Experimental evolution in Chlamydomonas .1. Short-term selection in uniform and diverse environments

Genetically diverse cultures of the unicellular chlorophyte Chlamydomonas were selected for about 50 generations in a heterogeneous environment, comprising eight different culture media, and in a uniform environment consisting of the average of the eight different media. The genetic variance of fitness, either across or within media, was reduced much more severely in the uniform than in the heterogeneous environment. This effect appears to have been caused by the obstruction of directional selection in the heterogeneous environment, leading to the retention of a greater quantity of genetic variance in the short term.