem in an isolated ecosystem. Bacteria will and have always and everywhere mutated faster than larger organisms, because they have much shorter generation spans and it hasn't proven to be"eventually devastating" (Maybe it will with rising antibiotic resistance). So is there some merit to his argument? As he usually gets his science right there might be, but I am sceptical.

posted by SweetLiesOfBokonon to Science & Nature (6 answers total)

Just spitballing here, but I wonder if the idea is that the larger species have limited genetic diversity to work with in an "island" geography, while the bacteria don't really have that issue because even in the island there are still so many more of them. And so the faster evolution of the bacteria combined with the limited genetic material/limited potential for evolutionary changes among the larger organisms makes the bacteria potentially more dangerous. Like, if you only start off with 100 people at the beginning, it's less likely that one of them is carrying some gene that turns out to be resistant to whatever weirdness the bacteria cooks up, as compared to if you had whole continent of people to start with.
posted by rainbowbrite at 6:29 AM on July 15, 2015 [3 favorites]

I'm pretty sure this is nonsense. Island dwarfism is a thing, but it's my understanding that the generally-accepted explanation for it is that it's advantageous to be small when you're in a more circumscribed environment. That, or just plain genetic drift. It's not that there are bacteria stunting the growth of island-dwelling dwarf elephants, it's that there was evolutionary pressure to be small; most islands can't support a population of regular-size elephants.

Also over such a short time span as 3000 years, a bottleneck effect from the small founder population is going to be a much bigger deal than mutation rates. And shouldn't any respectable arkship have some kind of prescriptive breeding program in place for its residents? Cutting down on genetic drift, period? Whether something like that's going to be sustainable over 3000 years is debatable, but really the bacteria seem like the least of their problems.
posted by mskyle at 8:11 AM on July 15, 2015 [1 favorite]

There were some buffalo left on an island off the coast of California, probably by an irresponsible film crew. They are smaller than is typical for American buffalo. Periodically, they cull the heard and ship some back to where you typically find buffalo. They rapidly gain 100 pounds and a thicker coat. So we have pretty strong evidence that island dwarfism is due to being on an island, possibly a combination of limited resources and unusual climate (the thicker fur and greater weight are partly to survive the harsh winters on the mainland, neither of which is needed on this coastal island with a mild climate), not genetic or microbial causes per se.

I am pretty sure the piece you quoted is wrong on several fronts. For one thing, since our digestion is dependent on gut bacteria and our gut constitutes about 70% of our immune system, our relationship to bacteria is a great deal more complicated than just battling it out with them for survival. Furthermore, we are only just beginning to document how diet and environment impact the gut ecosystem. We are also only just now beginning to try to understand environmental factors that play a part in microbial evolution. Evolution does not happen in a vacuum or just as some random roll of the dice. Environmental factoirs strongly influence it. When environmental pressures are high, you see more random, crazy-assed mutations while bacteria frantically search for a means to survive. IIRC, they also have mechanisms for spreading mutations that are successful in very deadly environments, which is part of how you get antibiotic resistent super bugs.

For another, there are situations where larger organisms have the survival advantage, for example in facing temperature changes. This fact has long been used by humans as a treatment modality, starting with the basic mechanism of fever but also including hot and cold treatments.

I would like to think that we will have a more sophisticated understanding of such things before we try to colonize space. To me, this sounds like a fear-based concept of our current struggles with antibiotic resistent infections and other infection control issues we are running into due to unprecedented high populations, international travel, etc. We all know that lots of native americans died because europeans brought infectuons to which they had no immunity. We have guilt but not fear and we seem to believe native american diseases were not a problem for europeans. Most likely, the reality is that it ran through a smaller population of explorers and if you had no immunity, you did not live to carry it back to europe, which was a long ways away. Modern travel has put a stop to that pattern of one way transmission and made it possible to bring something back before you are symptomatic and infect your countrymen. So we have a lot of new threats that are not yet solved problems and thenthose fears make their way into our fiction.
posted by Michele in California at 10:21 AM on July 15, 2015

I think it makes sense in a only in mathematical model where there would be no intervention against selection pressure. Humans can clearly intervene against negative selection forces, but if they couldn't, our slower mutation rate would make us less adaptable to a catastrophic event as compared to bacteria, which are more likely be able to adapt based on their argument.
posted by waving at 12:27 PM on July 15, 2015

The bacterial stuff sounds like nonsense to me, unless there's a non-desirable selective pressure they are particularly worried about.
posted by maryr at 1:45 PM on July 15, 2015

I think you're misunderstanding the type of bacteria being discussed: in the context of the novel he's much more interested in the symbiotic relationship between humans and bacteria (as Michele in California suggests) than in the adversarial one. Basically, the claim is that the ecosystem inside the spaceship has basically no margin for error in terms of remaining stable for the reproduction of human society: if the necessary ("good") bacteria in the system get sufficiently out of sync with the plants and with the people then the system will crash and the people will die, just as surely as if some disease-causing superbacteria evolves in the system. The spacecraft's ecosystem is both artificial (so it doesn't properly match the terrestrial natural system, provoking the bacteria to evolve in ways that are maladaptive from a human perspective) as well as maximally isolated, meaning they can't change their diet or gather new seeds if things get bad. The claim isn't that they would DEFINITELY all die but that the system they depend on is too fragile and too prone to disruption to risk the trip.
posted by gerryblog at 8:36 PM on July 15, 2015