Why don't rodents vomit?
March 10, 2015 10:20 AM   Subscribe

A few years ago, it occurred to a few scientists that neither mice or rats are capable of vomiting. What about other rodents? It turns out that being unable to vomit is a trait common to all rodents, not just mice and rats. Interests piqued, the researchers set out to find out why.
posted by sciatrix (49 comments total) 17 users marked this as a favorite
 
Overall the results suggest that the inability to vomit is a general property of Rodentia and that an absent brainstem neurological component is the most likely cause.

"Too dumb to vomit"
posted by Going To Maine at 10:22 AM on March 10, 2015 [13 favorites]


I guess this explains why rat poison is so effective.
posted by maryr at 10:22 AM on March 10, 2015 [10 favorites]


Any word on whether or not we can remove the "brainstem neurological component" from other animals to prevent them from being able to vomit?

I'm thinking about my cat here.
posted by Brackish at 10:27 AM on March 10, 2015 [32 favorites]


Hold up: can we discuss the squirrel-related mountain beaver? This is a thing I had never heard of before. It looks like a woodchuck. They (exclusively?) host the largest known flea. They have slightly opposable thumbs. The male does not have a true scrotum. Wikipedia says it is also called a ground bear, which makes "drop bear" sound like a more valid term than I had previously thought. And wait, what does that make proper bears? Not-ground bears?

In short, what is up with mountain beavers?
posted by maryr at 10:28 AM on March 10, 2015 [17 favorites]


So - the reason my cat constantly stares at squirrels is because she's... jealous?
posted by symbioid at 10:33 AM on March 10, 2015


Horses don't vomit either.
(is curious about other herbivores)

Quail don't puke?


Ah, we had an Ask about it prior

posted by BlueHorse at 10:40 AM on March 10, 2015


Well, I'd love the scientists to tell me what that was that came out of my* squirrel's mouth if it wasn't vomit, after said squirrel was rescued** from choking/getting its mouth stuck shut after I fed it too much straight peanut butter.***

*it technically wasn't mine, but a wild, backyard resident I tamed that eventually became a bit of a neighbourhood pet

**it was rescued by my poor, long-suffering mother who had to massage and pry its mouth open, then force water down its throat

***if you're going to feed peanut butter to squirrels, put it on a cracker (or a cookie), it gives them something to chew and keeps their little mouths from sticking together, lesson learned
posted by sardonyx at 10:46 AM on March 10, 2015 [2 favorites]


"Too dumb to vomit"

One of the Dead Kennedy's early abandoned efforts.
posted by jonmc at 10:52 AM on March 10, 2015 [16 favorites]


Don't we have a lot of studies on the effects of various chemicals on rats/mice and use those to determine how they relate to humans in terms of toxicity and other negative side effects? Does the fact that rats don't vomit affect the results of those studies? Particularly since vomiting is a way in which humans try to expel bad things from our bodies as well as a side effect. I mean, I know a lot of that exposure wasn't done orally, and that vomiting may not have mattered one iota due to the sheer amount of exposure, but is it still something that should have been considered as a factor? Does anybody know?
posted by barchan at 10:54 AM on March 10, 2015 [1 favorite]


I have been battling rats in the basement all winter, and have learned a few fun facts:

1. Their rib cages are flexible enough that an entire rat can squeeze through a hole the size of its skull, which is about the same width as your thumb.
2. They love cat food and Slim Jims more than peanut butter.
3. Their teeth are always growing, so they must chew on stuff to wear their teeth down, and wooden houses are ideal chew toys.
4. They have little body fat and do not regulate their temperature well, so they like living indoors. Mice are even worse at regulating internal temperature and will die if they venture too far from their burrows.
5. They can easily climb vertical surfaces, even metal pipes. They are like Spiderman.
6. They are a lot smarter than you think.
posted by swift at 11:03 AM on March 10, 2015 [7 favorites]


Rabbits, who are Lagomorpha, can't vomit either. It makes hair balls a real danger for them as they groom themselves quite frequently.
posted by tommasz at 11:04 AM on March 10, 2015 [1 favorite]


A few years ago, it occurred to a few scientists that neither mice or rats are capable of vomiting.

