Large Patterns for Hungry Bumblebees
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Imagine being a flower that needs to be pollinated and therefore needs to attract as many pollinators as possible. Now imagine being a bumblebee that, in a short time, must collect nectar from as many suitable flowers as possible. Surely, the bumblebee cannot move randomly among flowers hoping to find the right ones—that would be a waste of energy. At the same time, the flower must develop characteristics that attract specific pollinators.
Until recently, it was thought that bright colors and the scent of nectar were the main causes of pollinator attraction. But there seems to be more to it: hidden bullseyes in flower patterns play a significant role in attracting bees.
How did this discovery come about? Previous research had identified specific transcription factors and enzymes responsible for producing petal pigments and surface textures, but the initial processes that divide the petal epidermis into two distinct regions remained a mystery.
To understand the process, a group of researchers developed a method to dissect, prepare, and observe tiny hibiscus petals under a microscope. They discovered that, in the early stages of development, the petals have about 700 greenish cells, without the typical purple pigmentation and without differences in cell shape or size. As development progresses and the petal reaches 4,000 cells, purple pigmentation is still not visible, but a specific region appears where the cells are larger than their neighbors: this is the pre-pattern. These cells mark the position of the bullseye boundary—the line on the petal where the color changes from purple to white. Without a boundary, there's no bullseye. And without a bullseye? No pollination.
Using computational models, the scientists also discovered that the hibiscus can modify the size of the bullseye very early in the pre-patterning phase by regulating cell expansion or division later in development. This process determines the development of different colored regions, including the purple bullseye that attracts bumblebees.
So, what's the relationship between these essential insects and the hibiscus? Bumblebees have a clear preference for larger bullseyes and were also 25% faster in visiting flowers with larger bullseyes. This preference increases the efficiency of both bees and flowers; flight requires a lot of energy, and if a bumblebee can visit more flowers in less time, it's advantageous for both the insect and the plants.
The precision of natural designs plays a crucial role in the survival and evolution of species. Hibiscus trionum, for example, with larger bullseyes, likely attracts more pollinators, increasing its reproductive success. Species like Hibiscus richardsonii, on the other hand, are considered vulnerable and endangered, perhaps because they have small bullseyes and are less chosen by pollinators. Enhancing our knowledge of these floral patterns can help develop strategies to increase pollinator visits, which is fundamental for the success of crops that depend on pollination.
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