Just tested this while waiting for the login queue:
Leveling a Mightyena from level 18 to 19 is 1,021 exp with it's current exp at 5,838.
Leveling a Poochyena from 18 to 19 takes 1,007 exp with it's current exp being at 5,852.
Note the difference in the two battles I just tested was 14 experience lower on the evolved form from the unevolved form.
So the exp needed to reach 18 to 19 on either evolved or unevolved Poochyena from 18 to 19 means it has to have a total exp of 6,859, and I'm the OT of the Poocheyna, so it doesn't get any bonus exp.
This means on the handhelds, evolved and unevolved Pokémon have no different in leveling required.
So, given that this is the case if the admin or someone that speaks for him could answer: Did you choose to make it take more experience to level up an evolved Pokémon? If so, may we know why? I'm asking, because I'm a new player, and I was totally unaware of this when I evolved my starter, and I'm disappointed now that I will have to grind out a lot more battles to level my Pokémon than if I hadn't evolved it...