This has been known for more than a few years. I know this because as a child I was gifted with a pile of issues of Mad magazine from the early 70's. There was an exchange with a reader in one issue that went something like this:

Reader: "In a previous issue, you depicted a rat vomiting in revulsion. However, rats are unable to vomit; this is one of the reasons why they are so easily controlled with poison."

Mad: "Really? Well, we fed your letter to a bunch of rats and they haven't stopped vomiting yet."
posted by Mayor Curley at 11:05 AM on March 10, 2015 [26 favorites]


Do rats not groom themselves by licking, much like cats do? I would think hairballs would be a deadly problem. The inability to vomit sounds like a bad design flaw.
posted by nicebookrack at 11:09 AM on March 10, 2015


The inability to vomit sounds like a bad design flaw.

Yeah, I'm curious what the tradeoff is, if any. Maybe the ability to vomit would preclude some other anatomical superpower that rats possess.
posted by swift at 11:11 AM on March 10, 2015


My half-assed theory is that, way back, the abiliity to keep really disgusting food down and not starve was more valuable than the ability to survive being poisoned, e.g. by a bad mushroom. Of course, once humans invented rat poison and started leaving other poisonous chemicals around, that might not have been such a good deal.
posted by w0mbat at 11:22 AM on March 10, 2015


The inability to vomit sounds like a bad design flaw.

Always remember that they're not designed. Accidents happen. If they happen near the root of an otherwise successful evolutionary tree, you can have a whole swathe of animals missing something very useful.

All the placenta mammals, for example, are missing an especially efficient DNA repair mechanism that's used by pretty much everything else. The ability to synthesize vitamin C has been lost and gained multiple times. If there are enough other advantages to make up for the loss, the whole package of genes required to Make A Rodent gets carried forward, ability to vomit or not.
posted by clawsoon at 11:29 AM on March 10, 2015 [23 favorites]


Here we conducted behavioral testing of members of all three major groups of Rodentia; mouse-related (rat, mouse, vole, beaver), Ctenohystrica (guinea pig, nutria), and squirrel-related (mountain beaver) species. Prototypical emetic agents, apomorphine (sc), veratrine (sc), and copper sulfate (ig), failed to produce either retching or vomiting in these species (although other behavioral effects, e.g., locomotion, were noted).

Oh, god! That poor grad student!
posted by Naberius at 11:31 AM on March 10, 2015 [1 favorite]


Yeah, I'm curious what the tradeoff is, if any. Maybe the ability to vomit would preclude some other anatomical superpower that rats possess.

I had a long talk with an experienced exterminator last summer when a horde of rats obliterated my tomatoes:

They're intelligent and careful feeders-- they eat small amounts of new substances and if it makes them sick they don't come back to it. This served them well in the eons before the advent of man-made poisons. Modern rat poisons have a very close ratio between a noticeable dose and a lethal one to get around this.

The superpower they got in exchange for not being able to open their stomachs is the very rat-like ability to gorge like a boss. A rat can eat until its gut is absolutely packed and then go a very long time without eating or drinking.
posted by Mayor Curley at 11:33 AM on March 10, 2015 [6 favorites]


Don't we have a lot of studies on the effects of various chemicals on rats/mice and use those to determine how they relate to humans in terms of toxicity and other negative side effects? Does the fact that rats don't vomit affect the results of those studies? Particularly since vomiting is a way in which humans try to expel bad things from our bodies as well as a side effect.

Most animal toxicity studies used to extrapolate to humans look at chronic exposures, which are typically not extreme enough to elicit that kind of response from individual exposures. Regardless, those studies are more interested in what happens once the substance is inside the body, so a test animal vomiting it up wouldn't be very helpful.
posted by C'est la D.C. at 11:34 AM on March 10, 2015 [3 favorites]


I guess this explains why rat poison is so effective.

Yep! No joke. The poison makers don't have to factor in barf limits*, just poison the crap out of them, it'll stay down.

Also: Mice don't sneeze. Learned this from a virologist.

Science, bitches!

