Flowers such as hibiscus rely on an unseen blueprint created early in their petal development that determines the size of their distinctive markings—known as bullseyes. This essential design plays a significant role in attracting pollinating bees.
Flowers such as hibiscus rely on an unseen blueprint created early in their petal development that determines the size of their distinctive markings—known as bullseyes. This essential design plays a significant role in attracting pollinating bees.
A recent study from researchers at the University of Cambridge’s Sainsbury Laboratory revealed that bees show a preference for larger bullseyes compared to smaller ones. Additionally, they fly 25% faster between artificial flower discs that feature larger bullseyes, potentially making their foraging more effective for both the bees and the flowers.
Patterns on flowers serve as guides for bees and other insects, directing them toward the center where nectar and pollen are available, thus enhancing the plant’s chances of successful pollination. Despite their importance, the precise mechanisms behind the formation of these petal patterns and their evolution into the diverse forms we see today—like spots, stripes, and bullseyes—remain poorly understood.
The research utilized a small hibiscus plant as a model, examining closely related species with the same overall flower size but with bullseye patterns that varied in size. Those included H. richardsonii (small bullseye at 4% coverage), H. trionum (medium bullseye at 16%), and a transgenic version of H. trionum (large bullseye at 36% coverage).
It was found that the foundational pattern on the petal’s surface is established very early during the flower’s development, long before the petals display any visible color. The petal essentially acts as a ‘paint-by-numbers’ template, where different areas are predetermined to develop unique colors and textures even before they distinguish themselves visually.
The findings indicate that plants can accurately control and adjust the shape and size of these patterns through various mechanisms, which may have implications for plant evolution. By refining these designs, plants might achieve a competitive edge in attracting pollinators or start to draw in different insect species.
This research appears in Science Advances.
Dr. Edwige Moyroud, head of the research team exploring the mechanisms of petal pattern formation, noted: “If a trait can be developed through multiple methods, it offers evolution a broader range of options to modify it, leading to greater diversity, much like an artist with a wide palette or a builder with a vast array of tools. Our investigation into how bullseye patterns develop aims to clarify how nature fosters biodiversity.”
Lead author Dr. Lucie Riglet analyzed hibiscus petal patterning by studying the development in the three types of hibiscus flowers, each with the same overall size but differing bullseye patterns.
She discovered that the pre-pattern starts off as a small crescent-shaped area long before the bullseye becomes visible, even on tiny petals measuring less than 0.2mm.
Dr. Riglet stated: “At the earliest stage we examined, the petals consist of about 700 cells and are still a greenish color with no visible purple pigment or discrepancies in cell shape or size. As the petals continue to develop to 4000 cells, they remain without visible pigments, but a specific area was identified where the cells are larger than those surrounding them. This indicates the pre-pattern.”
These larger cells are crucial as they establish the boundary for the bullseye, marking where the color transitions from purple to white—without this boundary, no bullseye exists!
A computational model developed by Dr. Argyris Zardilis provided further insights. By merging computational models with experimental findings, the researchers demonstrated that hibiscus can adjust bullseye dimensions early in the pre-patterning phase or alter growth in different bullseye regions by managing cell expansion or division later in the development.
Dr. Riglet then evaluated the effectiveness of the bullseye patterns in attracting pollinators using artificial flower discs that simulated the three distinct bullseye sizes. Dr. Riglet mentioned, “Bees not only preferred the medium and larger bullseyes over the small size, but they also visited the larger discs 25% faster. Foraging is energy-intensive, so if a bee can visit four flowers in the same time it takes to visit three, it is likely beneficial for both the bee and the plants.”
The researchers believe that these pre-patterning strategies may have deep evolutionary roots, potentially impacting the variety of flower patterns across different species. The next goal for Edwige Moyroud’s team is to identify the signals responsible for generating these early patterns and to explore whether similar pre-patterning processes occur in other plant parts, such as leaves.
This research not only enhances our understanding of plant biology but also underscores the intricate relationships between plants and their environments, illustrating how precise natural designs are crucial for the survival and evolution of species.
For instance, H. richardsonii, which features the smallest bullseye among the hibiscus species studied, is critically endangered and is native to New Zealand. In contrast, H. trionum is not considered native to New Zealand but is widely distributed across Australia and Europe, and it has become a naturalized weed in North America. Further studies are required to ascertain if the larger bullseye contributes to H. trionum’s ability to attract more pollinators and improve its reproductive success.
