How flowers use colour to signal their scent

A team from Australia, Greece, Denmark, and the USA identified the relationship among many insect-pollinated plant species growing in a scrubland habitat on the Greek island of Lesbos.

The study, the first to demonstrate colour-fragrance integration for an entire plant community, found that the link between colour and fragrance was strong enough to be regarded as a combined signal.

Associate Professor Adrian Dyer from the School of Media and Communication at RMIT said: “We knew that flowers around the world had often evolved colours to suit the ultraviolet-blue-green vision of bees but no one knew how scent might be related. 

“By studying a natural habitat with many bee pollinators, we see that holistic understandings of signal-receiver relationships are very complex and require multisensory information transfer for effective communication.

“This evolutionary evidence may hold important lessons for how we can better use information processing in complex conditions.

The flowers often use coordinated signals of colour and fragrance to attract insects, which acquire pollen during floral visits and thus facilitate pollination of the plants. 

“In turn, the insects benefit from floral visits by acquiring nectar and pollen as food. As these processes are better understood we can improve management of natural resources for nature and agriculture.”

Dyer said the flowers connected visual and olfactory channels to make their signal to bees stronger and more stable under intense environmental conditions.

On windy days, fragrances dissipate but colours do the attracting, whereas fragrance can be the primary attractant when flowers are hidden among the dense vegetation of the Phrygana scrublands.

The researcher team, led by Dr Aphrodite Kantsa, designed a “social network” that illustrated the relationships between 41 plant species and 351 fragrance compounds emitted by them. 

The network proved to be highly complex and consisted of seven smaller modules of chemically similar plants. 

One module featured red flowers dominated by waxy, long-chain hydrocarbon scents. Another module contained plants with purple-pink flowers that emitted distinctive fragrances from another hydrocarbon class (sesquiterpenes) common to mints and sagebrush.

Kantsa said the plants in these groups were only remotely related, so the common occurrence of fragrances and colours did not reflect common ancestry but might reflect selective pressures by bee pollinators.

The research has been published in the journal Nature Ecology & Evolution. 

Story: David Glanz