Do chevron tangs mimic potter's angels????

[Anonymous]

I just sent this email to coralrealm.com

"Hi,
This one's for Scott, I guess. I've always been fascinated by the Batesian mimicry of mimic tangs and how similar they look to their pygmy angel counterparts. Well, when I was looking at a juvenile Chevron tang and a Potter's angel, it kind of struck me how similar their coloration/markings are, and that their ranges are pretty close to the same. From what I've read, the tangs only look like that as juvies, and change as adults. Granted, they aren't as good a mimic as the others, but could the chevron's be in the early stages of evolving mimicry of the angel?"

Whaddya guys think?

 

[Desolas]

That's an interesting theory, the first thing that popped into my head, which is probably an ignorant statement would be; are they located near one another in the wild? I would think that would be the first prerequisite for any mimicking to happen.

They do look pretty similar, I have never noticed that.. Which is odd since I've always admired both fish and wished I could keep them. It will be interesting to see Scott's response.

Wes

 

[Anonymous]

Wes, good question, and it provides even more evidence for the possibility--they are both found only in Hawaii.

Another prerequisite is that the mimicked species is much more common than the mimicker...I don't know if that's true or not in this case.

 

[Gary Majchrzak]

Here's a couple more questions for Scott: how is 'Reef Fishes, vol.II' coming along, and why are so many fish in Hawaiian waters named after Potter? Another Hawaiian endemic- Potter's Leopard Wrasse {Macropharyngodon geoffroyi} also has similar markings to the aforementioned fishes. {See pic of the Wrasse in link.}

http://www.fishbase.org/Summary/Species ... e=geoffroy

 

[Anonymous]

Heh, good point, I hadn't ever even seen that wrasse. It defintely has that same orange to blue coloration, with random spots.

"The naming of this fish honors the memory of Mr. Frederick A. Potter (1874-1961), who served from 1903 to 1940 as the first Director of the Waikiki Aquarium."

I'm wondering how both a fish and a coral, Trachyphyliia geoffroyi, both got named after the same person....

 

[Markv]

I've wondered this myself many times. Another point to make this case is that the Chevron tangs only exhibit this coloration as juveniles. As adults, they support a drab coloration. Most of the other tang mimics display mimic colors only as juveniles as well. For example, the tang that mimics the lemonpeel angel, Acanthurus pyroferus.

 

[John_Brandt]

I think we need to talk about this one some more.

I'm not so sure that the Chevron tang really does mimic the Potter's angel. If it does, it is doing a crummy job compared to the true Mimic tangs (Acanthurus pyroferus & tristis).

The Chevron only sorta looks like the Potter's. The closer you look the worse the mimicry is. The Potter's has defined vertical squiggly lines while the Chevron has randomish squiggly lines that approximate a chevron in their overall pattern, but with a horizontal bias. The angel also has a center body shading (that is sometimes very dark) that is completely missing in the tang. The tang has a very dark top and bottom but the angel really doesn't. The angel's tail is dark, but the tang's isn't. The angel's finnage is more rounded while the tang's fins taper off. It's a crappy mimic when you compare it to the almost ridiculous perfection of the true Mimic tangs.

Further, the geographic range of the Chevron tang is fairly widespread (though I think it is uncommon everywhere) while the Potter's angel is restricted to Hawaii. The Chevron looks the same everywhere it's found. IOW, if the tang is mimicking the angel, it is doing so even many thousands of miles away from where the angels are found. The Mimic tangs however, mimic the Centropyge angels that they live with.

Classic Batesian mimicry proposes that if you can look like something dangerous or toxic, animals will avoid you that would otherwise eat you. But it seems that mimicry can get you more benefits than just that, and the tang mimicry may have multiple benefits.

By not looking like adult tangs, the juveniles might avoid territorial conflicts with adults and therefore live amongst them 'unnoticed'. But that would suggest that juvenile tangs would be able to look like anything other than an adult to avoid this conflict. So why look like an angel?

By looking like an angelfish, the tang might avoid some of the relentless aggressive protection of algae done by damsels. Damsels hate tangs with a passion because tangs are out to eat their precious algae patch that they guard violently. The angels might be more tolerated by the damsels, allowing the juvenile tang to avoid this aggression until it gets large enough to deal with it.

It may be that the juvenile tangs avoid being eaten by predators because they look like an angelfish. It's been proposed that this might be because the angels have cheek spines that they can erect and use in defense. The spines might create such a hassle for fish trying to swallow an angel that they just avoid them entirely. But the tang has erectile spines (bladelike) of its own at the base of the tail.

Maybe Centropyge angels are mimicking juvenile tangs :wink:

I will say the same about the wrasse. It's color only approximates the angel. There is no shading with the wrasse and it's another crappy attempt if it really is one. Ichthyologists have not mentioned it mimicking the angel (nor have they mentioned the Chevron mimicking the angel) and they also do not call it a Potter's Wrasse. AFAIK, only certain people in the aquarium trade call this wrasse a Potter's wrasse. It's not even listed as one of the known common names in FishBase.

Maybe the mimicry is good enough to work even as crude as it is. But it still would beg the question of why the true Mimic tangs are a perfect replica of the Centropyge angels, if crudeness will work.

There was a good earlier thread on the Mimic tangs here: http://reefs.org/phpBB2/viewtopic.php?t=35313

 

[Anonymous]

John, of course it's not nearly as good of a mimic as the other tangs....that was my question, could it be evolution in action? I mean, mimic tangs didn't develop their perfect mimicry overnight, it took many, many generations of ones that looked just a bit more like the angel than the previous one.

I completely agree with you that close inspection reveals how different they are--to a human eye. Of course, our keen eyes can also easily spot the difference between the true mimic tangs and their angel counterparts. A passing predatory fish might not have the same intent gaze, or even the keen eyesight we have, to distinguish between the two.

I wasn't aware that Chevron tangs ranged outside of Hawaii, I *thought* I read that they were endemics. This certainly puts a hole in the idea, I guess.

Thanks for your comments and the link,
Matt