[TimsViv]

There is an interesting link in a new thread in the Lounge - Website Updated! - http://www.dendroboard.com/phpBB2/viewtopic.php?t=3726 -

On the "Dendrobates" page of Evan's link - http://personal.ecu.edu/emt0424/peru04/dendrobates.html - there are pictures of several different morphs of D. Imitator. The interesting thing is, where the D. Imitator's range overlaps with D. ventrimaculatus (Yurimaguas lowlands), the Imitators strongly resemble the vents. However, where the D. Imitator's range overlaps with D. fantasticus (Jeberos), the Imitators strongly resemble the fants.

This begs the question: Is the resemblance due to hybridization of the species or has the D. Imitator evolved to mimic the frogs that it shares territories with?

Hybridization:
Can D. Imitator cross breed with D. Ventrimaculatus and/or D. Fantasticus and produce viable offspring?
If so, what prevents the complete merger of these species into a single morph? Are there audible or visual stimulus that prevent or limit cross breeding?

Mimicry:
If D. Imitator has evolved to mimic the frogs that it shares territories with, what is the advantage of mimicking either of the other species?
Do the other species contain a more efficient toxin that prevents or limits predation?

Also, are the frogs genetically different?

Tim

 

[Scott]

The advantage - mimicing frogs that do have poison in them allows the same prey avoidance that those frogs have (edit: partial points after reading Evan's post).

The Imitators differ genetically from the frogs they are mimicing. I do not know if they can (successfully) hybridize with these species though.

Evan is studying under Kyle Summers and I was at Kyle's IAD talk a couple of years ago.

s

...

Mimicry:
If D. Imitator has evolved to mimic the frogs that it shares territories with, what is the advantage of mimicking either of the other species?
Do the other species contain a more efficient toxin that prevents or limits predation?

Also, are the frogs genetically different?

Tim

 

[Guest]

I would guess that it's mimicry. I think they both could hybridize, however, for mate selection, their calls would easily separate the two. Keep in mind how when many Dendrobatids mate they male continues a short series of calls-- I would think these are species specific. Other than some Hymenoptera/Diptera mimicry, I think Dendrobatids now by far have some of the most interesting and complex mimicry of any animal.
j

 

[Guest]

Perhaps there's a change in either vegetation or predator's territory that selects for the brighter warning colors of intermedius in one area over the other?

 

[Guest]

I can't speak to predators, but from what I hear they are often in stands of Heliconia, which is very difficult to get into. Perhaps, along with many other things, the color is also a deterrant that it's not worth the effort to try to get them. Possibly also the colors could mimic the flowers/seeds of Heliconia (which is less likely), but if you just see a flash or a red, orange, or yellow in a stand of them, it's something I could see being passed off.
j

 

[khoff]

I think Justin is right on with the calls. Our imitators sound nothing like our variabilis. The variabilis sound more like our vents.

 

[Guest]

That was another thing that I just read on his site that blew me away. I've always assumed from the literature that D. variabilis should be included with the D. imitator group (or D. vanzolinii as he states), however, calling them basically a form of D. ventrimaculatus was very interesting. I had them many years ago, and thinking back on that, it does make sense. When they reproduced, I never heard a call, nor even found the tadpoles to see how long they took to morph, but I would now venture that they are roughly the same as D. ventrimaculatus. Very interesting stuff.
j

 

[Guest]

Very nice topic Tim....
Kyle Summers gave a talk about the mimicry of imitator to the surrounding frog at an IAD talk a couple years ago. Have you seen this webpage before? Kyle Summers Mimicry Page

This begs the question: Is the resemblance due to hybridization of the species or has the D. Imitator evolved to mimic the frogs that it shares territories with?

Hybridization:
Can D. Imitator cross breed with D. Ventrimaculatus and/or D. Fantasticus and produce viable offspring?
If so, what prevents the complete merger of these species into a single morph? Are there audible or visual stimulus that prevent or limit cross breeding?

Mimicry:
If D. Imitator has evolved to mimic the frogs that it shares territories with, what is the advantage of mimicking either of the other species?
Do the other species contain a more efficient toxin that prevents or limits predation?

Also, are the frogs genetically different?

Tim

I believe that imitator evolved along side the other species.

While intermedius were once thought to be hybrid from imitator and fantasticus, studies (maybe observations is a better word) of the tadpoles of each species revealed it wasn't. The calls of imitator are a lot different from both vents and fants. They have the nice trill, while fants produce a very quite buzz.
The advantage of mimicking the other species is protection from predation. A predator learns that a frog that looks like a fant. taste bad, so they will stay away from all frogs that look like a fant. So all fants and imitators that look alike have a better chance of living to reproduce, while the imitator that don't will have to be "sampled" to learn the effect. This is known as Mullerian mimicry... (I did a horrible job defining it sorry).

