Note that I am NOT asking "which organism can survive the most extreme temperatures." Many extremophiles like the tardigrade can survives extreme heat, but also extreme cold. Many heat adapted animals like the camel can also tolerate fairly cold conditions. I want to know what species that are adapted to hot climes are hot climate obligates (or the corollary for cold climate obligates) and which extreme temps-obligates have the narrowest tolerance.

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    $\begingroup$ the icefish must have a pretty narrow band of temp tolerance since they have no hemaglobin and the really cold antarctic water is loaded with O2 $\endgroup$
    – dblyons
    Commented Jan 31, 2017 at 1:49
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    $\begingroup$ I don't have a precise answer for this, but if you want to do some more research on your own to try to find answers, I have two guesses for directions to take: 1) Parasites of warm-blooded hosts. I would expect these to have some mechanism for survival between hosts, like a spore or egg phase, but they would do all their growth, reproduction, etc, inside a nice, comfy host and they would have enzymes adapted for the host condition. 2) Extremophiles, like you mention, that are so adapted for strange conditions such as ocean vents that they cannot survive outside these areas. $\endgroup$
    – Bryan Krause
    Commented Jan 31, 2017 at 2:51
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    $\begingroup$ (also, if you are wondering about animals you really need to specify animals; otherwise, unless you are talking about sizes of individuals or something like that, "what is the most" or "what is the least" questions have a high probability of leading to bacteria/archaea, or if you need a eukaryote then protists) $\endgroup$
    – Bryan Krause
    Commented Jan 31, 2017 at 2:54
  • $\begingroup$ @BryanKrause obligate-symbionts is a really good thought since their host takes care of providing a homeostatic environment. Thanks for that thought! I thought about ocean vents, but in reality, those environments fluctuates quite a bit since the temp varies wildly at the boundary layer between deep-ocean cold water and magma-hot water. Also, just to note, I'm not specifically asking about animals, but I suspect sedentary organisms probably adapt for greater fluxes since they cannot cope with temp changes through vagility. $\endgroup$
    – et is
    Commented Feb 1, 2017 at 14:10


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