*technical term
posted by sidereal at 11:35 AM on March 10, 2015 [1 favorite]


barchan: Don't we have a lot of studies on the effects of various chemicals on rats/mice and use those to determine how they relate to humans in terms of toxicity and other negative side effects? Does the fact that rats don't vomit affect the results of those studies?

I wonder if that's what's covered in, "The implications of these findings for the utility of rodents as models in the area of emesis research are discussed."
posted by clawsoon at 11:36 AM on March 10, 2015 [2 favorites]


Ah! Thanks, C'est la D.C.!
posted by barchan at 11:36 AM on March 10, 2015


And clawsoon, it wasn't. Or at least I didn't see that specifically addressed there or in the discussion. I think C'est la D.C. has it.
posted by barchan at 11:39 AM on March 10, 2015 [1 favorite]


> Quail don't puke?

Status: False.

I never thought it would come up in discussion on the blue, but I have direct personal experience to the contrary, in that I have personally been puked on by a bobwhite quail (Colinus virginianus).

Background: It was a pet. Young self fed the quail copious1 quantities of flour tortilla, which said quail greedily devoured. So greedily, in fact, that it yakked them right back up a few seconds later.

Quibble, if you will, that we may be talking about crop contents rather than stomach contents here. But if it walks like puke and quacks like puke...

(1)-- copious relative to the size of a quail, so maybe ten grams?
posted by sourcequench at 11:44 AM on March 10, 2015 [15 favorites]


MetaFilter: I have personally been puked on by a bobwhite quail.
posted by benito.strauss at 11:46 AM on March 10, 2015 [6 favorites]


the very rat-like ability to gorge like a boss

Excellent metaphor.
posted by JackFlash at 11:49 AM on March 10, 2015 [2 favorites]


Warfarin sodium (Coumadin) is used as a rat poison as it is "It is odorless and tasteless and effective in very low dosages." and causes them to die from internal hemorrhaging (although I was led to believe that it also messes with internal body temperature so the rats/mice go outside to die.

Although I do like to imagine them acting out The Princess Bride:

Rat in black: What you do not smell is called Warfarin powder. It is odorless, tasteless, dissolves instantly in liquid, and is among the more deadlier poisons known to rodentia. All right: where is the poison? The battle of wits has begun. It ends when you decide and we both drink, and find out who is right and who is dead.

Vizzuinea pig: But it's so simple. All I have to do is divine from what I know of you. Are you the sort of rat who would put the poison into his own goblet, or his enemy's? Now, a clever rat would put the poison into his own goblet, because he would know that only a great fool would reach for what he was given. I'm not a great fool, so I can clearly not choose the wine in front of you. But you must have known I was not a great fool; you would have counted on it, so I can clearly not choose the wine in front of me.
posted by plinth at 11:50 AM on March 10, 2015 [2 favorites]


Well now I want to vomit, after reading about the in situ brain-stem preparation. Ewww. Poor grad student, indeed.
posted by domo at 11:51 AM on March 10, 2015


Here's the description:
"Each animal was anesthetized with isoflurane (5%) until the pedal withdrawal reflex was absent. Animals were then transected below the diaphragm and placed into artificial cerebrospinal fluid (ACSF; 5–10°C) composed of the following chemicals: 1.25 mM MgSO4*7H2O, 1.25 mM KH2PO4, 3 mM KCl, 25 mM NaHCO3, 125 mM NaCl, 2.5 mM CaCl2*2H2O.

Following transection, the animal preparation was decerebrated above the superior colliculi. The preparation was placed on a Petri dish containing ACSF cooled over ice. The cerebellum and abdominal cavity organs were removed, keeping the esophagus to the level of the gastroesophageal junction. The diaphragm and part of the lungs were removed to isolate the phrenic nerve for recording. The descending aorta was isolated and the left ribs were removed to prepare for the catheter perfusion. The musk shrew had a larynx denervation in order to prevent sporadic apnea [28]. Lastly, a metal pin was placed between the teeth and the lower jaw, which was later connected to a force transducer to record mouth movements (Fig. 4)."
posted by domo at 11:52 AM on March 10, 2015 [1 favorite]


Fun fact: fossil vomit that is produced by routine vomiting (i.e. the production of gastric pellet kind, like how birds and many other species get rid of indigestible material) is called an emetolite.