 

[Guest]

The advantage of mimicking the other species is protection from predation. A predator learns that a frog that looks like a fant. taste bad, so they will stay away from all frogs that look like a fant. So all fants and imitators that look alike have a better chance of living to reproduce, while the imitator that don't will have to be "sampled" to learn the effect. This is known as Mullerian mimicry... (I did a horrible job defining it sorry).[/quote]

I have two questions with this. So both of them are toxic enough to avoid predation? I'm not too sure about this-- though admittedly I've never studied their toxins. My other question is what are the predators there? I think this is very important to define so we can have a better idea of what they are trying to fool and why. I would think that there would be a large difference in trying to fool some sort of bird versus a rodent. I've never read of a rodent being a predator of a Dendrobatid, but it would make a lot of sense. I think back on this past summer when Ed Kowalski and I found a ringneck snake that was eaten by some shrew in its burrow. If frogs were attacked by something like that when sleeping, how easy would that be for us to miss? A bit of rambling, but just an idea. I am most interested if anyone can share any insight into predators (if any) in that region.
j

 

[Guest]

So both of them are toxic enough to avoid predation? I'm not too sure about this-- though admittedly I've never studied their toxins.

Well, I don't know the toxin levels of either species, but something has to be pushing them in the same direction, and predation would be the biggest key correct? Now maybe the toxin levels of the imitator are low and the other species have higher levels. That would help explain why the imitator are so diverse. If this is the case the it would be Batesian mimicry. Now maybe the levels of toxin are very low in both, and the pattern of the other frogs works as a better camouflage. I know their is one snake that can handle eating a wild terribilis, or it can withstand ver high levels of the bactrotoxin, so I am sure a the mimicry is predator induced.

This is a very good topic. It is one that make you think..

 

[Guest]

I am most interesting now in finding out the toxicity of pretty much all the species in that region. I do remember hearing of the snake eating the P. terribilis, but I wonder in this region of Peru what is happening with predation (if present). Perhaps there is interspecific competition for habitats, and if by mimicing the more dominant frog the weaker can sneak some of the mating/deposition sites? I don't know, but I am very eager now to see this region this summer. I only hope such exciting things are happening in Ecuador...
j

 

[Guest]

Well maybe I will get lucky and catch a picture of something eating a frog for you, while I am in Peru. Although I don't think I will be there near long enough. Hopefully you will get the time and funding to stay down there longer and figure it out! I am interested in seeing what predators have been documented in trying frog meat.

 

[Guest]

While you are in Ecuador, note the local crab populations for me.
In the Dendrobatidae 3vol book, the author was talking about the crabs that where pretty far inland. He thought they maybe a predator to some of the Pacific populations of Histrionicus.

 

[Guest]

Not a problem, I'll be sure to try to document that.
j

P.S. Someone really should be Brent out of bed for this one...

 

[TimsViv]

I can't speak to predators, but from what I hear they are often in stands of Heliconia, which is very difficult to get into. Perhaps, along with many other things, the color is also a deterrant that it's not worth the effort to try to get them. Possibly also the colors could mimic the flowers/seeds of Heliconia (which is less likely), but if you just see a flash or a red, orange, or yellow in a stand of them, it's something I could see being passed off.
j

BGreen wrote - "Now maybe the levels of toxin are very low in both, and the pattern of the other frogs works as a better camouflage."

I would almost rule out coloration as a way of blending into the habitat, as it was noted that the Imitator were predominately found in areas of Heliconia and the Fantasticus were predominately in the areas of Bromeliads. Both could be found in the region, but each seemed to prefer a specific microhabitat.

Tim

 

[Guest]

P.S. Someone really should be Brent out of bed for this one...

I sent him an email...about 45 mins ago

 

[Ric Sanchez]

To address some of the questions raised in previous posts, variabilis and imitator certainly do not hybridize. They can hybridize (in captivity) but the offpspring are weird and do not seem to be viable. Also, these two frogs are equally toxic. They are Mullerian mimics. This is when 2 toxic species mimic each other to reduce the chances of being eaten by a naive predator. For example, if a naive bird eats an imitator, it will learn not only to avoid imitators but also variabilis. Now the similarities between coloration is not at all due to hybridization, but rather selective pressure to look like the other species. Interestingly, the spectrum of color variation in variabilis was matched by the corresponding populations of imitator. The mimicry motifs change as you move around Peru. The lowland imitators mimic ventrimaculatus, which, according to the most recent molecular phylogeny, is very closely related to variabilis. Imitator also mimics fantasticus, depending on where you are. There is even one spot in the Huallaga canyon where 2 different morphs of imitator are living in sympatry, where each morph is mimicking either fantasticus or ventrimaculatus. The morphs mimicking fantasticus are typically referred to as 'intermedius', while those mimicking vents are the 'yurimaguas', and the highland forms mimicking variabilis are just the regular 'nominat' form. I hope this clears some stuff up!

