How did the Booze-Rat evolve its defensive mechanism?

Question

In a specialised organ, the Vesica Spirite, which in function and makeup resembles a cross between the Ventriculus and the Vesica Biliaris, the animal creates and stores potent spirits by the means of a symbiology with a species of Saccharomycetales so far only found in that location.

Excerpt from Hjårdan Animaliæ

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Welcome to the Most Ingenious Questions You Never Thought Of. Today we look at the booze-rat, again. An animal aptly named for its unique defensive mechanism of storing potent alcohol in its body in order to daze/incapacitate a predator.

As mentioned in the excerpt from the widely known book Hjårdan Animaliæ, the booze-rat has a specialized organ called the Vesica Spirite, we'll call it the booze-bladder. The booze-bladder is home to a specialized strand of yeast that turn sugars into potent alcohol. In order to prevent the alcohol from seeping into the bloodstream unwanted, the booze-bladder is lined with a thick layer of mucus.

If a colony is attacked/goes hunting, the rats that get attacked by the predator will release the alcohol stored in their body into their stomach. The induction of the potent alcohols into the stomach will trigger a disequilibrium, causing the booze-rat to expulse its gastric contents thus covering itself with the dangerous liquid.

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Q: How did the booze-rat evolve into the being described above?

This question is asking for a description of how the booze-rat has evolved into its current form. It does not necessarily ask for a detailed account back to the first multi-cell-organism but it does ask for more than a simple because things answer.

The term booze-rat has been chosen because it sounds rad. The animal in question does not necessarily have to be an actual rat - the animal is meant to be a rodent though.

Answer 1

First, let us examine what makes rodents so successful.

Rats are amazingly versatile creatures, able to adapt to almost any environment they enter; this ability is derived from their sophisticated array of highly-attuned senses of touch and smell as well as their no-fuss approach to food (consuming practically anything from grains and fruit to meat and rotting scraps - the definition of easy-to-please). In addition to these characteristics, rats have an intelligence that rivals most animals of their size, giving them superior advantage when it comes to avoiding danger (or in the booze-rats case, taking it on) and successfully colonising a new area.

Even with such impressive skills, how have rats managed to appear practically everywhere on earth so quickly? The answer: Us.

Humanities excessive desire to expand our reign has seen the rapid evolution of transport; trains, planes, automobiles, rocket-ships, great oceanic freighters - they all have given man the ability to travel with a speed and effectiveness beyond belief; but this achievement would never just be for us, for many other creatures (cough -rats) too dreamt of seeing the world too, and we gave them the ultimate means to do so.

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So how has the booze-rat evolved to it's present majesty?

Our story begins thousands of years ago with the first explorers. At this time in history, most towns and cities were squat and overcrowded, the perfect breeding grounds for vermin of all sorts - namely the black and brown rats. These pesky critters happily co-existed with humans, sharing their germs and fleas, but they soon began to feel unwanted, so as the sailors boarded their shiny new ships and set off in search of new lands, they did too.

The vessels dark bowels with their vast stores of grain and rum were ideal sanctuaries, allowing for the rodents to simply sit back and relax and breed and do whatever else happy rodents do; at each new port, the more curious creatures would disembark whilst the others hung back to sample whatever strange delicacies the sailors brought back onboard, like spices and bananas and copious amounts of tobacco and wine. These are our primary evolvutionaries.

Whilst the fruits were easily ingested by the rats, who were growing larger and more comfortable in their surrounds, the latter had a profound effect on the few that dare drink it. Becoming groggy and disorientated, many died in the hours following; but a few hearty critters lived to drink another day, breeding to create more alcohol tolerant generations.

Ship Captains soon began to notice the un-welcomed stowaways, deciding to recruit dockyard cats as a means of pest control. This worked out surprisingly well for those felines who could withstand the oceans unpredictable swell, getting a regular and hearty feed off the vermin.

One day though, one of these cats came across a group of new generation rats who had bathed in the contents of a ruptured wine cask. Having no chance at escape in their intoxicated state, they was quickly devoured, the cat falling into a drunken stupor from their booze-soaked fur. Now incapacitated and reeking of death, the other rats moved in (not the sort of creatures to shy away from an easy meal…) In the hours that followed, as much as the cat tried to fend away the creatures who nipped and swarmed, it was overwhelmed and eaten with prejudice. It became the first time prey had killed predator on the high seas, all because of the sacrifice of a few drunk rats...

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From here, we fast-track our story 500 years.

Sea trade was booming; many thousands of the evolutionary rat generations have been and gone, the vermin having evolved to better withstand the alcoholic wares of the rum/wine barrels beneath deck, becoming confident enough to stand up to any small predator that came their way, having realised that by soaking themselves in booze, anything that ate them would become easy pickings for the remaining rats.

