Dragonfly evolution question

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Bridge

Registered Senior Member
I'm trying to work through this problem of visualizing something happen. Part of the problem is the huge amount of time that has passed. I understand that dragonflies are ancient insects. Some fossil specimens have been found and dated at around some 320 million years old. Evidently the modern dragonfly and its ancestor don't differ much except in size. One group called Protodonata had a wing span of up to 75 cm.

Is it possible to manipulate a dragonfly in the laboratory and increase its size today? The other thing I'm puzzled by is I'm trying to determine the advantages and disadvantages of size. Presumably a very large dragonfly would be less prone to predation by smaller spiders, fish, etc. An obvious advantage to being smaller is you're less likely to be spotted by a predator but again now you're fair game for smaller predators on the same level. Are there any known studies on what environmental pressures caused dragonflies to get smaller? Just curious.
 
There was a theory for a while that Earth's atmosphere used to be a higher density, which would allow heavier/larger insects to fly.

This theory was intended to explain the flying abilities of pterodactyls (although more recent thought might suggest that they had feathers, along with the rest of the dinosaurs, which might change things).

It is probably possible to grow much larger versions of various animals under lab conditions - there was a researcher in Scotland (AF Protein, I think) that was growing fish like Atlantic Salmon to huge sizes.

However, a flying creature like a dragonfly probably won't fly if it gets too large. Also, there are limits to the insect circulatory system (an open system, unlike ours) which will probably keep the insect relatively small, at least compared to the Protodonata. There's no guarantee that the old dragonflies were physiologically comparable to modern dragonflies.
 
There's no guarantee that the old dragonflies were physiologically comparable to modern dragonflies.
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Excellent point and one I have never considered. Of course, then again one always gets more questions than answers when probing into these types of queries. Thanks for the reply Blue.
 
If you gave the insect a heart of some sort (possible if your going to be tinkering with them genetically) I would say they could get a bit bigger than a welsh corgie. After that their exoskeletons would have to be too bulky to support it. (unless you found something beter than chitin to use for it)

As for flying animals I doubt they could get much more massive than a ravin. Gossamer wings couldn't handle it. (again thats unless you can find something stronger that they could grow into wings)
 
Clockwood:

Insects already have hearts. The problem with the insect circulatory/respiratory system is twofold.

1) The surface area/volume ratio for a dragonfly is much larger than ours (it has a greater surface area for its volume, that is). The amount of oxygen that it could respire into its blood would decrease as its size increased - eventually it would be sluggish and unable to fly.

2) Insects like the dragonfly have an open circulatory system. That is, instead of having blood vessels the way we do, their entire body cavity (between their organs) is filled with blood, and the blood is moved constantly through the entire body, being oxygenated at the exterior membranes and absorbing food directly from the digestive system. This system works perfectly well for tiny insects, but for great big things like us it's not such a good solution.

Why? Well, gravity naturally pulls all of our blood down to the ground - that's why all of our blood vessels have valves in them so they don't backwater. When a pilot does a high-g turn in a jet plane, all of these valves relax and the blood sloshes down into their legs. That's why they black out - no blood in the brain.

So, the open circulatory system doesn't work well for large things like us because there's no reasonable way to move the blood to the top.

As for the exoskeleton comment, I think you're entirely right. A giant insect wouldn't have any internal skeleton, and so its organs (once they got too heavy) would press on one another.
This is probably why all the really big arthropods live underwater, where buoyancy keeps them from crushing themselves. (Ditto underwater mammals like whales.)
 
Some sort of lung then? You could design one just by changing the shape of existing tissues without creating new ones. As for supporting the organs and reinforcing the exoskeleton I suppose you could have internal "struts". It would be sort of a compramise between endoskeleton and exoskeleton.
 
I'm not sure if this is acceptable reply, but...

Clockwood,
were you implying that large insects can be made by somewhat 'fusing' insects and chordata?
 
The level of oxygen may have been higher in the Carboniferous, allowing giant arthropods such as Meganeura, Megarachne and Arthropleura; this would allow the larger body size while keeping spiracles, simple openings into the body cavity, as the method of oxygenation.

Apparently the evidence for a thicker atmosphere is less conclusive, but I suppose itis possible; the world was a very different planet then.
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Hey, as far as genetic modification of insects and hybridisation with mammals go, this may well come about in a few hundred years or so. Several genes are similar between chordates and arthropods (like eyeless IIRC) and perhaps a creature will be possible with features of both.

It will perhaps be easier to hybridise echinoderms and chordates, as they have more features in common (or so they used to say years ago), but who knows.
Not me, obviously; but neither does anyone else yet.
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To increase the size of dragonflies, you're probably better off breeding for size than trying to modify genetically - it's much cheaper. (I don't know how easy it is to breed dragonflies in captivity, but it's probably easier than the >$100,000 you need for a gene lab.)

You could test eburacum45's theory about greater oxygen content a little more easily though - see how a higher oxygen atmosphere affects large dragonflies.

The biggest dragonflies I've seen had a wingspan of 18cm or so.
 
I think temperature has alot to do with thier decreased size. This is only an anecdotal theory however. Where I live, large dragonflies only come around in the peak of summer and small ones are always around. And somewhere like florida where it is warmer, has alot more large dragonflies. It was alot warmer before the age of mammals, and this probably made it easier to be large.
 
Originally posted by curioucity
were you implying that large insects can be made by somewhat 'fusing' insects and chordata?
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Not really fusing... just having one borrow ideas off the others. I guess you could genetically "cut and paste" lungs and a circulatory system from a vertibrate to an insect. The internal struts as far as I know do not currently exist in nature.

It would be possible. A piece of dna in a lightning-bug does the same thing if put into a lab-rat. (if in a slightly different way) You can even get yeast to grow spider silk and they are definatly not close relatives.


Originally posted by BigBlueHead
To increase the size of dragonflies, you're probably better off breeding for size than trying to modify genetically - it's much cheaper.
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But it would take you hundreds of years of intensive breeding to increase their size even a little. Not to mention you would need to breed mosquitoes to feed them and you would need to find them a source of blood.
 
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Originally posted by Clockwood
Not really fusing... just having one borrow ideas off the others. I guess you could genetically "cut and paste" lungs and a circulatory system from a vertibrate to an insect. The internal struts as far as I know do not currently exist in nature.

It would be possible. A piece of dna in a lightning-bug does the same thing if put into a lab-rat. (if in a slightly different way) You can even get yeast to grow spider silk and they are definatly not close relatives.
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those are all examples of the expression of a single foreign protein which is relatively simple. To grow a complex organ completely different in structure would be a daunting task. And insects do have lungs of course. They are just called differently.
 
When Dragonflies were larger, there were no birds or bats to compete for food. I think that the evolutionary niche that large Dragonflies would fill is occupied now by insect eating birds, and to a lesser degree, bats.

I think it is similar to why Carcharodon Megalodon is now extinct. Scientists speculate that the cooling of the ocean caused the exstinction of these monsters. But its smaller relatives are still with us today.
 
Clockwood (not Chaosin - sorry) said:

But it would take you hundreds of years of intensive breeding to increase their size even a little.
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It only took hundreds of years of not-so-intensive breeding to make a wolf into a chihuahua. Most animals have a wide range of characteristics within the species, and it would not be a big chore to collect only the large ones and breed them together to see what the already extant upper limit was.

As for the food criticism, I don't know enough about dragonflies to say, but I would assume that they could be fed farmed insects without too much trouble.

If you wanted to engage in an experiment, you could try to get it taken up as a conservation effort for one of the endangered ones.

*edited for misreference
 
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