[Odonata-l] help with oxygen...

[Richard Rowe]

Ethan Bright wrote:
> Further to Nick's answer, recent work on insect respiration and 
> physiology (e.g., Westneat et al. 2003, Science 299(5606):558-560) 
> suggests insect respiration isn't so passive, so ambient oxygen 
> concentration changes during the Permian probably weren't a huge factor. 
> Further, the issue isn't just predation on adults; I'm sure that larger 
> odonates required longer periods for nymphs to develop. That would have 
> made them susceptible not only to fish and immature amphibian predation 
> (and probably other arthropod and invertebrate parasites), but also 
> probably to the increasingly drier continental conditions (and higher 
> salinity?; also higher dissolved oxygen stress?) of the later Permian 
> aquatic environments.
>
> Nick and Ailsa Donnelly wrote:
>   
>> I believe oxygen could not be the correct answer.  Numerous scaling 
>> observations relating body mass to oxygen consumption shows that the 
>> modest increase in oxygen that possibly existed during the Permian 
>> (when all the Caroniferous coal beds were buried and not yet exhumed) 
>> would have only increased size by a rather small amount - certainly 
>> not 4X linear dimensions (which is 64X body mass). 
>>
>>     
These references are a little older, but they are the work of the late 
Peter Miller, a very highly respected odonatologist.

Miller, P. L. 1960a. Respiration in the desert locust. I. The control of 
ventilation. J. Exp. Biol. 37:224-236.
Miller, P L. 1960b. Respiration in the desert locust. III. Ventilation 
and the spiracles during flight. J. Exp. Biol. 37:264-277.
Miller, P. L. 1960c. Respiration in the desert locust. II. The control 
of the spiracles. J. Exp. Biol. 37:237-263.
Miller, P. L. 1966. The regulation of breathing in insects. Adv. Insect 
Physiol. 3:279-344.
Miller, P.L. 1974. Respiration - aerial gas transport. In M. Rockstein 
(ed) Physiology of Insecta 2nd ed. 3: 557-615

In essence things like caterpillars can get by with diffusion (August 
Krogh's work in the early 20th century) but anything active uses dynamic 
methods for transporting oxygen to the tissues. There are many dynamic 
methods to which Westneat et al added one more ... The diffusion model 
which still persists in general textbooks is a libel on the vast 
majority of insects. Insect tracheal/air sac 'pumping' gets far more 
oxygen to tissues than mammals are capable of (or even for that matter 
birds),

Richard

-- 
Dr Richard Rowe
Zoology & Tropical Ecology
School of Marine & Tropical Biology
James Cook University
Townsville 4811
AUSTRALIA

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