The oldest recognized fossil vomit is from the Jurassic. It was produced by an ichthyosaurus, which is not a dinosaur but a large reptile. Sadly, we haven't discovered any dino vomit yet. (Except for of course, Dinosaur Jr.)
posted by barchan at 12:03 PM on March 10, 2015 [2 favorites]


3. Their teeth are always growing, so they must chew on stuff to wear their teeth down
True, false
Rats can wear down their teeth on their own by bruxing. Many other rodents MUST chew or they will end up with serious problem.
Back when I ended up with a few (adorable) pet rats, I was warned to never take my rats to a vet who recommended fasting them before a procedure requiring sedation. The purpose of fasting before a sedative is to reduce the chance of the sedative causing vomiting, but since rats can't vomit, forcing them to fast just causes unnecessary stress on them and a vet who didn't know this obviously isn't particularly familiar with operating on rats.

The More You Know♒★
posted by WaylandSmith at 12:06 PM on March 10, 2015 [9 favorites]


I imagine a couple of rats being tickled (for science) and discussing it later: "Dude, I laughed until I was ready to... well, I don't know, exactly. Something."
posted by Wolfdog at 12:16 PM on March 10, 2015 [4 favorites]




Yeah, I'm curious what the tradeoff is, if any. Maybe the ability to vomit would preclude some other anatomical superpower that rats possess.

In the case of rats, I wonder if the not being able to vomit thing is not so much a tradeoff as just not something that was important enough to be selected for over the many centuries of their evolution. After all, it seems like currently the main utility for vomiting would be in cases of poisoning, and it's probably only been in relatively recent (in the evolutionary sense) times that purposeful poisoning has been used to control rat populations. Who knows, maybe in another couple hundred years, our attempts to exterminate rats will lead to a whole new breed of super rat.*

As for horses, I could definitely see potential advantages to not being able to vomit. The fact that a horse has such a long neck and (I'm assuming) a correspondingly long esophagus could make the mechanics of vomiting quite problematic. Additionally, the fact that they spend so much time with their heads lowered to eat grass/hay would mean that it's very important to have a strong valve keeping food from being regurgitated.

*Is this the right place for an "I for one welcome our new super rat overlord" joke?
posted by litera scripta manet at 12:21 PM on March 10, 2015 [1 favorite]


I guess this explains why rat poison is so effective.

Yep! No joke. The poison makers don't have to factor in barf limits, just poison the crap out of them, it'll stay down.

Also: Mice don't sneeze. Learned this from a virologist.


And that explains why mouse cocaine* is so effective.

 
*aka "muscablow" aka "disney dust" aka . . .
posted by Herodios at 12:23 PM on March 10, 2015 [1 favorite]


posted by potsmokinghippieoverlord at 3:17 PM on March 10 [1 favorite +] [!]

I totally didn't see this when I added that last line in my comment.
posted by litera scripta manet at 12:24 PM on March 10, 2015 [1 favorite]


Regarding mountain beavers, possibly my finest FPP (as far as actually being interesting goes).
posted by maxwelton at 12:32 PM on March 10, 2015 [2 favorites]


I'm going to regret the research my curiosity will force me to do later about why cows vomit/regurgitate/whatever to chew cud and horses don't.
posted by nicebookrack at 12:50 PM on March 10, 2015


I call shenanigans on long-necked horses being unable to vomit while giraffes can regurgitate!
posted by nicebookrack at 12:53 PM on March 10, 2015 [1 favorite]


“The implications of these findings for the utility of rodents as models in the area of emesis research are discussed.”

Emesis research is surely important, and I'm glad I don't do it.
posted by willF at 12:55 PM on March 10, 2015 [3 favorites]


Any word on whether or not we can remove the "brainstem neurological component" from other animals to prevent them from being able to vomit?
I'm thinking about my cat here.


