It’s great to know you’ll never hit your peak — fitness peak, that is. Bacteria in MSU BEACONite Richard Lenski’s Michigan State University lab are still growing ‘fitter’ even after 58,000 generations — and 25 years! — of living in the same, simple environment.
In a recent paper published in Science, Michael Wiser, lead author and MSU zoology graduate student in Lenski’s lab, compares this continual evolution to hiking. “When hiking, it’s easy to start climbing toward what seems to be a peak, only to discover that the real peak is far off in the distance,” Wiser said. “Now imagine you’ve been climbing for 25 years, and you’re still nowhere near the peak.”
Here, the peaks aren’t mountains, but ‘fitness peaks’, where the population has the optimum set of mutations so it can no longer improve, and any new mutations would knock the population down from the peak to a suboptimal state.
While biologists have known that organisms keep evolving as the environment changes, even when the environment is constant, Lenski asserts, “there doesn’t seem to be any end in sight…We used to think the bacteria’s fitness was leveling off, but now we see it’s slowing
down but not really leveling off.”
To determine the bacteria’s ascent toward possible fitness peaks, Wiser used hundreds of frozen samples—bacteria all the way back to generation 0 in Lenski’s 25-year experiment.
Because these bacteria were still alive, Wiser was able to compete samples of different generations against one another to measure their survival and ascent toward the potential fitness peaks.
From these samples, Wiser determined the bacteria’s ascent matched a mathematical function called a power law, which decreases in slope over time, yet never reaches a peak.
“It was surprising to me that a simple theory can describe the entirety of a long evolutionary trajectory that includes initially fast and furious adaptation that later slowed to a crawl,” co-author Noah Ribeck said. “It’s encouraging that despite all the complications inherent
to biological systems, they are governed by general principles that can be described quantitatively.”
This article understandably has received much attention, as it has been covered by National Geographic, New Scientist, National Public Radio, and even German radio stations have gotten in on the action.
So when will it all end? Not for many generations. This long term experiment continues to produce fruitful results shaping our fundamental understanding of evolution in action.
If this article has ‘piqued’ your interest, read more here: M. Wiser, N. Ribeck, R. Lenski (2013) “Long-term dynamics of adaptation in asexual populations,” Science [DOI: 10.1126/ science.1243357] Photo courtesy of MSU
[Written as part of my work with the BEACON Buzz]