Testing the fitness of biologi...( nd group. The researchers were careful ...)

They then mixed the algae with disrupted clocks with algae with normally functioning clocks. When the mixture was placed in an environment with a 24-hour day/night cycle, the normal algae grew dramatically faster than those that lacked functional internal timers. The normal algae also outperformed the algae with the damped clocks, but by a smaller margin.

The result was presaged by a series of experiments that Johnson conducted in 1998 with Susan S. Golden from Texas A&M University and Takao Kondo from Nagoya University. In the previous experiments, the researchers created two new algae strains with clocks of 22 hours and 30 hours. (The frequency of the biological clocks in normal blue-green algae is 25 hours.) They created mixed colonies by combining the strains in pairs: wild type and 22 hour; wild type and 30 hour; 22 hour and 30 hour. Then they put these mixed cultures into incubators with three different light-dark cycles--22 hours, 24 hours and 30 hours--and monitored them for about a month.

When they pulled the cultures out, the researchers found that the strain whose internal clock most closely matched the light-dark cycle invariably outgrew the competing strain. In fact, they found that the selective advantage of having the correctly tuned biological clock was surprisingly strong: The strains with matching frequencies grew 20 to 30 percent faster than the out-of-synch strains.

The second part of the current experiment was designed to test whether the biological clocks also provide an intrinsic advantage, a hypothesis advanced by the late Colin Pittendrigh of Stanford. He suggested that circadian clocks might be beneficial even in an unchanging environment. There was some indirect support for this proposition. In one experiment, for example, populations of the fruit fly, Drosophila melan
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Contact: David F. Salisbury
david.salisbury@vanderbilt.edu
615-343-6803
Vanderbilt University
23-Aug-2004