Plants evolved to “heat it up” at night, to attract insects

Plants have evolved alongside insects for millions of years now. This is all because plants need insects to pollinate them as soon as they flower. Therefore, there is strong selective pressure on this interaction between the two; it could almost be called an evolutionary relationship. Plants evolved flowers that are more attractive to the insects, and the insects find more ways of getting to the flowers and then pollinating them. An example is how flowers become more colourful and insects “learn” how to see these colours better. Even HEAT can become attractive for insects?! Researchers at the Department of Organismic and Evolutionary Biology and Museum of Comparative Zoology, Harvard University, Cambridge, found a mechanism in plants that attracts beetles with infrared radiation (heat!!). They found this in a subgroup of the Cycads. Cycads are a group of seed-bearing plants, often referred to as living fossils. They have existed surprisingly unchanged since the time of the dinosaurs. They look remarkably similar to palms, although they are not as closely related to each other as you might think.

Z. Furfuracae, our plant of interest today

Most plants are both male and female at the same time, but not the cycads; they have separate male and female plants. So the plants need the beetles to transfer pollen from the male to the female plants. They both have a sort of pinecone-like structure in them, which can be either male or female. The researchers found that in all sampled species, they could heat up and cool down these cones. Which happened differently throughout the night. It was shown that pollen (male) and ovulate (female) plants exhibited distinct circadian dynamics. This means that they either warmed up or cooled down differently on a day-night rhythm up to a whole three degrees above ambient temperature. Three degrees might not sound like a lot, but it’s quite an accomplishment for a plant that we normally see as pretty “cool”.  

Image showing a warm cone at night through an infrared camera

The beetle pollinators use specialized antennae to sense infrared; they detect this heat from a great distance. It was shown that the male cones of Z. Furfuracea (the plant of interest) heated first and then cooled down, whereas the female cones reached peak warmth only 3 hours later. This observation led them to investigate the relationship between the nightly increase in temperature and pollinator behaviour. This showed that the beetles first went to visit the male plants and picked up the pollen. Afterwards, the male plants cooled down, and they went on to find the female plants where the beetles deposited the package. It is quite extraordinary to see such coordinated behaviour, from an ancient plant no less.

The heat obsessed Beetle Rhopalotria furfuracea

The fact that these plants produce heat is interesting on its own. To put it in a nerdy way: They bypass the normal ATP metabolic pathway, and produce heat through alternative oxidase of carbohydrates and lipids or by uncoupling proteins. Previously, they only thought that the plants did this to create a “nice place” for insects and hoped for pollination that way. But now these researchers have shown this to be coordinated and conducted to a degree that an orchestra would be proud to get close to. From specific heat signatures to lure only these beetles, to the previously mentioned differences in male and female heat circadian rhythms, you can see that these cycads really try their best for eachother.

You could say these plants have “The Hots for each other”.