How does an animal bred to be a bioindicator function?

Question

You're probably familiar with the use of canary during coal mining. At the slightest trace of poisonous gas the canary dies and the miners are warned. Well my story involves a small animal that was bred over the course of thousands of years to serve as a living bioindicator. The animal is highly sensitive to changes in the environment and gives off different signals to tell the humans what the environment is like. Is it too hot, cold, dry, humid, acidic or basic? The animal accurately displays all of these. Or just dies, in which case they reproduce quick enough to be replaceable. The animal is basically a sacrificial pet. It serves as a food taster, anything it can eat we can eat.

The thing is pretty much living litmus paper, giving off changes in colour or other signals. What I haven't got figured out though is how the thing gives off overlapping signals for different stimuli. For example if its hot and dry, the signal would be different from when it's hot and wet. Or when the ph of the ground is too high how do you know it's not a bacterial infection? The creatures form changes depending on where it lives, so would it have distinct signals to display everything at once?

It has to be visual, physical changes, otherwise if the creature dies there's no telling what was wrong.

Edit: [To be more specific the critter displays temperature, humidity, Ph as well as the presence of bacteria and pollutants.]

Answer 1

Changing physicality

There are many ways that these things can be shown. Even just for temperature we have all these nifty little things that can show the temperature via buoyancy or a changing colour.

The creature can do much of the same. Sticking with temperature, change colours on demand like a chameleon, or change colours thanks to reversible natural processes of chemicals/materials.

But colour isn't the only thing we can communicate. Texture and excretion for example. How to tell if someone is hot or cold? Goosebumps or sweat. That is temperature again, but many creatures have ways that display how wet they are. The wetter the more smooth their fur. If dry or drying, they get more ruffled.

With a lot context also matters. A grin can mean happiness or discomfort. Sweat can come from fear or heat. Redness of the skin can come from too hot, cold, too much rubbing on skin, shyness and sex. For each you can often determine the causes of these results by context.

In addition, different areas can mean different things. Grey hairs in a beard are less related to age then hairs on top of the heat. Sweating is done in some areas more then others, so dry skin doesn't mean it isn't hot enough to sweat.

We can continue with multiple things like this, but let's just make a short list.

• Temperature - colour of the creature
• Wet/dry air - texture of fur/skin/feathers
• Submerged/on land - slight different texture of the fur/skin/feathers
• PH - colour fur/skin/hair on top of the ends of appendages
• bad food - smell (humans do that too, believe me)
• bacteria or sickness - sound

Many of these can also have overlapping categories of indicators. Like happiness can be both a smile and an accompanying sound, so can you do temperature with colour and particular smells, very different from the smells and colour of food poisoning.

It seems to me more a matter of how you want it, then how it should be.

Answer 2

A Monkey

Simians have a wide array of facial expressions^{[citation needed]}. They can be trained to show their teeth when cold, put their tongue out when hot, bite their lips when it is too dry etc.

If the monkey in question is a hairless one, such as a Homo sapiens, you may need no training at all. They sweat when it is hot^{[citation needed]}, go pale when it is cold^{[citation needed]}, start losing pieces of skin when it is too acidic^{[citation needed]} etc. Adult ones tend to be less sensitive to weather conditions, so you may tune the sensitivity to stimuli by choosing younger or older individuals.

Or when the ph of the ground is too high how do you know it's not a bacterial infection?

Bacterial infections have an incubation period of a few days before they display symptoms. Viral infections too. Regular blood testing will solve your problem - check white blood cell counts.

It serves as a food taster, anything it can eat we can eat.

Humans can generally eat the same food that humans can eat^{[citation needed]}.

Answer 3

Changing colonies of microorganisms.

Your detector is a mixed colony of micro-organisms. They grow fast, when they can grow. The colonies that appear and what they do to the substrate tells you about the conditions you are in.

AN example: mannitol salt agar.

https://en.wikipedia.org/wiki/Mannitol_salt_agar

This is salty agar. A lot of bacteria cant tolerate the salt and dont grow. Micrococcus did not grow. Certain gram positive organisms can. The agar also has mannitol. Staph aureus can ferment mannitol and turns the indicator yellow. Staph epidermidis can grow but they don't ferment mannitol so the agar stays pink.

Your dishes have various micro-organisms. Ambient conditions where you are affect the growth medium in such a way as to favor certain organisms and inhibit others. When you thaw the dish (or hydrate it) and start things growing, you get your readout in a day.

Suppose there was a yeast in there. If it is basic or neutral I will see their white colonies. If it is acidic there will be less and there will be smaller. If it is really acidic the yeast will not be present. I can estimate acidity by the appearance of the yeast colonies if any. Each organism will have a characteristic appearance as a colony and the gestalt as regards size and number of colonies will translate into the readout for your area.

It is not as fast as a dying canary but maybe more versatile. And not pure sci fi!