When we think of evolutionary changes, we tend to consider long stretches of time. But can evolution happen rapidly? There is some evidence that yes, evolutionary changes can occur quickly. New research reported in Current Biology has highlighted an example of a permanent biological change that took place in a relatively short period of time, in a flower called the Colorado blue columbine. One population of this flower carries a version of a gene that's caused the plants to drop their petals, which are known by their spurs of nectar. Though a lack of spurs isn't unheard of for these flowers, it happens a lot more than usual in this group of plants, with about a quarter of them lacking the distinctive spurs.
Scientists knew that spur development was affected in part by a Colorado blue columbine gene called APETALA3-3. The researchers found that the development of spurs and nectaries is controlled entirely by this gene. The change is straightforward, because the gene is either on or off, "but that simple difference causes a radical change in morphology," said lead study author Zachary Cabin. One mutant gene will produce a plant that lacks petals or spurs.
There is no gap between these two morphological states in the fossil record either. The researchers suggested that this is evidence for rapid evolutionary changes.
"This finding shows that evolution can occur in a big jump if the right kind of gene is involved," said senior study author Scott Hodges, a professor at the University of California Santa Barbara. When the APETALA3-3, which directs an organ to become a petal, is turned off, a totally different organ, called a sepal, is produced instead.
APETALA3-3 can direct the development of a whole organ as one example of a homeotic gene. When mutations arise in a homeotic gene, an organism's biology can be dramatically affected in crippling ways. But, in rare instances, such changes can be beneficial somehow. Those major, rapid, beneficial changes would stick around with the carrier, and could be passed on to future generations.
Genetic changes like these, which don't happen slowly, can be difficult to catch in action. But now that researchers have an example, they can learn more about the processes that are at work.
The researchers found that there are five variants of APETALA3-3, and only one will produce a petal with a nectar spur that functions normally. The other four versions of the gene don't function normally. But as long as the plant carries one copy of the normal gene, it will develop normally. When any two mutant versions come together, the gene doesn't function as it should.
Previous work by this research team has indicated that nectar spurs are important to columbines, so the scientists wondered why so many of the flowers lost them, but still survived and did fine. It seems that for this flower, success depends on more than just attracting pollinators. Mutant plants were found to generate more seeds than other plants, surprising the researchers.
Caterpillars and aphids can cause damage that interferes with seed production, Cabin explained, and the whole plant might suffer. The researchers found that deers and aphids were more likely to visit flowers with nectar spurs. Thus, herbivores were influencing the change in the flower, and not pollinators.
"Natural selection can come from very surprising sources," Hodges said. "It's not always what you'd expect it to be."