With each ship landing, more and more of these evolved rodents made their way off-deck and into new worlds, most lush with vegetation, sporting impressive vineyards and distilleries... The bigger more powerful rodent quickly overpowered any rival inhabitants, coming to dominate the environment in the space of weeks. They took residency in the vineyard and jungles, feasting on all they had to offer, regularly indulging in grapes and pawpaw and mango, fresh or fermenting, growing ever more tolerant to the effects of the alcohol produced by the various microbes on each. They evolve a partitioned stomach to separate ethanol from the nutritious fruit pulp; this waste was excreted quickly to avoid serious organ damage.

They were still subject to predatory activity and, without the safety of the ships strong alcohol, were unable to defend their nests to the extent they originally could, so rats began to "spray" one another with the excreted ethanol in a bid to replicate the effects of the wine-bathing and protect themselves.

Forward another 500 years...

The evolutionary rats have become fully adapted to their new world environments, the vineyard/jungle dwellers thriving greatly.

The rats no longer need to spray one another; their partitioned stomach has since separated into a separate organ capable of storing larger amounts of ethanol safely (the organ walls covered by a thick mucus) that can be excreted in much the same way if it becomes too full. It is called a booze-bladder.

Predators still threaten the rats, who now possess a more specialised means of protection that better resembles the original wine-bathing. Once a predator is spotted, the older rats leave their nest to confront it, mixing the contents of their stomach and booze-bladder once attacked, causing it to regurgitate the strong ethanol over itself ("bathing") in preparation of being eaten. It's sacrifice allows for the rest of the rat colony to attack the intoxicated predator in the knowledge that due to the brave rodents actions, they will eat as kings.

Answer 2

Harry David posted this, clearly explaining that rats can't vomit. They lack the required neurology and muscle coordination to overcome their esophageal sphincter, and expel stomach contents through the mouth. They have instead evolved a sophisticated avoidance measure, by only eating small amounts of new food. If it makes them sick they'll use a keen sense of smell and taste to never eat it again. And it appears to be true of all rodents. Therefore, whatever the evolutionary cause of this is, it must predate the modern differentiation of rodents to a common ancestor. This effectively means changing the way rodents evolved outright, which doesn't really fit I'd argue since they would no longer be rodents surely.

Hopefully I wont bore anyone with taxonomical classifications, rodents are part of the Rodentia order who's earliest known fossils come from the Laurasian supercontinent some 66million years ago (yeah they're really old).
Sadly this makes them a rather different animal from the skunk or zorilla as those are part of the Carnivora family. Their fossil record seems to start about 42 million years ago.

However, there exists a simple fix to still want to call the animal a booze rat, and that is its colloquial name. I would strongly suggest though that this animal be part of the Mephitis (skunk) family. From there its anal sac's rather secrete an ethanol based substance (Mephitis Ethanolus, see what I did there).
A good example of taxonomical errors like this is the African striped skunk (AKA the zorilla), which is in fact not a skunk at all, but is more closely related to the African weasel. It is thus not part of the Mephitis classification.

Now you have an ethanol skunk known as a 'Booze Rat'. If you've ever drunk 80-100% alcohol you'll know it burns, and would irritate the eyes and nose. How intoxicating a few milliliters would actually be is debatable, but it may be enough to ward off predators. Rather than anal glands the animal could have glands elsewhere like the Slow Loris, where the glands are located on the elbows. This would allow the the Booze Rat to cover itself, especially if the glands were around the neck. It could the spray backwards covering itself.
Anal sacs make more sense though since all Carnivora species have these sacs. The booze rat name could then come from a rat/weasel appearance and the fact that people catch the rats and use their sprays to get drunk. Yeah that grossed me out just typing it.

Answer 3

Once upon a time there was a rat with a yeast infection and a bit of a dicky tummy.

He wasn't particularly sick and managed to stay in good condition. Though he had to eat and drink a bit more to keep himself going day to day, he still survived when the dogs came through. Initially as his infection passed around the group some died, but some survived. Those who recovered from the infection remained ordinary rats. Some like him who neither recovered nor died, averaged better outcomes from close encounters with predators, they lived slightly longer, had more young. They passed the infection on in turn to their young, who also adapted to live with it, slightly better than their parents had.

It's something that ultimately has to be actively selected for to be passed on. Rats have very fast generations, a beneficial adaptation could be passed rapidly to a large percentage of the next generation. Something like this that is primarily beneficial for dealing with predators, would help a group near the peak of the predator curve on the predator-prey population graph.

Answer 4

There is a multistage but logical process by which the Booze rats evolve alongside their favorite food and their archrivals.

There is a plant and an early mammal. For all intents and purposes, the consumption of the plant at early stages by the mammal keeps the population of the plant in check.

1: The plant develops a toxin which prevents the mammals from eating it during the reproductive process. It starting in the seeds but eventually develops in the sprouts, unripe fruits, and young plants. Older plants and ripe fruits are non-toxic. This food shortage causes the species to diverge into two mammals. The strong proto-cats eat the high caloric fruits of the plant during the summer, the best parts of the body in the fall, and the proto-booze-rats during the winter and fall. The proto-booze-rats become scavengers and adopt a diet which consists of low caloric food scraps from the body of the plant or the discarded parts of their siblings. These crappy foods have high cellulose or hard to breakdown protein content so, a second, high-pH stomach is evolved to allow a specialized bacteria to help breakdown these foods before the main stomach. Multi-stomached herbivores are actually quite common.

