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SecretNature t1_itbq089 wrote

The “why” comes down to evolution. Let’s do a thought experiment. There is a population of caterpillars that are poisonous. They look exactly like a non-poisonous species and both are mostly brown. Birds will try to eat both. They notice that some taste great and some taste awful.

Which is which though? You don’t want to make the same mistake twice. There is, of course, genetic variation in coloration. Some of the poisonous caterpillars have small, thin red stripes and some don’t. The birds eat both and notice that all of the ones with red stripes taste bad but only some of the all brown ones taste bad (because some are poisonous and some are the non-poisonous species). They stop eating the striped ones but keep eating the brown ones (and spitting them out). The poisonous ones with no red stripes are thus weeded out of the gene pool and all of the poisonous offspring now only have red stripes. Over time, those red stripes get larger and larger as the caterpillars with bolder red stripes are less likely to accidentally get eaten and thus the genes for bold bright warning colors are more likely to be spread in the gene pool of poisonous animals. The opposite is true for tasty non-poisonous animals. Only those with the best adapted camouflage survive to pass their genes onto the next generation.

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ramriot t1_itbvn7t wrote

This ☝️ is the best answer, most of the others end up being teleological or anthropomorphic arguments.

An interesting since note is that once a boldly coloured hazardous population is present with its selective predators there is often a secondary evolutionary selection for any mutations that leads to other species beginning to resemble it.

Thus the possible evolution of non-stinging Hover Flys with bold black & yellow stripes that closely resemble those on wasps.

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SecretNature t1_itbys04 wrote

Yes, selection can also cause two hazardous species to end up looking like each other as negative interactions with either species is beneficial to both. Monarch butterflies and Viceroy butterflies are an example.

The example you cited with hover flies is Batesian mimicry while the butterfly example is called Müllerian mimicry in case someone wants to learn more.

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ramriot t1_itbzbtb wrote

Thanks for that, just reading through wikipedia on this, I love how the selection pressure is population sensitive. In that if the mimic starts to predominate over the model the whole thing falls apart.

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E_M_E_T t1_itd8osh wrote

I think that's a decent theory but it might have a big problem. If non-poisonous animals start to resemble poisonous ones, then the selection pressure for looking poisonous goes away, as there's only a limited amount of food out there and predators will inevitably realize that some of the colorful prey are tasty as well.

So if the Hover Fly evolution theory is true, then you have to either go with the assumption that food scarcity just isn't enough to push animals back towards older behavior, or you can assume that this trend towards colorful poisonous animals comes and goes in cycles.

Maybe the answer is that Earth's biodiversity reached some kind of equilibrium in the past and the number of new, colorful yet non-poisonous species equals the number of new, poisonous yet colorless species. So the generalization of "colorful animals are poisonous" is always true enough.

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ramriot t1_itdsx9e wrote

Yes, as someone else put it here about Betesian Mimicry the mimic will reach only a minority of the models population because it is becomes dominant the pressure goes away.

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DontWorryImADr t1_itc7g4f wrote

I think the above covers all the good points, so I’ll only add the types:

  • Batesian mimicry is when another organism mimics the warning something else gives without possessing the trait being warned about. Example is a hover fly with black-yellow stripes like stinging insects while possessing no sting.
  • Müllerian mimicry is when multiple species adopt the same warning signal while possessing similar traits. Example is how many stinging insects all utilize black-yellow or similar striping patterns.
  • Mertensian mimicry is similar warnings among deadly and non-deadly threats. Mainly because the warning can’t be learned if every experience is fatal, so the non-deadly are the method of associating the cue with the warning.
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ObviouslyLOL t1_itd1708 wrote

Thanks for adding that. Regarding the Mertensian mimicry, is the non-fatal threat really needed? Whatever predator is eating this prey would also have genetic variations which dictate which foods they go after. Those with a proclivity for eating the fatal prey would die off; those without would pass on that aversion.

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DontWorryImADr t1_itd7uhc wrote

Inherently, you are correct about “the dead don’t breed” and thus it would eventually be conveyed generations down the road to absolutely never touch those things. And in either circumstance, being BRIGHT AND OBVIOUS to potential predators right now is a huge disadvantage. That disadvantage is massive if the trait banks on “the next generation is less likely to eat something like this”. Genetic memory isn’t an ideal value compared to the cost, while showing relevance to a non-deadly warning would be adopted faster. And it benefits the non-deadly variety since both warning routes receive selection pressure. Every event is potentially a usage of defense material (venom), injurious, or fatal, so even snakes with deadly venom are benefitted through avoidance rather than needing to expend the venom.

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lvr- t1_itcxdwg wrote

That does not explain why non poisonous caterpillars does not get more colorful over time

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jysalia t1_itd0riu wrote

The non-poisonous ones that are least flashy and best at hiding are the ones who survive to reproduce. Their offspring will continue to pass down those traits.

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lvr- t1_itd1ebf wrote

This would also be true for poisonous caterpillars, they also could increase their chances to survive if they get or stay inconspicuous (hide better)

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jysalia t1_itd1or3 wrote

But if more of them are surviving because they have visual warnings against being eaten than are surviving because they are good at hiding, those visual warning genes will dominate in the population.

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Ldent t1_itd50uz wrote

This does happen! Sometimes! Small populations or small portions of larger populations will begin looking like their inedible counterparts over time. The problem with this - inedibility isn't a perfect defense. A few inedible individuals will still get eaten and spat out. If the markers that signify inedibility become less reliable (as in, there are greater numbers of edible mimics), then the selection pressures of "don't eat the red striped caterpillars" will weaken, and the selection pressure to be a mimic will as a consequence also weaken. Like parasite - host population trends, this leads to an oscillation between a greater number of mimics and their relative collapse, depending on the specifics of the situation.

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lvr- t1_itd23sy wrote

Yes but we do not have data about that. Also, non poisonous caterpillars could increase their chances of survival if they develop the same flashy pattern as the poisonous ones

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Awkward_Reporter_129 t1_itdevpd wrote

Can you please somehow relate how an octopus may mimic a number of different things in terms of an ecological “language”?

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jabbashotfirst t1_itf6l9v wrote

Wait, but why do all of the ones with red stripes taste poisonous?

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Rather_Dashing t1_ith0fdd wrote

Some developed a poison by chance, and that trait was selected for, as it made predators less likely to eat them.

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Choosyhealer16 t1_ite4qom wrote

Isn't that an example of Natural selection, I learned about it I. 7th grade, had to do with moths if I remember correctly, the brown ones that camoflauged with trees started appearing more than the white ones

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SecretNature t1_itg3jp1 wrote

Yes, it is natural selection. You probably learned about the peppered moth in school. Pretty famous example. https://en.m.wikipedia.org/wiki/Peppered_moth_evolution

Basically the area was so polluted with soot during the industrial revolution that the dark form of the moth was better adapted to survive on the dirty surfaces in town.

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