About 3.7 billion years ago, a string of naturally occurring amino — the same kind that astronomers have found in meteorites and just recently in a stellar nursery near the center of the Milky Way Galaxy— reacted with a naturally occurring catalyst and began the fateful process of self-assembled replication. One of the most fascinating questions in biology is how these simple rogue molecules resulted in the endless pageantry of bizarre creatures that exist today. Charles Darwin did a lot of the legwork when he refined the idea that life changes over time. He reasoned that if you take two groups from the same species and keep them separated long enough (on the order of thousands to millions of years), they eventually evolve into distinct species of their own.
For the impatient, there's a faster way to make new species. Hybridization, for example, often does the trick, but this can get messy because of something called introgression and can still take hundreds of years to occur naturally.
Many plants, and a few other organisms, can expedite diversification even further by doubling their number of chromosomes. This process is called autopolyploidy, and under the right conditions, it can generate new diversity instantaneously.
There are numerous ways that autopolyploidy can take place, but the general idea is straightforward. Through one mechanism or another, the reproductive cells in a plant make an extra copy of their DNA. Both of these copies then get passed down to the plant's offspring, giving it two identical sets of chromosomes. The new plant can still reproduce with other plants that have the normal chromosome complement, but their offspring aren't likely to survive.
Biologists used to think this was merely an interesting aberration, that autopolyploids were rare in nature, and those that did exist had little chance of establishing a viable population. This later turned out to be false; autopolyploids are common and have a high rate of survival. Biologists also reasoned that autopolyploids would not be able to coexist with their parent species. The number of chromosomes being the only difference between them, the old and new species would be competing for the same resources, and one of them would eventually win out. If both were to exist, they'd have to do so in different places. They were wrong about that, too.
That's the subject of a new theoretical study on a humble plant called beetleweed (Galax urceolata), which has not two but three different chromosome complements, called cytotypes, throughout parts of its range in the Appalachian Mountains.
"Through my fieldwork, I discovered that a single population could have a mishmash of cytotypes, which fascinated me," said the study's lead author, Shelly Gaynor, who completed the work as part of her doctoral dissertation at the University of Florida. "With this study, I set out to understand if these populations could persist over time. Would one cytotype eventually outcompete the others, or could all three cytotypes persist?"
Visit the American Naturalist website to find out the answer, or get into the nuts and bolts by accessing the study directly.
Nicholas Kortessis and José Miguel Ponciano of the University of Florida and Douglas and Pamela Soltis of the Florida Museum of Natural History are also coauthors of the study.
