Snapdragon secrets

Every season, scientists from the Institute of Science and Technology Austria (ISTA) go on field trips to the Pyrenees. Their mission: gather snapdragon flowers to understand their genetic makeup. In a recently published study in Molecular Ecology, they show how nature uses color genes to keep two varieties of snapdragons distinct, even when they share the same habitat. 

On the border between France and Spain lies a mountain range that spans from the Bay of Biscay to the Mediterranean Sea. The lush valleys and high peaks attract many tourists to the Pyrenees, known as “Pireneus” in Catalan.

Arka Pal, a biologist and PhD student from the Barton group at the Institute of Science and Technology Austria (ISTA), visits the region for a different reason. He comes to collect snapdragons or Antirrhinum—a vibrant plant that, when squeezed, resembles the jaws of a dragon. Together with an international team of scientists, Pal’s newest publication highlights the importance of flower color genes that keep two snapdragon varieties separated in several valleys across the Pyrenees, although they hybridize and occupy the same space.

Collecting snapdragons

For the past 17 years, scientists from the Barton group have been travelling to Planoles—a Spanish village situated 1,135 meters above sea level, near the Río Rigat and the French border—looking for snapdragons. Each field season, around 20 researchers reside in a small hut, venture into the picturesque surroundings and collect over 5,000 samples.

“You could romanticize it and say we are hiking,” Pal jokes. “But Antirrhinum likes to grow in human-disturbed habitats, often alongside mountain roads. So, we walk these beautiful roads in the Pyrenees, sporadically climbing steep slopes through brambles and nettles to collect snapdragons.”

When in bloom, snapdragons are easy to spot with their striking yellow or magenta petals. When they are not, the scientists rely on identifying their leaves. Pal and his colleagues keep records of the plants’ growth and their GPS locations, and collect both flowers and leaves for processing back in the hut. There they assess the color of their samples, score how much magenta or yellow they have, and take pictures of the flowers from different angles. Additionally, they dry the leaves in silica gel and put them in envelopes to bring them back to ISTA to genetically analyze them.

What drives the Barton group to invest such effort in studying these plants? What deeper insights into evolution does the color of a snapdragon reveal?

Hybrid zones – nature’s laboratory

Pal is interested in how speciation happens—how different varieties emerge from a common ancestor and separate over time. In the valley of Planoles, two varieties of Antirrhinum—distinguished by their vibrant yellow (A. majus striatum) and magenta flowers (A. majus pseudomajus)—come together and hybridize naturally. During the last ice age, the two Antirrhinum varieties were geographically isolated in different parts of the Pyrenees. As the ice melted, they likely gradually spread along the valley from opposite directions, forming a so-called ‘hybrid zone.’

“Hybrid zones are essentially ‘natural laboratories’ where you can study the process of speciation and evolution in nature, letting nature conduct the experiments for us instead of crossing them in greenhouses,” says Pal. The magenta and yellow snapdragons form a narrow strip, roughly 1 km in length, where they hybridize to produce a kaleidoscope of colors.

The genetic encyclopedia

Planoles is not the only hybrid zone in the Pyrenees. A very similar one also exists 100 km to the west, near the town of Avellanet. The Barton group collected samples there, too. In his latest study, Pal compared both hybrid zones to understand how evolution has shaped them. Back at ISTA, Pal analyzed the two sets of samples to see whether their genomes look the same.

“You can think of the genome as an ‘encyclopedia of words.’ Within this encyclopedia, there are billions of letters which make up thousands of words—our genes. Yet, only a few key ‘words’ are important to keep species or varieties separated,” says Pal.

“The same bee species pollinates both the yellow and the magenta species. Bees learn where to go to find nectar. On the magenta side, they visit magenta flowers, while on the yellow side, they frequent yellow ones,” Pal says. Hybrids do not attract as many bees due to their lack of distinct color contrast required for bees to learn, resulting in reduced fitness and fewer offspring.

For snapdragons, the key trait is the flower color, which attracts pollinators and is essential for survival and passing genes onto the next generation. Despite sharing most genetic ‘words,’ only a few critical genes—seven to be specific—determine flower color and remain unique to each species. These genes, with names as alluring as those of Pokémon, include Rosea, Eluta, Rubia, Sulfurea, Flavia, Aurina, and Cremosa.

Color genes eclipse proximity

To tackle this data set, Pal made use of whole-genomic sequencing—a tool commonly used to map the DNA of humans and other animals. In this case, he and his team employed a novel sequencing technique that had previously been untested for Antirrhinum. Unlike well-studied organisms such as mice or Arabidopsis thaliana plants, where more genomic data exists, this large-scale sequencing of snapdragon genomes involved a process that resembled piecing together a vast puzzle.

“When we compared the Planoles and Avallenet hybrid zones, we found their genomes were quite different—they all had different mixtures of ‘words.’ But the seven genes that control the flower color were the same in both zones,” explains Pal. Those genes, act like keywords that stay consistent.

In hybrid zones, one would expect nearby plants to be closely related to each other. But when the researchers traced the plants’ genetic ancestry, they discovered that the flower color genes did not follow that pattern. The seven genes in the yellow snapdragons from the Planoles zone were more closely related to those in the yellow plants in the Avellanet zone. The same was true for magenta plants too.   

Pal’s new study reveals that, although there is a lot of genetic variation between the zones, the genes responsible for flower color have a shared evolutionary history. This finding is important—it suggests these color genes help snapdragons remain distinct and recognizable, even when they grow in the same environment, and share other genes across their extensive genome.