[Odonata-l] Oxygen and insect gigantism

[Nick and Ailsa Donnelly]

This is getting philosophical.  I believe excess Permian oxygen is not the
answer, as I have said.  A scale-up of 4X requires a lot of thought.  Let's
try a thought problem.  Suppose that the largest birstd extant were
sparrows, and that we investigated the phisiological scanilg in the range of
hummingbirds to sparrows.  Then someone finds a fossil condor.  How can that
be? Everyone asks.  If we look at sparrow phisiology then we see that we
can't scale this up to condor size.  But somehow exactly this did happen.  '

I suppose that if the larger members of a group become extinct for whatever
reason (I suggest predation for dragonflies, plus the evident physiological
demands for eating and growth of the laregr forms), then it should follow
that the successful, relatively diminutive descdants will not necessarily
retain sufficient physiological potential to be "re-scaled" to the previous
large size.

When you have a range of observations, it is never satisfactory to scale
beyond your observable limits.

Nick Donnelly

-----Original Message-----
From: odonata-l-bounces at listhost.ups.edu
[mailto:odonata-l-bounces at listhost.ups.edu] On Behalf Of Roy J. Beckemeyer
Sent: Monday, July 14, 2008 8:28 PM
To: odonata-l at listhost.ups.edu
Subject: Re: [Odonata-l] Oxygen and insect gigantism

An interesting paper on this subject was published last year in PNAS.  It is
available in pdf form at: 
http://www.pnas.org/content/104/32/13198.full.pdf+html
Kaiser et al found evidence supporting oxygen limitation as a factor in
insect gigantism because of increases of tracheal investment with size
observed in extant beetles.  Cross-sectional area of the tracheae in the
legs increased with mass to the 1.07 power while cross sectional area of the
leg varied with mass to the 0.77 power - i.e. tracheal area would become
limited by size limits of the leg structure as the beetles got bigger.
Anyway, I believe folks who have commented on this thread thus far might
like to read the paper.  PNAS papers are pretty much all available for free
at their web site.


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