by Greg Mayer
We’ve often highlighted here at WEIT the remarkable phenomena associated with mimicry, the often marvelously detailed resemblance of organic beings to other organic or inorganic features of their environment. On a trip to Costa Rica in January, while out for a nightwalk at La Selva Biological Station with Jon Losos, we came across a hooded mantis, probably in the genus Choeradodis, on a broad leaf. Many kinds of insects resemble leaves, having what Hugh Cott called a “special resemblance to particular objects”. The thorax is broad, flat, and the same color as the leaf, while the folded wings are leaf-shaped and have what looks like venation. The opened wings can also look leaf-like (browse the images here). There are even some mantises which mimic dead leaves. What struck me about this mantis, though, was that the insect also had a blemish on its thorax, looking very much like the blemishes on the leaves.
Can you tell which of the following is on the mantis, and which on the leaf? You probably can figure it out by using cues of lighting and haphazard details in this particular image, but not by any in principle distinctions.
What is remarkable about this is not just the resemblance, but the asymmetry of the blemish on the mantis, indicating that its position is unlikely to be a constant pattern feature. I do not know what causes the leaf blemishes– a fungus? insect damage? Could the blemish on the mantis also be an induced pattern element of some kind, but in this case one that enhances the mimetic resemblance, and breaks the symmetry of the insect?
I could not find any reference to asymmetric mimicry of blemishes in a quick perusal of classic references, or the internet. Are there any tropical biologists, entomologists, or plant pathologists out there who can perhaps enlighten us?
Cott, H.B. 1940. Adaptive Coloration in Animals. Methuen, London. [“reprinted with minor corrections 1957”]
Wickler, W. 1968. Mimicry in Plants and Animals. McGraw-Hill, New York.
Greg, I hope someone can come up with a reference, because I have seen the same sort of markings in the mountains of west-central Panama.
That its not symmetrical is amazing.
From looking at the pictures it seems many have the blemish on one of 2 asymmetical locations. The fact that its asymemetrical doesn’t surprise me too much (thats not hard to acheive developmentally). What I’m wondering is whether its different species or subspecies that either dont have the blemish or have it on different locations or whether the same population is variable in its expression.
I’d guess that the leaf spots are caused by a fungus, probably Cercospora, Pseudocercospora or related genera. These typically make circular “zoned” blemishes on leaves and fruits similar to those in the pix. These leaf-spot fungi are widespread and often econoically significant, attacking a very wide range of plants in both tropical and temperate climates.
I doubt very much that the mantid spots are disease — looks very much like a “specific resemblance” brought to us by our friends at Natural Selection Inc.
I noticed one had two spots asymmetrically locate on each end of the mantis. Another had a large wedge of black and yellow coming in from the outside edge. A most remarkable adaptation. You’d almost have to think they were caused by a fungus attacking the mantis. At least predators would be drawn to that conclusion.
Doing a Google Image search for the hooded mantis turns up more photos of such blemishes and other anomalies that make it look like a blemished leaf somewhat worse for wear. And they all seem random to me. This link has some excellent photos http://www.flickriver.com/photos/tags/hoodedmantis/interesting/. Then look at this one https://www.flickr.com/photos/andreaskay/6921845427, which sports a blemish that bears a remarkable resemblence to the tears in the leaf it’s on, as if it’s a leaf that had been damaged but healed. What’s going on?
What an arms race!
Asymmetry, and variable asymmetry has been noted elsewhere in leaf mimicking insects. There was a posting about this for a dead leaf mimicking mantis known as the ghost mantis, that I recall. Was it put up here in WEIT? I don’t remember, unfortunately.
As to how this might emerge, I have no idea. I can only hand-wavingly guess for transposons or something.
Yes, Jerry did a post on ghost mantises a while back https://whyevolutionistrue.wordpress.com/2016/01/10/readers-wildlife-photos-purloined-edition/ In them, it’s interesting that the within and among individual variability is morphological, not just in color. Thanks for remembering it– I didn’t!
GCM
The mimicry/etc posts here have been stimulating. It’s hard to express this – I mean I saw this years ago in high school, and thought “yep – mimicry, got it.”
But as soon as I started discussing the whole thing lately, I thought “holy ___ this is interesting! It’s challenging to really understand!”
Late to the party on this post, but I’ll take a stab at this challenge:
To my eye, the leaf blemishes show diffuse edges in the direction parallel to the leaf’s axis of vascularization, and sharp edges in the perpendicular direction. The faux blemish on the mantis seems more isotropic.