The existence of glossy surfaces in the plant and animal world poses a mystery to science. While clear and consistent signals are advantageous for reliable communication, such as between flowers and pollinators, glossiness contradicts this principle. Its appearance is highly dependent on the viewing angle and illumination conditions, making it variable and unpredictable.
A research team at Julius-Maximilians-Universität Würzburg (JMU) has investigated this contradiction. Their study reveals that gloss fundamentally alters the efficacy of visual signals depending on the distance and viewing angle of the observer, presenting both advantages and disadvantages.
The Science Behind Gloss: Surface Structure and Light Reflection
The study, led by Dr. Johannes Spaethe at the Chair of Behavioral Physiology and Sociobiology at JMU, alongside Dr. Casper J. van der Kooi from the University of Groningen and Alexander Dietz, was recently published in the journal Science Advances. The research delves into the microscopic surface structures that differentiate matte and glossy flowers.
“The difference between matte and glossy flowers lies in their microscopic surface structure,” explains Johannes Spaethe. Most flowers have a matte surface formed by countless tiny, cone-shaped cells, such as snapdragons, which scatter light in all directions, resulting in a stable color signal visible from almost every angle.
In contrast, glossy flowers like buttercups have flat surface cells that act like tiny mirrors, reflecting bright, directional flashes of light. These reflections can overlap or even overlay the actual color signal caused by the flower pigments.
Behavioral Experiments: Bumblebees and Artificial Flowers
To explore the impact of gloss on pollinators, the research team conducted behavioral experiments with bumblebees (Bombus terrestris). Using artificial flower replicas differing only in surface texture—matte or glossy—they precisely analyzed the insects’ reactions, revealing a fundamental visual conflict.
“The advantage of glossy flowers is that they are more easily recognizable from a distance,” explains Alexander Dietz. The gloss effect is particularly significant at the perception limit of bumblebees, at very small viewing angles between three and six degrees. Shiny flowers remained visible to the insects, while matte flowers of the same color and size could no longer be recognized.
However, there is a downside. “The same shine that attracts from a distance makes it difficult to perceive colors at close range,” notes Casper van der Kooi. Experiments showed that bumblebees struggled to distinguish between similar colors on shiny surfaces at close range. “The light reflected from the flat cells interfered with the reliable interpretation of the color signal,” he adds.
The risk of confusion has noticeable ecological consequences: for bees, foraging on glossy flowers becomes less efficient, requiring more time and energy to distinguish the correct flowers. For plants, there’s an increased risk of “interspecific pollen transfer,” potentially reducing reproductive success.
Evolutionary Implications: Balancing Visibility and Signal Accuracy
What does this compromise mean for the evolution of the plant world? “Glossiness appears to be an evolutionary strategy for certain ecological conditions where improved visibility from a distance outweighs the disadvantage of more difficult color recognition at close range,” says Johannes Spaethe.
However, the study also highlights why evolution has favored a matte surface in most flowers: it ensures a spatially consistent and reliable color signal through broad light scattering, enhancing pollinators’ ability to recognize and distinguish flowers accurately.
Interestingly, this conflict between recognizability and signal accuracy extends beyond the floral world. “Similar principles also play a role in predator-prey interactions,” says Alexander Dietz. For instance, the gloss of insect cuticles can hinder mantises and jumping spiders in accurately tracking their prey, while the flashes of light from fish scales may reduce the probability of birds successfully hunting them.
Looking Ahead: Future Research and Ecological Insights
The findings from JMU’s research team open new avenues for understanding the ecological roles of gloss in nature. Future studies could explore how these principles apply across different ecosystems and species, potentially offering deeper insights into evolutionary strategies.
As scientists continue to unravel the complexities of gloss in nature, the study serves as a reminder of the intricate balance between visual signals and ecological interactions. The ongoing exploration of these natural phenomena promises to enhance our understanding of the delicate interplay between organisms and their environments.
