Over a short period of time, adaptation would not be effective because of the time limit. Homoestatic Function would fail to balance the heat and as such, too much loss of water would eventually kill the rat.
But for a long period of time and most likely progressively, there would be adaptive response from the rat
I found plenty on why there are different. if you would like a sarcastic answer I would suggest "they both keep swimming, swimming, what do we do we keep swimming swimming. "
