Cycads use heat to lure beetles. This ancient relationship offers new insights into the co-evolution between plants and their pollinators.
Not colours and scents, but heat lured the first pollinators to ancestral forms of seed plants. Cycads possess specially adapted mitochondria and circadian genes for rhythmic heat production in their pollen cones, whilst specialised beetle species have infrared-sensitive TRPA1 receptors in their antennae that make this remarkable co-evolution possible. This is the finding of research on the cardboard palm (Zamia furfuracea) and its associated pollinating beetle Rhopalotria furfuracea (Science, 12 December). A pollination relationship that has existed for 200 million years, and evolutionary comparisons show that this heat- and infrared-based signalling is older than the now widespread pollination signals based on scent and colour.
The researchers, led by evolutionary biologist Wendy Valencia-Montoya of Harvard University – who received part of her training in Groningen – established that this cycad produces a single daily heat pulse that begins in the afternoon and peaks in the early evening. Male pollen cones warm up three hours earlier than female cones. This is sufficient for a nocturnal sequence of visits by pollinating beetles following the infrared trail. By using a signal detectable by only a single receptor, cycads may have become locked into a nocturnal moonlit dance with beetles that constrained their evolutionary radiation, write British plant scientists from the University of Cambridge in an accompanying perspective. The success of flowering plants was made possible by pollination from diurnal insects, which are guided primarily by scents and colours.