Adaptation of Paramecium caudatum to variable conditions of temperature stress.

The environment is rarely constant and organisms are exposed to spatial and temporal variation that will impact life-histories. It is important to understand how such variation affects the adaptation of organisms to their local environment. We compare the adaptation of populations of the ciliate Paramecium caudatum exposed to constant (23 °C or 35 °C) and temporally variable temperature environments (random daily fluctuations between 23 °C or 35 °C). Consistent with theory, our experiment shows the evolution of specialists when evolution proceeds in constant environments and generalists when the environment is temporally variable. In addition, we demonstrate costs for specialists of being locally adapted through reduced fitness in novel environments. Conversely, we do not find any costs for generalists, as all populations from variable environments had equal or superior performance to specialists in their own environment. The lack of a cost for generalists is emphasised by the presence of a super generalist that has the highest performance at both assay temperatures.