Technically, cats do not usually vomit. Most of what they do is regurgitation. The food has never made it to their stomach.
posted by srboisvert at 1:01 PM on March 10, 2015


I'm going to regret the research my curiosity will force me to do later about why cows vomit/regurgitate/whatever to chew cud and horses don't.

That has to do with the specializations of both herbivores. Cows have really efficient conversion of grass to energy, and the price of that is having a really big, complex, multi-stomached digestive system. The regurgitation to chew cud is part of that. However, having to tote along all that gut weight means cows (and their wild equivalents bison and buffalo) are not particularly good at being fast and getting away from predators that way, and have to rely on defending themselves in other ways. Not all cud-chewers have made this particular trade-off, but the ancestor of cows (the artiodactyls) did fall on the side of "moar digestion infrastructure, less speed."

The ancestors of horses (perissodactyls) opted, far back in their history, to deal with predators by running for it. The cost of that is not being able to cram in so much digestive complexity in the interest of being lightweight, so horses are relatively inefficient and have to eat more to get the same level of energy out of their food than cattle. However, they can run away faster from predators, which is a nice benefit. I'm not sure whether other perissodactyls (rhinos, tapirs) can vomit or not, but I do know that they deal with attempting to derive more efficiency from their diet in other ways. Rabbits (mentioned upthread) can't vomit to chew cud either, for example, increase the efficiency of extracting energy from their grassy diet partially by means of coprophagy--that is, rabbits will frequently eat their food twice. :D

Isn't biology fun?
posted by sciatrix at 1:02 PM on March 10, 2015 [12 favorites]


This study and subsequent ones seem to indicate that mice engage in pica behavior instead of vomiting. Interesting.
posted by willF at 1:06 PM on March 10, 2015


All the placenta mammals, for example, are missing an especially efficient DNA repair mechanism that's used by pretty much everything else. ... If there are enough other advantages to make up for the loss, the whole package of genes required to Make A Rodent gets carried forward, ability to vomit or not.

I also happen to know why this is the case! The DNA repair method in question is an enzyme called photolyase that breaks up a certain kind of DNA damage which is most frequently caused by UV light very efficiently. (It's called photolyase in part because it is also activated by UV light, which has a nice kind of symmetry.) Well, okay--but mammals, especially by the time you evolve placental mammals, are generally coated by a nice dense coat of hair on most of their bodies. That hair blocks UV light pretty effectively, so the UV-specific method of fixing the damage called by UV light wasn't so useful for early placental mammals. So the photolyase genes got broken and lost somewhere in the transition from marsupials to placentals.

(Most species also have another, slightly less efficient but more generalized method of DNA repair that can handle the UV-caused kind of damage, and placental mammals do retain that. Humans, who are relatively highly prone to UV damage because we're a bit hairless, tend to have very nasty outcomes when we have mutations that break this second system of DNA repair. If you want to be grossed out and see the result, google 'xeroderma pigmentosum' sometime.)

So it's not just that if you have other advantages to make up for a loss, you might get selected and evolve forward anyway. It's also the case that if you don't use a trait very much in your biology--or if your ancestors never used it much--there's not too much incentive to keep it around, so it's easy for a broken copy to fix in your ancestors' population.
posted by sciatrix at 1:14 PM on March 10, 2015 [15 favorites]


Sciatrix, that's a fascinating (and sensible) explanation. But do marsupials really have that much less (or less effective) fur?
posted by clawsoon at 2:01 PM on March 10, 2015


Hold up: can we discuss the squirrel-related mountain beaver? This is a thing I had never heard of before. It looks like a woodchuck. They (exclusively?) host the largest known flea.

Re: that flea -- OMFG (NYT)

Rats can wear down their teeth on their own by bruxing. Many other rodents MUST chew or they will end up with serious problem.

I'd bet (OK, not very much) that bruxism, or the lack of it, is a big part of the explanation for the size of that flea: in order for it to efficiently chew on trees and such, the poor mountain beaver's teeth have to stick out so much and mesh in such a way that it can't crush its fleas, and so the fleas face very little selective pressure from biting to be small and elusive.
posted by jamjam at 2:05 PM on March 10, 2015


Very good sciencing, sciatrix, well done!
posted by maryr at 2:37 PM on March 10, 2015 [2 favorites]


Sciatrix, that's a fascinating (and sensible) explanation. But do marsupials really have that much less (or less effective) fur?

