I’m curious as to how biologists unpack the presence of these kinds of adaptations:
(Choeradodis rhomboidea, from a post on BioLogos. I don’t know the original image source.)
First, when one looks at this design, it is quite easy to say that it is intentional. So, would an evolutionary biologist observe this and say that it is merely beneficial and fortunate that the coloration so closely matches that of the leaf (including the white, scaly splotches)? Would it be presumed that these were from “random mutations” that developed slowly over time? Obviously, one would not expect the insect to observe its environs and to guide or direct the evolution of this species.
I’m just wondering about these and other visual adaptations and the thoughts that are evoked when one sees something that seems to be so intentionally matched (camouflage to the environment) like this.
What do you think needs unpacking? Insects with a coloring closer to the leaf’s green color had slightly better camouflage and a slightly better change of surviving to reproduce. The same with those more leaf-shaped than those without. After millions of generations of natural selection pressures you get insects with a remarkable ability to mimic the plants they live on.
It’s not simply decent camouflage or just color, it’s really quite detailed. I have a hard time reconciling the slow speed of evolution with the specificity. In some ways it would be easier to understand a generalized chameleon-like ability to adapt color to environment, but this is much more specific. And how on Earth do you get those physical features from DNA?
Each generation you get random genetic changes producing small morphological changes. Some of those physical changes looked slightly more like leaves than others and provided a small survival advantage. The insects with those genes reproduced slightly more that others so the genes for leaf similarity spread through the population. Wash, rinse, repeat over millions of generations and eventually you get amazing similarity.
These kinds of adaptations are the very things natural selection explains.
Mantises are often exquisitely camouflaged, not only to escape predators but also to be able to jump on their unsuspecting prey. Their camouflage is used both defensively and offensively. They’re under a sort of double selective pressure, both from their natural enemies who eat them, and from the prey they stalk.
I think that’s the crucial question here. If we can understand the genetic causes of their camouflage, we can probably also understand how they’ve been able to evolve to so perfectly mimic their many niches.
I think this is perhaps the part that people maybe have a hard time with, I know I do. It’s probably just some of my not being a biologist, but when I think about a few-to-tens of thousand genes in a genome, each one resulting in a protein/enzyme, it’s hard for me to think that that’s enough “knobs” to turn to make these small morphological changes. Aren’t genes mostly producing something more “critical”?
Virtually all physical features in your body are produced from genes, from the most critical heart valve to the most unimportant shape of your earlobes. Small physical changes to features, especially the non-critical ones, happen every generation. If the changes provided a survival advantage they get selected for and tend to accumulate. It really is just natural selection acting on random variations.
The actual green color might require modification of an existing protein, or conceivably even a new protein, but where it is displayed and surface patterns are likely to be changes to gene regulation, not to genes themselves, and not terribly complex ones.
Try something harder: how can turning on and off a bunch of proteins code for a brain with an instinctive ability to detect and fear snakes, say? We have no idea how to design something like that. Which is why Intelligent Design has it backwards: lots of biological features are built in ways that evolution can accomplish but that intelligent design can’t, at least not any intelligent design process we’re familiar with.
Mantises (and grasshoppers and other arthopods) molt several times during their life cycle. In temperate zones, where vegetation changes colors in the fall, many molting insects have green skins in the spring and summer, but get more yellow and brown skins as autunm arrives.
Tropical mantises show little color changes over their lives.
On a related note I wonder if you have ever read Richard Dawkins’ The Blind Watchmaker? Whatever any of you may think of Dawkins public atheism and views on religion, he really is a very good popular science writer and has a gift for metaphor and explaining natural selection.
Right, so gene regulation is what I was thinking might be the key, although frankly I don’t know much of anything about it. My biology classes were either focused on DNA and genes themselves or things like conservation biology, but I didn’t get much about the middle (basically cell biology). As physical chemists go I think I do OK, but there are times when I’m keenly aware that I’m not a biologist.
Natural selection is conceptually easy for me, it’s stuff like this and what @glipsnort said that seem incredible.
As someone who helped design artificial molecular motors as a graduate student, this is how I feel about biological motors. They are way more complicated than “intelligently designed” motors and very different from anything we would design.
Wow! That’s amazing. It really blows my mind that this stuff is encoded in DNA.
@Jordan, As far as “the slow speed of evolution” goes, maybe it isn’t as slow as you think. Creationists like to declare that one must wait millions of years for one gene substitution, before you can get another. Except in special cases, these arguments are wrong. Animal and plant breeders know better – they can make progress in multiple traits at once (especially when there is already genetic variation in the population).
Also, changes in gene regulation need not be dramatic and cataclysmic. Substitutions of modest effect in gene regulation will be quite common, though we tend not to find it easy to study them if their effects are small.
Batesian mimicry (which is what this is) has been studied extensively since Darwin’s day. There is lots of literature on it, which you should take a look at.
I’m with you on this. For years I was in a twilight zone where evolution seemed to me to make sense from a fossil history point of view, but the mechanism did not feel adequate. As I came to appreciate more that the greater part of what distinguishes one animal from another is not so much that its proteins being different as their expression is being modified, the picture became clearer for me.
