[jamesfisher]

Can a decrease in oxygen from 35% down to 21% really explain a decrease in insect size from eight-and-a-half feet down to just 3 inches? Is there an interesting mathematical relationship here, or are there more factors at work?

[aatish]

Great question!

We spoke to Jon Harrison about this (the scientist we interviewed who studies insect growth & respiration). He says that the truth of the matter is we don't know the answer, it's still a hypothesis that the way insects breathe keep them small. There are other competing explanations, like that it's insect's exoskeletons that constrain their size, or ecological arguments (fewer predators means they can grow bigger). Also spiders don't use trachea to breathe but are also small.

One piece of evidence favoring the oxygen hypothesis is research that shows that the fossil record on giant insect size correlates with the oxygen levels in the past, all the way up until birds evolved (and wiped out the ecological niche for giant flying insects!)

http://blogs.discovermagazine.com/notrocketscience/2012/06/0...

And I'm told there's some more interesting work along these lines that's yet to be published.. so hopefully we should know more soon.

Lastly, there's all kinds of experimental work on breeding insects in high oxygen environments, but the results so far aren't universal.. some kinds of insects grow bigger, other's don't. The idea being that oxygen can help the insect grow but can also do damage to cells (in a way similar to aging), so you may need a long while to evolve and adapt to higher oxygen levels.

[CaptSpify]

> Lastly, there's all kinds of experimental work on breeding insects in high oxygen environments, but the results so far aren't universal..

In my completely uneducated experience, it seems like this should be easy to test. Wouldn't it be easy/cheap to over-oxygenate a room, and put bug-farms in there. Is it more complex than that?

[aatish]

The issue, I think, is that experiments like that would only tell you so much, because the insects aren't adapted to the high levels of oxygen (which can be kinda toxic, particularly at higher concentrations). So to really understand this you'd need to breed insects in high oxygen over many, many generations, and have them evolve in this new environment. That takes a lot of time and money. Jon's lab has done it with fruit flies, and they do grow bigger over the generations. But as far as I know (which isn't a lot), folks haven't done those kinds of multi-generation experiments in many species.