Mebbid
Aquarium Advice Addict
I read through both of those and there is absolutely nothing supporting it. Just 2 random individuals suggesting it in a forum just like this. This above quote is in its entire context and is an opinion not any sort of factual statement with evidence.
I don't mean this in a bad way, thanks for looking them up. There just isn't anything in those to support the theory either, just a few people inferring it. It would be neat to test. If done do it properly with the whole scientific method and we can put it up to a peer review here on aa, try to replicate it. I'm in, lol, but I digress. Getting off topic.
The only way we could give this a true scientific test is to have it done with no less than a dozen tanks with guppies all from the same clutch preferrably from a true breeding strain. Other than that there's too much genetic variability to determine whether or not the temperature truly makes a difference. I don't know many people that would be willing to do that.