The Difference in Temperature Preference Between Two Populations of Daphnia $\degree$

The difference in temperature preference between two populations of Daphnia water fleas is due to a mutation. The original population prefers temperatures near 20 $\degree$ C, while the mutant population prefers temperatures between 25 $\degree$ C and 30 $\degree$ C. Predict how natural selection might affect the geographical distribution of these two populations.