Two tales of surprising longevity in the animal kingdom

June 12, 2019 9:41 PM

In mammals, there's a relatively simple relationship among metabolism, body mass, and lifespan. For the most part, as the size of the mammal goes up, its metabolism slows down and its longevity increases. But a new paper (Nature, abstract only, paywalled article) about longevity includes a remarkable statistic: "Nineteen species of mammals live longer than humans, given their body size, of which 18 are bats." Why do bats have such bizarrely long lifespans? (Ars Technica) Meanwhile, in herpetology -- rattlesnakes held in captivity live an average of 15 years. Herpetologist William Brown has spent decades studying a population of timber rattlers in upstate New York, and he's identified two snakes that may about 40 to 50 years old. The Town that Lives with Rattlesnakes (Outside Online)
posted by filthy light thief (23 comments total)

I can access the article; if anyone would like to read it, memail me!
posted by BlackLeotardFront at 10:07 PM on June 12, 2019

I wonder if that had anything to do with their connection to vampires? I had no idea bats actually lived that long.
posted by xammerboy at 10:18 PM on June 12, 2019 [3 favorites]

I've heard of a fanously large infestation of long-lived blood-suckers and reptiles around the state Capitol in Albany. They're not actually native creatures but invasive species; however they refer to themselves as 'elected'.
posted by zaixfeep at 10:33 PM on June 12, 2019 [2 favorites]

(Naked mole rats are the 19th long-living mammal species, in case anyone was wondering.)
posted by Umami Dearest at 10:49 PM on June 12, 2019 [6 favorites]

A bat once flew into my head and knocked me to the ground. I think it was focussed on insects around a light and wasn't expecting a moving large thing walking through its feeding area.

I don't know how old that bat was. I was 19.
posted by hippybear at 10:55 PM on June 12, 2019 [5 favorites]

My friend had the same thing happen to her with a snake. I don't think she was knocked to the ground, but she was pretty unhappy about the whole situation nonetheless.

(Snake fell out of the vines on the Lake Merritt Pergola.)
posted by ryanrs at 11:34 PM on June 12, 2019 [1 favorite]

My general theory is that the less you resemble a prey animal, the longer you live.

In other words, largeness, flight, poison, armor, group living and possibly a few other things correlate with longevity. You obviously can't maximize all of them in the same animal.
posted by Nancy Lebovitz at 12:09 AM on June 13, 2019

largeness, flight, poison, armor, group living and possibly a few other things correlate with longevity. You obviously can't maximize all of them in the same animal.

but Dracula.
posted by Joe in Australia at 1:45 AM on June 13, 2019 [6 favorites]

Also, Manimal.
posted by GenjiandProust at 3:47 AM on June 13, 2019 [1 favorite]

It's cancer that gets us after everything else does, so in one way this research is about anti-cancer defenses. One big-picture hypothesis* is that it's not anti-cancer defenses which cause long life, but instead long life which causes anti-cancer defenses.

Here's how it works: Imagine you're a mouse. You're constantly vulnerable to predators, disease, and starvation. Even if you never get cancer, there's a very high chance you'll die young. A mutation that gives you an additional anti-cancer defense that would extend your maximum lifespan from 3 years to 30 years won't provide you with an evolutionary advantage, because there are so many other things that'll kill you before you turn 2. Another mutation will happen that breaks the first anti-cancer mutation, and it won't make any difference; it'll all just be evolutionary noise. Because you have a short lifespan, you'll end up with a small number of anti-cancer defenses, just the bare minimum needed to get you through a couple of years of life.

But then imagine you're a bat. You fly at night, so birds of prey that depend on their eyesight can't hunt you. You sleep upside down in a cave, so terrestrial predators can't reach you. Some fungal diseases aside, you are very well protected. As long as you don't get cancer, you can live a very long time and have lots of babies. A mutation that gives you an additional anti-cancer defense will be a strong selective advantage. Because you have a long lifespan, you'll end up with a large number of effective anti-cancer defenses, enough to keep you alive and having babies for many years.

Therefore: Long life causes anti-cancer defenses, rather than the other way around.

(This explanation will be more technically accurate if you imagine that you are a population of mice or bats rather than a single mouse or bat.)

