Surviving exhibitionism and the art of communication. An ASAB Education resource by Dr. Nicola Marples School of Natural Sciences, Trinity College Dublin. Most edible animals are cryptic (or camouflaged). But some are brightly coloured and obvious.
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Surviving exhibitionism and
the art of communication
An ASAB Education resource by
Dr. Nicola Marples
School of Natural Sciences, Trinity College Dublin
Most edible animals are cryptic (or camouflaged).
But some are brightly coloured and obvious.
Cryptic animals and plants are protected from predators because they are hard to find.
But brightly coloured animals are easy to spot, so they are in danger from predators who can easily find and eat them.
To protect themselves, brightly coloured animals contain toxins (poisons) which make the predator sick if they eat them.
They may get the toxins from their food.
This is called sequestering toxins
Here is a caterpillar of the monarch butterfly sequestering a heart poison from the milkweed plant
Here is a sea slug who collects poison from the jellyfish it eats, making it toxic to fish who would otherwise eat it.
This snake collects poisons from a toxic toad which it eats. It stores the toxins in the yellow area on its neck.
If they don’t eat anything poisonous, they have to make their own poison by special chemical processes in their body called chemical synthesis.
Wasps synthesise the poison in their sting
And dart poison frogs synthesise a toxin so poisonous that one lick of their skin would kill you!
For the predator to learn about it, the toxic animal will be attacked.
This is not good for the victim’s survival!
But most toxins are inside the animal.
Why might that be a problem?
(Think before you click!)
This butterfly has had its wings bitten by a bird!
Skunks do this
To avoid this, the toxic animal can spray the toxin at its predator.
So do ants
And bombardier beetles fire boiling acid it at their enemies!
Or the brightly coloured animals can use a different tactic. They signal to the predators that they are toxic.
These animals which are both brightly coloured and contain a toxin, are called aposematic animals. Another name for them is warningly coloured.
Aposematic animals use colours like:
Red and yellow with black stripes or spots to signal their toxicity.
We use the same colours to signal danger:
Their bright, recognisable patterns let the predators learn easily that animals with those colours are nasty to eat.
Their signals have evolved to make it easy for the predator to learn.
But what makes a signal easy to learn?
Think about how you would teach a dog to sit.
You use simple, fairly loud, clear commands.
You repeat them over and over.
You reward him if he does sit, every time he does it.
Your reward is given quickly after he sits.
You may use a hand signal at the same time you say “sit”.
Each of the factors in the left hand list are being used by the method on the right.
But aposematic animals don’t limit their signals to colour; they also signal to the predators with smells, taste, and sounds.
Ladybirds produce blood from their joints.
This “reflex blood” tastes very bitter, and has a weird smell called pyrazine.
Bees buzz a characteristic warning sound
Some cockroaches hiss in warning
Rattlesnakes rattle their tails
Can you think of any other warning sounds, smells or tastes?
Does it really help the predator learn if the prey has several types of signal at once?
Wouldn’t it just confuse the predator?
Meet Emma Siddall, who has been doing experiments to find out.
Emma used chicks as a predator, and the prey “insects” were crumbs of coloured chick food.
The chick food was dyed yellow or green, and the yellow crumbs made nasty with a bitter chemical called “bitrex”
She wanted to test whether the chicks could learn to avoid the yellow crumbs and only eat the green ones.
The single green or yellow crumbs were offered to the chicks in holes round the edge of a tray. A second signal, a smell, could be put beneath each yellow crumb in a special chamber below each hole.
She used pyrazine as the odour, which is what ladybirds smell of.
So the chicks were given two signals: yellow colour, and a warning smell. They walked around the tray choosing what to eat.
Did having two signals help the chicks learn to avoid the yellow crumbs?
Here you can see the number of crumbs eaten in each trial. The chicks all ate a lot of yellow crumbs in the first trial, but those with the pyrazine odour learned quickly to avoid the yellow crumbs. Those with only one signal, the yellow colour, learned more slowly and ate more yellow crumbs in all.
So an insect with two cues, odour and colour, will probably be better at teaching the birds to avoid it than an insect which has only one part to its signal, colour alone.
So at least one aspect of aposematic signals has evolved to aid learning.
What about the other factors which aid learning? Do aposematic animals show them too?
In each of the following slides you need to decide which of the factors which aid learning are definitely being used by the aposematic animal pictured. If you don’t know enough about the animal (maybe no-one does) then don’t count that factor for that animal.
These are toxic striped ladybirds which smell of pyrazine and taste horrible. They often aggregate together like this.
Each spine on this lionfish can give you a very painful sting!
This is a very venomous coral snake. A bite would kill a man within hours.
This is a milk snake. It is totally harmless, but copies the signal of the coral snake, giving a visual signal which is a lie!
So cheats on the signaling system exist. They are called Batesian Mimics, and they make the signal harder to learn.
Here are some other Batesian mimics to finish with, all of which are harmless, but look just like a toxic species. See if you can think of any more!
The top frog is harmless, the bottom two species are deadly!