Wild snapdragons paint themselves in subtle shades to attract bees

Wild snapdragons have evolved to subtly adjust their coloration to better attract bees, according to new research published in Science Advances. A team led by scientists at the John Innes Centre, in collaboration with researchers in Austria, China, and Australia, discovered that the flowers use a combination of genetic factors to fine-tune their hues. This adaptation helps them stand out to pollinators while maintaining energy efficiency in their growth. The study focused on wild snapdragons (Antirrhinum majus), which exhibit variations in flower color depending on their geographic location. In particular, the researchers examined a unique hybrid zone in the Pyrenees mountains, where two distinct varieties of the plant meet. One variety features yellow flowers with a magenta spot, serving as a visual cue for bees to locate the nectar-rich center. The other variety displays magenta flowers with a yellow spot, creating a complementary signal. These contrasting patterns suggest an evolutionary arms race between the plants, each striving to outcompete the other in attracting pollinators. The researchers identified seven genes responsible for controlling the coloration of the flowers. Three of these genes regulate the production of magenta pigments, while four govern the development of yellow tones. By studying the interactions among these genes, the team found that the subtle differences in color, barely perceptible to humans, are crucial for bees. The study revealed that the variation in yellow shade is achieved through a complex interplay of four genes, which collectively shape the gradient of color across the petals. In the hybrid zone, where the two varieties interbreed, the resulting flowers often display unusual color combinations, such as orange or white. These hybrids are less effective at attracting bees compared to the purebred varieties. As a result, natural selection has acted to keep the area of genetic mixing extremely limited, confined to a narrow strip just 1 kilometer wide. This restriction allows scientists to measure the selective pressures acting on individual genes, offering insights into how evolution shapes complex traits. Dr. Desmond Bradley, the study’s first author, explained that the research highlights how small genetic changes can lead to significant ecological advantages. “Even patterns that are nearly invisible to us can be detected by bees,” he noted. “These tiny shifts in color help the flowers compete more effectively in the pollinator marketplace.” The findings underscore the precision with which natural selection operates, even when the effects of individual genes appear minimal. The implications of the study extend beyond snapdragons and bees. Molecular gradients, similar to those observed in the flowers, play a critical role in many biological processes, from the formation of butterfly wings to the development of fruit fly embryos. Until now, it remained unclear how natural selection influences such gradients or whether it targets individual genes or groups of genes. This research provides a framework for understanding how multiple genetic factors contribute to the refinement of complex traits. The discovery adds to a growing body of evidence showing that evolution is driven by intricate mechanisms, often operating at scales too small for human perception. By examining the subtle interplay of genes in wild snapdragons, the study reveals how nature continuously refines its designs to ensure survival and reproductive success.