This is something I wish was more communicated to the general public. A mutation in an actual protein coding segment of DNA might be occasionally beneficial, but most people are familiar with several horrible, tragic diseases which are due to coding mutation. So when they hear that all the wonder of life is due to mutation, they are reasonably suspect of that claim. But much of the distinctive attributes by which we recognize some given animal is visibly a matter of degrees of expression. More green, more brown, more mottled or striped or speckled, bigger, smaller, more hairy, pointy teeth, flat teeth, narrow soaring wings, flapping wings, limbs, flippers, all do not generally depend so much on having different proteins as being expressed in different intensities and arrangements. Now of course closer inspection may reveal differences in many related proteins, but the point is that nature molds a menagerie of creatures out of similar materials of keratin, cartilage, and what constitutes our bone, flesh and blood. It is easy to envision that a change in expression is less likely to be traumatic to an organism, being a matter of degree, than a change in protein.
I do not think this really comes across in the PBS, BBC, and like documentaries which touch on genetic variation, which leave the lay audience with the impression that most of mutation concerns coding for proteins, at least IMHO. This may result in a something of a public misunderstanding of the machinery of mutation.
Thanks Tim. So, when you say “mimic” you are not speaking of mimicry, as in the octopus taking on the coloration of its surroundings in real time. I agree that this looks like “mimicry” but it certainly cannot be, at least in the same way. Rather, it would have to be unintentional and fortuitous mutations that occurred, but only seem to look just like a torn leaf with scale, right?
Thanks, Steve. So, then, you also would see the patterns not as intentionally mimicking the damaged, leaf, but rather that it is merely a series of fortuitous mutations, driven by selection?
This is very cool!
How modest an effect in gene regulation would we be talking about here? Maybe one can’t even answer that question. But, clearly, we’re not speaking about black vs. white moths, but rather a green insect with an “image” of sorts that seems to depict a tear in a leaf, along with some oxidation along the tear, and some scaly spots as well. What would need to be modified so that this kind of pattern that seems to be a depiction of a leaf to occur?
Would one imagine that the insect was once green, but then these patterns occurred as adaptations over time? I’m guessing that no evolutionary biologist is going to perceive these patterns as intentional representations of (in this case) a torn leaf, right?
Turns out the spots (at least the grey and white ones) are actually different species of liverworts, lichens and fungi growing on the mantis. Apparently these are common on insects that mimic leaves. The parasites grow on the leaves and eventually spread to the insect too, incidentally improving the camouflage effect.
Here’s another one, but where the pattern is symmetrical, indicating that it’s likely developmental, at least in this species:
How modest an effect in gene regulation would we be talking about here? Maybe one can’t even answer that question. But, clearly, we’re not speaking about black vs. white moths, but rather a green insect with an “image” of sorts that seems to depict a tear in a leaf, along with some oxidation along the tear, and some scaly spots as well. What would need to be modified so that this kind of pattern that seems to be a depiction of a leaf to occur?
We’re not talking about going all the way to complete mimicry in one jump. Just getting a bit greener, or a bit more leaf-shaped. Each such change leads to a small increase in the percentage of predators mistaking the mantis for a leaf, or prey of the mantis making the same mistake. Small changes in regulation can do things like that. And the process continues until you get this amazing mimicry.
Would one imagine that the insect was once green, but then these patterns occurred as adaptations over time? I’m guessing that no evolutionary biologist is going to perceive these patterns as intentional representations of (in this case) a torn leaf, right?
No, the insect need not have started out green. It could have gotten greener and greener, each such change giving a bigger fitness advantage. Intention has nothing to do with it, as you will find if you read biology texts.
I am surprised that you don’t realize that the organism needs no “intention” to have mimicry evolve. The mantises that are the best mimics are not aware of that, they just need to get a fitness advantage from their pattern.
Go Huskies!
Yes, go. Go away on lots of away games, and don’t play in the stadium here because it messes up the parking near my office on Saturdays.
I suspect that when a new niche has been opened or when prey species are knocked back, populations with individuals having slight (out of the ordinary) differences are more likely to persist. And because mutations occur constantly and simultaneously throughout populations, these odd individuals will, on occasion, reproduce together, passing on multiple advantages. These offspring are even more likely to survive, and thus reproduce.
Why are you surprised? I only asked if evolutionary biologists would see the pattern as an intentional leaf pattern, or if they would look at it as a fortuitous set of mutations guided by selection.
Friday this week, so you can park to your heart’s content on Saturday.
So, Rich, you don’t see a “leaf pattern” per se, either? You see random mutations that merely appear to be in a leaf pattern? Biologically speaking, do odd individuals who reproduce together have a higher likelihood of passing along both of their separate mutations? Or no?
Why are you surprised? I only asked if evolutionary biologists would see the pattern as an intentional leaf pattern, or if they would look at it as a fortuitous set of mutations guided by selection.
… guided by selection which has higher fitnesses for genotypes, the closer the resulting phenotype is to mimicry of a leaf. Note that the mutations need not be new ones, those alleles could be floating around in the population even before selection starts to work.
So is it “intentional” if fitnesses increase as mimicry increases? Or is it “fortuitous”? Neither. It is certainly very nonrandom if fitness is affected by mimicry.
