Short and Tall Plants: One Has Speedier Evolution Than the Other

Some creatures evolve more quickly than others. For example, the ancient coelacanth has changed hardly at all for millions of years, while plants are constantly changing. Now, researchers have discovered that short plants actually evolve faster than taller ones.

In order to examine the rate of evolution in plants, the researchers looked at a database of global patterns in plant height for more than 20,000 species. They were able to estimate the average maximum height for nearly 140 plant families worldwide. The families ranged from tropical plants called the Brumanniaceae, whose average height tops out at two inches, to a family called the Tetramelaceae, which can tower at 140 feet.

After finding out the average heights of these families, the researchers then estimated how much their DNA sequences changed over time. They then plotted these evolutionary rates against plant height. Their findings were surprising.

It turns out that shorter plants evolved as much as five times faster as taller ones. In fact, the pattern held up for both the nuclear and chloroplast genomes, even after the researchers accounted for factors shown in previous studies to correlate with evolutionary speed (like species richness). The results also held up when they looked just within trees and shrubs, which are typically tall, or just herbs, which tend to be short.

There's a reason why shorter plants evolve faster, though. The difference is probably driven by genetic changes that accumulate in the actively-dividing cells in the tip of the plant shoot as it grows. Since cells down copy their DNA perfectly each time they divide, this can encourage evolutionary changes.

"Genetic changes that occur during cell division in plant shoots could potentially get passed on to future generations," said Robert Lanfear, one of the researchers, in a news release.

Growth actually slows when plants increase in size. This means that over the long term, the rate of cell division and genome copying in taller plants eventually slows down. This, in turn, decreases the possibility for changes in the DNA.

The study reveals that the evolutionary rate for plants is certainly not the same over all species. In addition, it reveals an interesting correlation between height and evolutionary growth.

The findings are published in the journal Nature Communications.