This week's paper is "Rapid evolution towards heavy metal resistance by mountain birch around two subarctic copper–nickel smelters", published in the Journal of Evolutionary BIology by J.K. Eranen.
Evolution is a change over generations, so evolution is typically faster (more change per year) in species with short generation times. Signficant evolutionary change in bacterial populations, therefore, can take only a day or two, under ideal conditions. Long-lived species like humans and trees evolve, too, but it takes much longer. So, for example, are trees likely to evolve fast enough to survive climate change?
Eranen studied birch trees that have been exposed to pollution from smelters in Russia. Near the smelter, these trees are typically much shorter (<2 m) than in less-polluted areas (>6 m). This difference is presumably due to some combination of the harmful effects of pollution, beneficial acclimation (nongenetic responses of individuals to conditions), and evolution (a change in the genetic composition of the population). An example of acclimation would be if, in polluted areas, shorter trees actually produce more seeds than tall ones.
To separate these effects, he did what is known, for historical reasons, as a "common garden" experiment, although the "garden" in this case was a greenhouse. Tree seeds from severely polluted areas near two smelters, and control seeds from less-polluted areas, were grown with and without addition of toxic heavy metals. With the toxic metals, trees from polluted areas grew taller, with bigger leaves. This is presumably good, although it would have been interesting to see data on seed production. Because seeds from both environments were grown under the same experimental conditions in the greenhouse, this represents a genetic difference, presumably due to evolutionary change over the 70 years or so that the smelters have been in operation. This could represent a few tree generations, depending on the age at which birches reproduce.
As is often the case, there was a cost to genetic stress resistance: in soil without toxic metals, the trees from less-polluted areas grew better. All of these differences were statistically significant -- that is, we can be 95% sure that they are not due to chance differences among trees -- but they were also fairly small. For example, in the pollution treatment, trees from unpolluted areas grew about 80% as tall as those from polluted areas. This may be because soil concentrations of nickel and copper in the experiments were about one-third what the trees had been exposed to in the polluted areas.
So evolution is detectable in trees, but will it be fast enough to allow trees to survive in their present locations? Or, as boreal forests warm, will they suffer some combination of devestation and invasion by trees from warmer climates? The latter seems more likely to me.
Also this week:
...discussed by Ed Yong.
...dIscussed by Ed Yong.