I raised tadpoles of the Common Frog (Rana temporaria) from populations in eight source ponds in southern Sweden, in a common garden experiment at two densities. Tadpoles from different populations differed in development rate; those from source ponds with high tadpole densities developed faster than those from less crowded ponds. Thus, differences among ponds in tadpole performance, which were documented in previous field studies, must have a genetic or maternal component. This result of source pond crowding likely resulted from microevolution and is an example of countergradient selection. In contrast, I found no significant effect of source pond hydroperiod; tadpoles from temporary ponds grew and developed at a rate similar to those from permanent ponds. Tadpoles of R. temporaria can respond plastically to pond drying by increasing development rate. I suggest adaptive plasticity in development rate decreased selection by pond drying in natural ponds.