

Did learning to fly give bats super-immunity? - betadreamer
http://www.newscientist.com/article/dn23020-did-learning-to-fly-give-bats-superimmunity.html

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csense
I assumed from the headline that this would be a stupid article, but I took
the time to read it anyway and found that this assumption was wrong.

The premise sounds quite solid: The unique challenges of being a flying mammal
require spending lots of energy. Which leads to lots of free radicals. Which
leads to lots of DNA damage. Which increases selective pressure for DNA
repair.

Evolution normally doesn't select for organisms that are able to survive
aging, because, from the standpoint of natural selection, once your
reproductive years are past, your survival doesn't matter.

That aging resistance would be an incidental benefit of general DNA repair
mechanisms that evolved in response to a lifestyle that encourages free
radical formation makes a lot of sense. The specific molecules and reactions
involved in bats probably will provide important clues to the aging process in
mammals, even if the adaptations in bats can't be translated directly into
treatments for humans.

How immunity and disease fits into this picture is less clear from the
article. But the aging angle alone is enough to make this research very
interesting.

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thaumasiotes
> Evolution normally doesn't select for organisms that are able to survive
> aging, because, from the standpoint of natural selection, once your
> reproductive years are past, your survival doesn't matter.

The logic is actually a bit deeper than this. There's no reason you couldn't
have an organism that "survived aging", and that could reproduce indefinitely.
Obviously, given a potentially unlimited reproductive span, selection would
come in on the side of longer lifetimes.

As I've seen it presented, the logic of organism deterioration with age is
that accidents happen, which means that, if you happen to have a life strategy
which makes you momentarily better off, but permanently worse off, you may die
of unrelated causes before suffering a net loss. As long as that can happen,
we should observe aging: young organisms boosting their performance at the
expense of their own future selves.

(as an example: imagine you impress a girl by doing some death-defying stunt,
and suffer more physical strain than your body is really designed for. If you
were going to live forever, that might be a bad idea. If you're not, then
maybe impressing the girl is worth the lower physical fitness you have
afterwards.)

~~~
csense
> if you happen to have a life strategy which makes you momentarily better
> off, but permanently worse off, you may die of unrelated causes before
> suffering a net loss

This is true, but irrelevant to the present discussion. If you can live and
reproduce forever -- or for a very long time -- then the -EV of "permanently
worse off" exceeds the +EV of "temporarily better off."

My understanding of why we didn't evolve to have better gene repair and longer
lives is that the ideal death and mutation rates in terms of _species_
survival is some finite number greater than zero. Near-immortality, eternal
youth and perfect genome repair would be great from an _individual_
perspective, but from a _species_ perspective, those things reduce the ability
for genetic innovation. Too many mutations are bad, but not enough mutations
are also bad.

I would guess that the bats get around this by getting so much extra EV from
occupying the unique ecological niche of "flying mammal" that the ability to
occupy that niche overwhelms the negative aspects of a smaller mutation rate.

~~~
AnthonyMouse
>I would guess that the bats get around this by getting so much extra EV from
occupying the unique ecological niche of "flying mammal" that the ability to
occupy that niche overwhelms the negative aspects of a smaller mutation rate.

You're assuming a smaller mutation rate. The article points out that bats
generally don't live to die of old age, something else usually gets them
first.

A longer _theoretical_ lifespan doesn't reduce the mutation rate if lifespans
in practice are still modest. (If the first couple of hits on Google are any
indication, bats typically live for a couple of decades.)

~~~
csense
> if lifespans in practice are still modest

They aren't. The article says: "For an animal of their size, [bats] also age
very slowly..."

I'm assuming that, without their gene repair mechanism, they would have been
more in line with other animals their size, and occasionally died of old age.
So the gene repair mechanism _does_ extend the bats' lifespan.

To do good science, of course, you'd have to confirm this by an experiment to
raise some bats that lack the gene repair mechanism and measure their deaths
due to old age against a control group. Or better yet, do a fantastically
expensive long-term experiment comparing bat colonies with and without the DNA
repair mechanism, and measure their genetic drift over time.

Of course, I haven't done those experiments. If someone else does them, and
shows results contradictory to my assumption, it'll be a great scientific
discovery. But in the absence of evidence to the contrary, it seems like it's
a safe bet that the DNA repair mechansim would reduce mutation rates on its
own, and anything that makes the bats live longer would also reduce mutation
rates on its own, and having both longevity and DNA repair together would
reduce mutation rates at least as much as either by itself.

You may say decades of lifespan is "modest" by human standards, but much more
relevant comparisons would be to bats without the DNA repair mechanism -- or,
if data is lacking on those, to closely related mammals of similar size.

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hughlomas
Consider it from the disease's perspective.

Ebola doesn't 'target' humans. Ebola's obvious symptoms and mortality rate in
humans limit its ability to spread efficiently. The flu virus or cold virus
has been far more successful in penetrating the human ecosystem. Perhaps Ebola
has been selected for being stable in the bat ecosystem. The mobility of bats
also makes them an excellent transmission vector, which a virus would ideally
want to be non-symptomatic.

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lostlogin
Given the massive die offs from the fungal infection that is completely
devastating US bat populations, I'd say their immune systems may be unique,
but they aren't miraculous. The outlook for North American bats is very grim.
<http://en.m.wikipedia.org/wiki/White_nose_syndrome>

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gus_massa
Very strange, I'd like to see more evidence.

Is there some analogous adaptation for birds? Flying / non-flying birds?

~~~
abecedarius
Birds are also long-lived, compared to mammals of similar size. One of Nick
Lane's books discussed this and something about their adaptations against
damage from respiration -- either _Oxygen_ or _Power, Sex, Suicide_ , I forget
which.

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sukuriant
Why are bats the litmus test for rabies, then? That just seems a bit odd. And
why is rabies so prevalent/dangerous in bats that even breathing the air in
bat caves can get you the disease?

~~~
huggah
Dangerous for humans, you mean. The fact that a species can survive while
being so disease-ridden that they routinely kill the animals they infect seems
to lend credence to the "super-immunity" claim.

I'm not sure this is actually the case for bats, but assuming your statement
is true, it seems to be evidence for the presence of super-immunity, rather
than against.

~~~
executive
Dangerous for some humans, you mean. Clearly not dangerous for Mr. Wayne.

