Cold-blooded critters like insects need to heat up their bodies before they can do much of anything. But whereas snakes and lizards lie in the sun, new research finds that some insects bask in the warmth of ... plants. The plants attract their pollinators by literally producing hothouse flowers.
About 900 plant species worldwide (among them the well-known skunk cabbage) are known to produce heat in their flowers, says biologist Roger Seymour of the University of Adelaide, Australia. The heat, generated by an as yet unknown mechanism, was always thought to help disperse scents that beckon pollinating insects. Although this is certainly true, Seymour and colleagues show in a report in this week's issue of Nature that heat also may act as an incentive for the bugs that fertilize the flowers.
The researchers studied the tree-dwelling Philodendron solimoesense from French Guiana, which is pollinated by the scarab beetle Cyclocephala colasi. To avoid having to climb trees, the team chose places where trees had been knocked over during road construction. Hanging small data-loggers inside the flowers, they found that the flowers generate heat during the night, maintaining temperatures around 27°C, about 4° warmer than outside. Their scent attracts the beetles, which arrive en masse to feast on the pollen, fertilizing the flower in the process.
Next, the team looked at the energy requirements of feeding beetles. They did this by placing them in a so-called respirometer, which records the energy used by the animals. They discovered that at ambient night temperature, the beetles require two to five times more energy to keep their bodies warmed-up than inside the balmy floral chamber. For small beetles like C. colasi, says Seymour, "keeping warm is enormously expensive, because they lose heat so quickly." When the plants provide the heat, the insects can devote more energy to feeding and reproduction. So it's no wonder the insects spend 90% of their time in their comfortably heated flowers.
The new study is elegant, says ecologist Olle Pellmyr of the University of Idaho, Moscow, who studies insect pollinators and the rewards plants give them. He adds that future work should try to find out whether flowers with central heating indeed get more out of their pollinators than cold ones.