"Oh I've heard about you! You're the guy who does the whatchamacallits, you know, MacGyverisms; turns one thing into another?"
Do you remember the American TV series MacGyver? The other day, by chance I found a very interesting paper published recently in Science explaining an amazing co-evolutionary event in a tropical plant, Marcgravia. After reading it, I automatically thought: Marcgravia is the MacGyver of pollination! Turns one thing into another… Want to know why?
Marcgravia is a plant genus belonging to its own hidden family, Marcgraviaceae, only found in the New World Tropics (Central and South America). The group is relatively small and the flowers not well studied. However, their inflorescences are pretty extravagant. The inflorescences consist on upside-down umbels with several flowers hanging down. The flowers have 4 or 5 petals fused together (characteristic of Ericales clade, where they belong to) and the number of stamens is highly variable and showy. Not a very exciting description, right? Yep, that’s because the excitement of these flowers remain on the bracts and bracteoles – and now you are asking: “What are those?”. Bracts and bracteoles (small bracts) are leaf-like structures associated with the inflorescences (bracts) and individual flowers (bracteoles). Bracts and bracteoles are sometimes associated with the protection of the flower, but in many cases they don’t have any particular function, so some plants might lack them. In Marcgravia we can find both structures and both of them have a good reason to exist.
The bracteoles of Marcgravia are a piece of art! They were modified into big and exuberant pitcher-shaped nectaries, imagine big nectaries full of yummy nectar… Lucky pollinators! Oh yeah, and who pollinates these amazing flowers? Any guess? Well… It actually depends, but such big structures with large quantities of nectar are definitely not pollinated by invertebrates… They are pollinated by big animals, mainly humming birds and bats. Actually, the reason why I wanted to tell you this story is because of the amazing co-evolution of pollination between Marcgravia evenia and bats. Just like MacGyver, using common things to make complex gadgets, Marcgravia evenia also made quite a gadget with their bracts. How? By turning a boring leaf-like structure with apparently no use (the bract) into an echo-location device!
The inflorescence bracts of Marcgravia evenia developed into a dish-like structure, guiding the bats in the forest into the inflorescences! The shape of the bract produces a strong and easily recognizable echo by the bats, making it easier for the bats to find the inflorescences. Once they find the inflorescence, they feed on the nectar inside the pitcher-like nectaries (the modified bracteoles); the hanging flowers (with numerous stamens which are full of pollen ready to be released) are strategically positioned, leaving the bat’s back full of pollen and this is how pollination happens in this species. Actually, this system is highly efficient, since the bats take only half of the time to find flowers with these bracts in comparison to other flowers without them.
So Marcgravia is for me like MacGyver, turning things with no apparent use into very usefull ones: bracteoles into pitcher-shaped nectaries and bracts into echo-location devices… Isn’t Nature absolutely amazing?