Researchers have discovered a link between floral colour and scent in a Mediterranean scrubland.
An international research team investigated 41 insect-pollinated plant species growing in a Phrygana scrubland habitat on the Greek island of Lesbos, and the way the plants communicate with the diverse insect pollinators in the same community. They discovered a link between the colour of the flowers and their fragrance, such that these two characteristics could be regarded as one united signal.
This is the first study to demonstrate colour-fragrance integration for an entire plant community, its findings published in Nature Ecology & Evolution.
The flowers use co-ordinated signals of colour and fragrance to attract insects, which acquire pollen during floral visits and ensure pollination of the plants. In turn, the insects benefit by acquiring nectar and pollen as food. By connecting visual and olfactory channels, the flowers render their signal stronger and more stable under the intense environmental conditions of the location. On windy days, fragrances may dissipate but colours will remain viable floral attractants, whereas fragrance could be the primary attractant when flowers are concealed by the dense vegetation of the Phrygana scrublands.
The researchers constructed a “social network” that illustrated the relationships between the 41 plant species and 351 fragrance compounds identified from the fragrances of these plants. The resulting network consisted of seven smaller modules of chemically similar plants. Nearly all of these modules could be characterized by specific odour-colour combinations.
For example, one module featured red flowers dominated by waxy, long-chain hydrocarbon scents. Another contained plants with purple-pink flowers that emitted distinctive fragrances from a hydrocarbon class (sesquiterpenes) common to salvia, sagebrush and other aromatic herbs.
The plants in these groups are only remotely related, so the common occurrence of fragrances and colors does not reflect common ancestry. Instead, the authors suggest these patterns reflect adaptive compromises between pollinator attraction and other pressures, such as environmental stress and defense against enemies. The biochemical and genetic links between floral pigmentation and scent production remain poorly understood, so it is unclear whether colour-odour combinations conserve energy for plants or reflect genetic factors that facilitate their integration.
The study provides a new direction for research on the interactions between plant signals and animal senses.