EXPERIMENTAL EVOLUTION IN CHLAMYDOMONAS .3. EVOLUTION OF SPECIALIST AND GENERALIST TYPES IN ENVIRONMENTS THAT VARY IN-SPACE AND TIME

Lines of Chlamydomonas were selected for growth either in Light or in Dark conditions for several hundred generations. Evolved lines that gr ew well in the environment of selection grew less well in the other en vironment, so that negative genetic correlation between Light and Dark growth was created by selection. The existence of a cost of adaptatio n was confirmed by reverse selection. The lines were also exposed to e nvironments that varied either in space or in time with respect to Lig ht and Dark conditions. Specialization (genetic variation) was retaine d in spatially variable environments, whereas generalization (phenotyp ic plasticity) evolved in temporally varying environments. The origina l negative correlation between adaptation to Light and Dark conditions seemed to be caused primarily by mutation accumulation rather than by antagonistic pleiotropy. It was thereby possible to select a generali st type nearly as well adapted in each environment as a specialist lin e.