When flowers turn up the heat

July 28, 2010

Could a "hot" flower attract pollinators by serving as a reward in a plant-pollinator mutualism? Many flowering plants produce nectar and pollen as rewards in exchange for pollination services by insects and other animals. Interestingly, however, a few plants have flowers that also produce heat metabolically -- so what is the adaptive function of this flower heating?

Susanne Renner from the University of Munich, Germany and Shi-Xiao Luo from the South China Botanical Garden, along with collaborators from China and Taiwan, were interested in determining whether there was a connection between the heating of flowers and the pollination services of flies in an ancient Chinese family, Schisandraceae. Although this family is quite widespread, including Asia and the Americas, its center of diversity is in China, which is one reason Renner and colleagues chose to examine this question in two Chinese Illicium species. Their novel findings are published in the July issue of the .

"A few flowers, usually ones pollinated by beetles or flies, produce heat to help scent emission or to create especially attractive egg laying sites for their pollinators," Renner commented. "Usually such heating occurs only during flowering, simultaneous with the release of pollen and stigma receptivity. We discovered that in an Asian Illicium species, flowers reach their highest temperatures during early fruit development, and experiments revealed that this is for the exclusive benefit of the pollinator's larvae, which develop in the spent flowers."

Indeed, by combining diurnal and nocturnal observations of flower visitors with recordings of flower temperature from the onset of the female phase, through the male phase, and on through what the authors term the "nursing phase," Renner, Luo, and colleagues made a surprising discovery that the key stage of thermal warming was well after the flowers' sexual function is over.

By staying up for hours throughout the night, Luo observed that gall midges, belonging to a new species of Clinodiplosis, visit flowers in the male and female phases, carry pollen in on their bodies, and lay eggs on stigmas. At the end of the male stage, the flowers' stigmas fold inward and the styles move upright, forming a chamber around the midge eggs. It is during this "nursing phase" that the flowers produce the highest temperatures (about 2.5° C above ambient temperatures).

"Experiments revealed that heated tissues are essential for the development of the pollinators' larvae," Renner noted. When the tepal tips were trimmed, in the nurseries died, presumably because of the temperature drop, but seed development was not affected. "This implies a novel role for flower heating," says Renner. "An immediate lesson from this discovery is that heat monitoring should not stop with the end of a flower's attractive phase."

When the authors examined the pattern of midge pollination and flower heating in Schisandraceae within a molecular phylogenetic context, they concluded that flower heating is an ancestral trait, which likely first evolved to attract flies through increased odor emission. Midges subsequently may have taken advantage of the warm flowers for breeding, thus setting the stage for this exclusive mutualism.

Explore further: Flowers shape themselves to guide their pollinators to the pollen

More information: Luo, Shi-Xiao, Shu-Miaw Chaw, Dianxiang Zhang, and Susanne S. Renner (2010). Flower heating following anthesis and the evolution of gall midge pollination in Schisandraceae. American Journal of Botany 97(7): 1220-1228. DOI: 10.3732/ajb.1000077

Related Stories

Probing Question: Why are flowers beautiful?

January 24, 2008

In the 1930s, American artist Georgia O'Keefe wrote: "What is my experience of the flower if it is not color?" O'Keefe is best known for her vibrantly colorful close-ups of petals and stamens on large canvases.

New research explains orchids' sexual trickery

December 17, 2009

A new study reveals the reason why orchids use sexual trickery to lure insect pollinators. The study, published in the January issue of The American Naturalist, finds that sexual deception in orchids leads to a more efficient ...

Recommended for you

Genomes uncover life's early history

August 24, 2015

A University of Manchester scientist is part of a team which has carried out one of the biggest ever analyses of genomes on life of all forms.

Rare nautilus sighted for the first time in three decades

August 25, 2015

In early August, biologist Peter Ward returned from the South Pacific with news that he encountered an old friend, one he hadn't seen in over three decades. The University of Washington professor had seen what he considers ...

Why a mutant rice called Big Grain1 yields such big grains

August 24, 2015

(Phys.org)—Rice is one of the most important staple crops grown by humans—very possibly the most important in history. With 4.3 billion inhabitants, Asia is home to 60 percent of the world's population, so it's unsurprising ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.