@DocZ
Thanks for bringing this up!
I think it's a really important and valid question that should be thought more carefully about. I don't know the answer, but I can't find any studies or documentation demonstrating how that temperature was obtained. Frankly I think it's not backed by much although maybe I just didn't come across the full documentation that exists.
One thing that might be of interest-obviously your points above about basic principles of vertebrate airway activity are correct, but there are some studies indicating a higher risk of pneumonia or COPD admissions in elderly humans when it is hot and humid out.
https://pubmed.ncbi.nlm.nih.gov/29730816/
And here but I didn't have time to find the publication they reference
https://www.lung.org/blog/weather-and-your-lungs
There's a lot of other literature demonstrating that warm and humid air can provoke other issues with ones' respiratory system. I found this interesting. It suggests to me that warm air combined with humidity might actually be damaging to humans, who obviously are far different than chameleons as far as lung structure and physiology. Possibly, we are less sensitive and more resilient just because for many of us, our basic needs are known and met more effectively than are for chameleons in captivity so we have more buffer to respond to infection etc. than they might. Total speculation there. However, seeing these data, I think there is precedent that some of this applies to chameleons as well. I won't get into every critique of every study above because I'm not trying to write a review paper, but it might be of value in this discussion.
Perhaps the deleterious role of humid, warm air on respiratory health has to do with modulation of inflammation, disrupting osmotic balance, vasodilation, you name it, but I suspect that the idea that bacteria grow in the air unless temperatures are arbitrarily somewhat low (67-68) is incorrect and basically misinterpreting what is actually going on. A million types of bacteria grow at much colder temperatures. It's simply wrong to say that bacterial growth is stopped at 67 degrees. What I bet is happening is fogging during warm temps causes some kind of damage or stress directly to the chameleons' respiratory physiology, and this renders them susceptible to bacteria that are already present.
I think this is further supported by some experiences I have had, wherein the difference between infection and hydration was a matter of overwhelming (my interpretation) chameleons with too thick of fog. When raising baby trioceros ellioti and hoehnelii I had some issues with RIs for babies when tweaking a fogging system. Dispersing very dense fog over a shorter period (despite providing airflow), while increasing the nighttime humidity to a similar degree as lighter fog dispersed over a longer period, would cause RIs, and the lighter fog would not. I think what happened was the dense fog basically overwhelmed the physiological capabilities of their lungs or otherwise respiratory tract, whereas the lighter fog didn't, despite the overall humidity being similar. Kind of like how one could lift 100 pounds 10 times, but one couldn't lift 1000 pounds once. That's my interpretation anyway.
Different species have different tolerance for fog inhalation it seems. I have had c. linotum next to f. lateralis in completely identical setups on the same fogger setup, where with everything identical (and fogging at 57 degrees or 60) the c. linotum absolutely thrived and the f. lateralis developed RIs within a couple of days. I suspect this is because c. linotum is adapted to inhaling that high level of fog, and as such, has physiological adaptations that prevent whatever damage is occurring, whereas f. lateralis does not (in this scenario, based on what I provided). Just an example, there are others.
To me, what we observe in captivity is much more in line with what I describe above (physiological response to overly humid air or too warm of humid air delivered in the wrong way) than this idea that bacteria only grow at an arbitrary (and debunked in the medical literature, look up any staph aureus, pseudomonas etc. growth rates) temperature. So in short, I think 67 degrees is probably based on some solid observations, as it tends to hold generally true that fogging is safer at temps there and below, but I think this reason for this is different than commonly described. Understanding whether temps of 68 or higher impact chameleon vasodilation/constriction or epithelial cell integrity in lungs, or other avenues of investigation like that would probably give us more insight into the answer, in my opinion.
That went on longer than I expected. This is just speculation on my part. I hope someone finds some value in this impromptu essay haha. I'd be very interested in everyone's opinions on this, and thanks for bringing this important topic up for discussion!