-Evan

 

[bbrock]

I'm a little swamped today but will read through the whole thread. I'm not sure I have anything to add though. From what I can see, you guys have really covered the issues here. Nicely done!

 

[chuckpowell]

This is a non-starter - they have to be mimics. No way they can be hybrids based on how species are defined. If the frogs interbreed with no barriers to prevent it then they are same species.

On the "Dendrobates" page of Evan's link - http://personal.ecu.edu/emt0424/peru04/dendrobates.html - there are pictures of several different morphs of D. Imitator. The interesting thing is, where the D. Imitator's range overlaps with D. ventrimaculatus (Yurimaguas lowlands), the Imitators strongly resemble the vents. However, where the D. Imitator's range overlaps with D. fantasticus (Jeberos), the Imitators strongly resemble the fants.

This begs the question: Is the resemblance due to hybridization of the species or has the D. Imitator evolved to mimic the frogs that it shares territories with?

Hybridization:
Can D. Imitator cross breed with D. Ventrimaculatus and/or D. Fantasticus and produce viable offspring?
If so, what prevents the complete merger of these species into a single morph? Are there audible or visual stimulus that prevent or limit cross breeding?

Mimicry:
If D. Imitator has evolved to mimic the frogs that it shares territories with, what is the advantage of mimicking either of the other species?
Do the other species contain a more efficient toxin that prevents or limits predation?

Also, are the frogs genetically different?

Tim

 

[bbrock]

This is a non-starter - they have to be mimics. No way they can be hybrids based on how species are defined. If the frogs interbreed with no barriers to prevent it then they are same species.

Your right Chuck but this assumes the classification we are using is correct in the first place. Also, species lines are not always completely distinct. It's possible to have some extremely rare hybridization and still remain seperate species. The no natural interbreeding rule is more of an ideal than a real definition. Dogs have been documented breeding with wild wolves (that's for the frognetters!) but they remain separate species because the amount of genetic exchange from dogs to wild wolves is so miniscule. In other words, barriers (physical or behavioral) are not always impermeable but they may still be sufficient to allow or maintain speciation.

Maybe Evan can shed some light on this but I've felt that these frogs were part of a kind of sloppy species complex meaning they have diverged into distinct species in relatively recent evolutionary history. It seems like not only does this explain the many similarities among these species but also gives them the genetic potential to look variable and like other members of their species. In other words, because the species are related, imitator shares a LOT of genes with all the other species in their range which means that both species can converge to a similar phenotype with selective pressure. What I'm suggesting is that the mimicry may not be entirely a one-way street with imitator molding to form a phenotype that matches another species. The model actually may be having selective pressure toward the mimic as well. After all, the selective advantage is in looking alike. Other selective pressures in the local environment may have created the actual pattern. Or maybe it was just chance.

I'm glad that Evan brought up that imitator are multiple mimics - mimicking different species in different parts of their range. That was the most fascinating part of Kyle's talk at IAD in my opinion. Mullerian mimicry itself is rare enough, but has there ever been documentation of another species mimicking multiple models?

This has also been touched upon but be careful not to think about the avoidance of predation as absolute. If the frogs taste bad enough to gain any significant survival advantage, then the trait is going to be selected for. But the whole mechanism of how Mullerian mimics even form still puzzles me. So you have these two frogs and they both taste like crap so we can assume predators are avoiding both. So what is the selection that makes the frogs converge on a single phenotype? We can all see the advantage once the phenotype has become the same-predators learn to avoid both species with only one bite. So how would they get from point A to point B? Here's one possible scenario is that both species were roughly similar looking but variable in the first place. And the frogs on one end of the spectrum that looked most like their most similar counterparts on the other end got eaten less than other phenotypes. This drives the species closer together in phenotype while leaving imitator still variable enough across its range to do the same thing in a different direction elsewhere. But what kind of predation pressure would it take to do this? I mean, aren't we talking about predators who would avoid either species after learning what they tasted like? So it seems like the pressure to converge would have to come under an already low predation rate which wouldn't be that much pressure at all. In other words, the advantage gained by looking like another toxic species, while real, seems very small compared to just the advantage of being toxic. I don't know if I'm making sense but the numbers are hard to fathom.

Great thread.