2: An initially parasitic yeast begins to infect this bladder converting sugars to alcohol. To combat this, the rats learn to metabolize alcohol, additional mucus forms to reduce absorption through stomach walls, and the initial bacteria become more resistant. If the alcohol concentration gets too high, they learn to regurgitate to preserve the symbiotic relationship with the cellulose digesting bacteria.

3: The booze-rats realize they can eat the plant when it is toxic now. Fermination in their alcohol bladder (again their first stomach) causes the toxin to breakdown. Their diet changes because they now have a high caloric food that is poisonous to the cats. This diet quickly kills off the cellulose eating bacteria but at a very quick rate (for evolution) the rats stop regurgitating at low to moderate alcohol concentrations, dramatically increase alcohol metabolism, and their bladders increase in size as the fermentation becomes desirable.

4: A cyclic pattern occurs which is very favorable for rapid evolution. The rat population booms as they eat their seemingly infinite food source. The cat population booms as they eat the rats. The plant population dwindles as they can't reproduce. Most of the rats die off from predation and from starvation. Most of the cats die of starvation. The plant population booms as it reproduces quickly with low rat population. We repeat. Only the most toxic plants survive as the rats know not to eat them so they rapidly become more toxic. The cats evolve to become successful exclusive carnivores. The rats evolve to be able to handle more and more toxic plant material by storing more and more alcohol in their stomach. The rats retain their omnivore classification as they become cannibalistic during food shortages.

4: The rats learn to vomit again. Whether from the toxin or the alcohol, the fluid in the stomach of the rats is so strong the rats learn they can incapacitate and/or kill the cats by vomiting on them. The cat population decreases in a time of ample plant material but this backfires. Rats feed on the seeds which were once left alone so the level of toxins in the bladder become more fatal. The toxic plant population stops having an evolutionary imperative to become more toxic and, instead, becomes less toxic over time as the most toxic plants are targeted for consumption. Only the strongest, stealthiest, and fastest cats can avoid being incapacitated.

So: The now fully evolved booze-rats feed on the fruit of a relatively non-toxic plant that relies on rapid reproduction and growth to survive. They store a large portion of this in their first stomach to allow it to ferment. They defend themselves from the carnivorous cat creatures by vomiting this alcohol on them but it is less effective than it used to be.

TLDR: Second stomach forms to digest cellulose. It becomes alcohollic due to infection. Infection turns out to be benefit as fermentation breaks down poisonous food. Evolve to have high tolerance for alcohol and poison. Evolve to vomit poison and alcohol to protect self. Poison plant dies off but alcohol vomit is still useful.

Answer 5

Most likely it didn't, it is probably genetically engineered

Alcohol has a very strong smell and taste, as it is highly volatile. Predators typically possess a keen sense of smell. They should quickly learn to simply avoid the booze rat - just like they learn to avoid eating anything poisonous. Even if they for some reason can't sense alcohol - because their scent receptors don't respond to it - they would still learn what a booze rat looks like, and simply would not hunt it.

If they haven't, and the booze-trap still works, it means that the introduction of booze generation into the rat's body was very sudden, and very recent.

Answer 6

They get it from their food

You don't really need a booze-bladder. A lot of animals pick up toxins from their food, and end up storing them in their body. Some animals do this unintentionally, like sea lampreys and poisonous heavy metals, and some do it intentionally, like poison dart frogs and monach butterflies.

The pen-tailed tree shrew (Ptilocercus lowii) spends almost every night feeding on the highly fermented nectar of the bertam palm, consuming the equivalent of about 10 to 12 glasses of red wine per night. Every night. They eat other things like insects, fruit, and geckos, but they drink a lot of fermented nectar. And never get drunk.

So, you can get a scenario where your ancestral booze rat starts eating a highly fermented food item, mostly because it tastes good and is high in sugar, and over generations its metabolism begins to evolve to tolerate higher concentrations of alcohol in its system. Until you get booze rats who are basically walking around with a blood-alcohol level that would knock any other animal flat on its back. Predators that eat the booze rat end up getting so sick and drunk they usually don't survive, and predators that survive eating a booze rat once usually don't repeat the act.

And maybe the booze rat starts harboring fermenting bacteria from the food it eats in chambers of its gut similar to a ruminating mammal. And when a predator goes to eat one the booze-rat upchucks its last meal of highly fermented foul-smelling food into the predator's face, at the same time splattering it all over the booze rat both putting the predator off its meal and making the booze rat look and smell awful, in the same way that an opossum playing dead starts drooling and leaking foul-smelling fluid from its anal glands to make a predator too grossed out to eat it.

People have taken to making twice-fermented alcoholic beverages out of booze rat vomit. Because of course they do.