One hundred generations of artificially selected algae

Artificial selection is a form of experimental evolution used in research to enable scientists to study populations across multiple generations and ‘select’ for specific traits or phenotypes.

This type of research requires organisms that have short generation times and are easily cultured in the laboratory. At the Centre for Geometric Biology, Martino Malerba and Lucy Chapman have been experimentally evolving the green microalga Dunaliella tertiolecta in the specially designed algal lab at the Jock Marshall Reserve at the Clayton campus of Monash University.

They have been selecting for size and creating both big and small algal cell cultures as well as the intermediate sized control cultures.  To do this they need to select for the largest and smallest algal cells at each generation time to result in an evolutionary shift in body size.

Due to the robust cell walls of algae, centrifuging can be used to select for size in algal cells. Cultures are centrifuged twice a week and the supernatant (consisting of lighter, smaller cells) is removed to select for small body size and the pellet (heavier, bigger cells) is used to select for the larger body size.  Control cultures are also centrifuged but are shaken to re-mix all cell sizes before removing a sample for ongoing culture.

Recently Martino and Lucy reached the 100-generation milestone in the experimental evolution process. They have successfully evolved big and small algal cells with the control cells remaining intermediate in size.  Even after 100 generations the bigger cells are still getting bigger, although the smaller cells have stopped getting smaller.

The experimental evolution of different cell sizes allows Martino to investigate the consequences of size evolution on the physiology and ecology of this species through the measurement of a range of anatomical, physiological and ecological traits.

If you would like more information about this research, contact Martino.