[Wild Fragaria]

This looks pretty cool to me   

Nature News  Published online: 8 March 2006; | doi:10.1038/news060306-10

Poison mimics go for second best - Imitating the most toxic species around is not a frog's best bet

Imitation may be the sincerest form of flattery, but for some it's about survival.

Animals often avoid predators by copying the appearance of poisonous creatures. Usually the impostor tries to look like the most toxic species around, or imitates a range of toxic animals. But this is not so in the case of Ecuadorian frog Allobates zaparo. This frog chooses to mimic the less toxic of two local species.

"It runs counter to traditional models," says Molly Cummings of the University of Texas, Austin, who describes the frog's strategy in this week's Nature1.

The poison frogs Epipedobates bilinguis and Epipedobates parvulus share a similar warning sign: a bright red back. But the less poisonous and rarer of the two, E. bilinguis, also has yellow markings on its upper arms and thighs.

Cummings found that when A. zaparo was found in the same region as one of these poisonous species, it would imitate that one. But in areas where all three species lived, A. zaparo tended to mimic E. bilinguis.

This is odd. Mimics usually evolve to imitate the more abundant or more toxic species, says Cummings, because that normally guarantees the most protection.

Cummings and her team decided to investigate how the frogs fared in the face of hungry chickens, as a model of natural bird predators. Chickens that were exposed to the very toxic E. parvulus soon learned not to peck them, and avoided any frogs that looked even remotely like the noxious animal.

But chickens that were exposed just to E. bilinguis did not become so wary. They avoided E. bilinguis and any frogs with yellow leg markings, but were not put off all red-backed frogs.

If the mimic had evolved to look like the most toxic creature, it wouldn't have been protected against birds that had met only E. bilinguis, points out Cummings. "This strategy covers all its bases by being protected no matter what species a predator learned on."

The theory may stand up to more scrutiny than previous ideas, says herpetologist John Endler, who works at the University of California, Santa Barbara. The original explanation for why some snakes mimic less toxic cousins, he notes, was that the most dangerous model would end up killing the predator rather than giving it an opportunity to learn. "We now have a more satisfying explanation," he says.

[karajorma]

Interesting. I'm surprised that no one spotted the rather major flaw in the original hypothesis though. If the most toxic animal is so poisonous that attempting to eat it kills the predator then why is it brightly coloured in the first place!

Cummings and her team decided to investigate how the frogs fared in the face of hungry chickens

Not quite certain why but that sentence cracks me up It's almost Pythonesque

John Cleese Dressed up as a Roman Emperor : Throw him to the Lions!
Micheal Palin Dressed up as a roman guard : No lions left. They're all full up from eating the christians
Emperor : Tigers?
Guard : Nope
Emperor : Leopards?
Guard : Nope
Emperor : Wolves?
Guard : Getting some from Germania. Won't be here till next week.
Emperor : Well what do we have?
Guard : Hungry chickens.
Emperor : Hungry CHICKENS!!??....

[Mefustae]

Pythonesque

If that's not a real word, it damn well ought to be!

Edit: Well i'll be damned...

[aldo_14]

Interesting. I'm surprised that no one spotted the rather major flaw in the original hypothesis though. If the most toxic animal is so poisonous that attempting to eat it kills the predator then why is it brightly coloured in the first place!

Wonder if there's a secondary sexual reason (i.e. brightly coloured markings - like a peacocks feathers) that use more natural 'resources' to maintain indicate the sexual attractiveness of the animal (the reason the markings are 'wasteful' ala peacock, is because it makes it hard for less-capable males in particular to mimic them).

[karajorma]

It's possible in some species but in most I think it is just for a warning since the male and female share the same colouration.

[aldo_14]

It's possible in some species but in most I think it is just for a warning since the male and female share the same colouration.

Yep, in all likelihood, albeit couldn't both male and female share the same colouration as a result of inheriting it from the male parent? I think sexual preference can be inherited (i.e. the daughter of a long-tailed swallow is more likely to be attracted to a longer tail), so I'd guess colouration can be, although it is probably the less logical explanation.  Interesting, though, IMO.

[karajorma]

It can be but there would be a selection pressure against it in the case of very toxic animals.

If we're saying that most animals don't realise how toxic this frog because any predator had eaten them (like the original explaination stated) then frogs with the colouration would be more likely to be attacked by predators. There's a fair possibility that even if predator dies as a result that the frog would be badly maimed in the attack. While one sex could have a selection pressure in favour of this (usually males with females doing the picking) I can't see any reason for both sexes to do it since you can only really have one sex selecting a mate. If both tried to compete there would have been an alternative selection pressure in favour of frogs who didn't compete at all, didn't get colourful pigmentation and thus managed to hide from predators better.

All that rests on the original assumption that the animals were too toxic for predators to remember not to eat them of course. If you don't assume that and say that bright colours do discourage predators then it's possible to get bright colours as a result of sexual selection working on top of standard warning colours. Especially if there are several different kinds of predators out there and one or more of them have gained a resistance to the poison.

[aldo_14]

It can be but there would be a selection pressure against it in the case of very toxic animals.

If we're saying that most animals don't realise how toxic this frog because any predator had eaten them (like the original explaination stated) then frogs with the colouration would be more likely to be attacked by predators. There's a fair possibility that even if predator dies as a result that the frog would be badly maimed in the attack. While one sex could have a selection pressure in favour of this (usually males with females doing the picking) I can't see any reason for both sexes to do it since you can only really have one sex selecting a mate. If both tried to compete there would have been an alternative selection pressure in favour of frogs who didn't compete at all, didn't get colourful pigmentation and thus managed to hide from predators better.

All that rests on the original assumption that the animals were too toxic for predators to remember not to eat them of course. If you don't assume that and say that bright colours do discourage predators then it's possible to get bright colours as a result of sexual selection working on top of standard warning colours. Especially if there are several different kinds of predators out there and one or more of them have gained a resistance to the poison.

I was thinking more along the lines that the colouration could have a dual purpose, either in that it started as sexual ornamentation but then spread as 'warning' markings, or that is started as warning markings but became adapted by the male side as a display characteristic (say, how bright the pigmentation is).  As an abstract thought, anyways.

[karajorma]

Wouldn't disagree with that possibility

[Wild Fragaria]

Haven't posted much in the last few days because I was out sick.  But I like what you guys pointed out and certainly think that they are pretty interesting speculations