Yeah, I was pondering this on the bus ride home myself. Birds also retain photolyase despite the fact that birds have also been pretty feathered for a long time. I don't think I have a definite answer on that one. If I was going to take a stab at it, I would guess that it has to do with one of two things:

1) I'm pretty sure that making photolyase is not particularly energetically expensive. It's a small enzyme as they go, and it's not like you'd ever make too much of it because you can use what you have over and over again. So once you develop a UV-repelling integument--that is, some kind of covering that repels UV without being sensitive to it--maybe then photolyase isn't as critically important as it used to be, but that doesn't necessarily mean you're going to be selected to lose it--it just means that a loss might spread through a population of early placental mammals and fix there, such that none of their descendants have it. That would be a matter of chance, maybe caused by drift in a small population size or just plain luck.

2) My second, less chaos driven hypothesis: it might be to do with sensitive developmental periods. Marsupials generally have to crawl across their mothers' fur to reach their pouches after they're born, right? At this point in their development they are generally hairless (and tiny!), and their mothers are generally moving around and going about their business. And they're exposed to the light for definitely those 5-10 minutes that it takes them (in some species) to get from vagina to pouch, and then possibly (depending on pouch morphology) they might be exposed to light sometimes while gestating in the pouch. I believe the opening to the pouch is, well, open the entire time. It takes quite a while to develop hair completely in marsupials. Similarly, bird chicks--especially those in slower-developing species, often take a while to develop full coats of feathers. (Birds also have naked feet, which might be an issue.) And while those chicks develop their feather coats, they're frequently sitting in reasonably open air nests high in trees.

By contrast, placental mammals often (but not always) are coated in a solid coat of fur by the time they're born, since they do more of that developing inside the definitely-UV-free uterus. Of those species I am aware of which are born hairless and later develop fur, like mice and bears, they tend to be born underground or in a den and not leave that den until they're more developed yet, and there's certainly a shorter window between "born" and "covered in fur" than there is for marsupials. So maybe marsupials don't need photolyase so much as adults, but the costs of getting a UV-induced mutation as developing joeys and not being able to fix it immediately are high enough to make selection sit up and notice changes to the photolyase gene.

All of that is pretty handwavy, though! And I'm not quite sure how you'd test either one. If I had to gamble, I think the first explanation is probably more likely--but the second one is quite a bit of fun!
posted by sciatrix at 3:16 PM on March 10, 2015 [4 favorites]


That's really cool, sciatrix. I like your thinking. *clears paleo throat* There is currently a hypothesis that the loss of that gene is related to the "Nocturnal Bottleneck," when mammals are thought to have been primarily nocturnal for approximately 160 million years. This behavior is thought to have led to several adaptations, including acute hearing, improved sense of smell, brown adipose fat (with some controversy, IIRC, over if marsupials have it?), mitochondria respiration rates, and the loss of UV protection. So the loss of that gene wouldn't have hurt mammals for a very long time due to little actual UV exposure and in that 160 million year interval they had fully developed fur. Although that certainly begs the question of whether or not mammallids became primarily nocturnal due to the loss of the gene, of course.

But when exactly, and why, is not known, or at least I'm not aware of any molecular clockwork done on it, are you? Also unknown is the active selection versus passive as you theorized, which are good possible explanations that I like a lot. Although your comments about skin made me have a thought: could it possibly be related and selected from the split of animals that produce nitrogen waste in the form of urea (cynodonts) and animals that got rid of nitrogen in uric acid (archosaurs)? (Yes, some of these animal groups produce urea today, just talking about their ancestors.) Something about the way skin worked then - archosaurs had skin without any glands in 'em, and are very good at water conservation whereas you need a lot of water you need to produce urea, so maybe there is actually a selection path there. . . .? *Also super handwavy*

Although how we got here from rat no-vomit. . . .hahaha!
posted by barchan at 4:07 PM on March 10, 2015 [6 favorites]


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