A team of scientists at the Imperial College London tackled the problem and published their results in Nature magazine (March 25, 2005). They decided to use yeasts, which are single-celled fungi, because they can reproduce both sexually and asexually, are easy to keep in the lab, and reproduce very rapidly.
Yeasts normally reproduce asexually, but when they are stressed (starved, high temperatures, etc.) they will reproduce sexually. The scientists did not want this switching to occur. So they genetically manipulated one asexual strain. They deleted the two genes (SPO11 and SPO13) required for normal meiosis, so that sexual reproduction was impossible. Now they had two pure strains—asexual and sexual.
The Imperial College team decided to compare the reproductive rate of the asexual vs. the sexual yeasts in two different environments: harsh and benign. That is, “fitness” would be measured by comparing the growth rate relative to the non-evolved ancestral strain. The benign environment had plenty of nutrients although glucose was limited so that growth was not uncontrolled. The harsh environment had the same glucose concentration but was at a higher temperature and had more demanding osmotic conditions.
Originally published at http://www.sciencecases.org/birds_and_bees/birds_and_bees4.asp
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