*the name of which I can't remember right now, but I'll try to dig it up.
posted by clawsoon at 3:59 AM on June 13, 2019 [5 favorites]

Another thing that plays into this: Large body size is itself a cancer risk, since building a large body requires lots of cell division and every cell division gives a chance for cancer to take off, so distinct tumor suppressor mechanisms evolve in rodent species that differ in size and lifespan. In other words, anything that we learn from bats about cancer might not apply to us, since our large size gives us a different set of cancer problems to deal with.

That large animals should have more cancer but generally don't is known as Peto's Paradox.

A free paper which discusses some of the bat results alongside other cancer research is Mechanisms of cancer resistance in long-lived mammals. It talks a bit more about the hypothesis I mentioned in my previous comment, and gives examples of the kinds of things that protect you from predators and thus promote the evolution of anti-cancer mechanisms: Being big like an elephant or whale; living underground like a naked mole rat; living in a tree like a squirrel (did you know that some squirrels can live 20+ years?); or flying like a bat.
posted by clawsoon at 4:30 AM on June 13, 2019 [2 favorites]

Also, Manimal.

I thought Manimal only had a lifespan of one season.
posted by TedW at 5:00 AM on June 13, 2019 [6 favorites]

In other words, anything that we learn from bats about cancer might not apply to us, since our large size gives us a different set of cancer problems to deal with.

I am probably wrong about that.
posted by clawsoon at 5:54 AM on June 13, 2019

(Naked mole rats are the 19th long-living mammal species, in case anyone was wondering.)

Just conjecture: is there any correlation in mammals between nakedness (lack of fur) and longevity? Think humans, elephants, whales, naked mole rats, hippos. And, there is a naked species of bat.
posted by beagle at 7:06 AM on June 13, 2019

beagle: Just conjecture: is there any correlation in mammals between nakedness (lack of fur) and longevity? Think humans, elephants, whales, naked mole rats, hippos. And, there is a naked species of bat.

I've thought about this, too, and I have a half-baked idea stemming from the hypothesis I talked about above: Fur is a form of protection. If you've developed other forms of self-protection (e.g. living underground, growing really big, building houses), mutations that reduce fur will be neutral and will thus be able to drift through the population, while mutations which promote long life will be positively selected for. In other words, both lack of fur and anti-cancer mechanisms arise from the same root cause, which is that you've figured out some really effective way to protect yourself.

This idea has not been tested at all, and I'm sure that many holes could be poked in it.
posted by clawsoon at 7:48 AM on June 13, 2019 [1 favorite]

I thought Manimal only had a lifespan of one season.
Manimal will live in our hearts forever.
posted by sevenyearlurk at 9:11 AM on June 13, 2019 [1 favorite]

I thought Manimal only had a lifespan of one season.

Manimal didn’t die of old age at the end of the season....
posted by GenjiandProust at 9:15 AM on June 13, 2019

But then imagine you're a bat. Okay.
posted by zaixfeep at 2:49 PM on June 13, 2019

I have a vague recall of reading that a non-trivial driver in evolution is the arms race against parasites.

I speculate that another factor regarding nakedness increasing longevity would be lower parasite load due to less fur for them to burrow into for shelter.
posted by Marticus at 4:23 PM on June 13, 2019

Marticus: I speculate that another factor regarding nakedness increasing longevity would be lower parasite load due to less fur for them to burrow into for shelter.

One challenge with explanations which invoke positive selection rather than neutral drift is that you also have to explain why the vast majority of mammals have kept their fur.
posted by clawsoon at 4:37 PM on June 13, 2019

I always figured its because shit gets cold unless you can rug up in someone else's fur, hide under dirt, or the surface-to-volume ratio helps you out.
posted by Marticus at 4:41 PM on June 13, 2019 [1 favorite]

Tradeoff, makes sense.
posted by clawsoon at 7:58 PM on June 13, 2019

Bats are the only flying mammals, there's a stronger evolutionary pressure for them to weigh less than there is for any other mammal. There's much less evolutionary advantage to decreasing weight for any species that doesn't need to overcome gravity the majority of their waking hours.

There are also species of bats that sleep 18 hours a day, truly worthy of further study.
posted by I paid money to offer this... insight? at 9:49 PM on June 13, 2019