From Jamil's website:
Q: Does a starter need to be kept at the same temperature as it is going to ferment the batch of beer later?
No, but there are practical limits to how high or low you can go.
Warmer starters (up to 98°F, 37°C) equal more rapid yeast growth, but using these very high propagation temperatures negatively affects the viability and stability of the resulting yeast. Very rapid growth or excessive growth can result in weaker cell membranes due to lower unsaturated fatty acid concentrations. Lager yeasts tend to be especially sensitive to high temperatures.
The cooler you ferment the starter (down to the planned fermentation temperature for the main batch) the slower the yeast growth, but the yeast can be healthier than yeast coming from a high temperature starter.
Keep starters between 65°F (18°C) and 75°F (24°C). A temperature around the low 70s (72°F, 22°C) strikes the best balance for the propagation of yeasts. Lager yeast starters can be kept a few degrees cooler and ale yeasts can be kept a few degrees warmer, but this temperature strikes a good balance of yeast health and efficient propagation for both types of yeast.
If you are going to pitch the starter at high krauesen, it is best to keep the starter within 5 degrees Fahrenheit (3°C) of the wort temperature of the main batch. Pitching a very warm, active starter into cold wort can stun the yeasts and with lager yeasts this can cause a higher incidence of petite mutants, which can negatively affect attenuation, flocculation, and increase hydrogen sulfide production.
You can add small amounts of cool wort to the starter over time, to bring the temperature down gradually, but it is really better to keep everything closer to fermentation temperatures from the beginning. Any time yeast sense a big drop in temperature, they slow down and drop out.