The environment of an organism determines the selection pressures on it. For example, organisms with the ability to camouflage in a forest environment are more likely to survive, and be selected to pass their traits on.
The answer to that would be archaebacteria since they are prokaryotes (no nucleus) but so is Eubacteria, however archaebacteria can live in very harsh conditions.
Blood vessels expand during hot weather and retract/ tighten in cold weather
