In order to ensure pollination, leafflower trees in the genus Glochidion have entered into an intimate relationship with a small family of moths. Their flowers have become so specialized that no other insect is capable of pollinating them. In return, female moths are provided with an edible place to lay their eggs - the fruit of the tree. One species of leafflower has taken this relationship to the extreme. It holds its pollinators captive. In order to understand this bizarre relationship, we must first take a closer look at this interesting pollination syndrome.
Ecologists refer to this type of pollination syndrome as "brood pollination." In the case of the leafflower trees, pollination is achieved thanks to female moths known commonly as leafflower moths. Gravid female leafflower moths locate the blooms thanks to a special perfume tailored specifically for each species. The females first visit the male flowers where they pick up some pollen. Next they visit the female flowers where they will then deposit the pollen into a special chamber that can only be accessed by the female moths' proboscis.
After pollination, the female leafflower moth will then locate the ovaries of the flower and using a needle-like ovipositor, will deposit eggs within the undeveloped fruits. The larvae within eventually hatch right next to their food source - leafflower seeds. The larvae aren't gluttons. They will only eat one or two of the dozens of seeds developing within the fruit.
Although this may seem wasteful on the part of the plant, it makes a lot of sense from an evolutionary perspective. Essentially it reduces the likelihood that the moths will try to cheat the system. Gluttonous larvae that eat more than one or two seeds will be penalized and, in the long run, fewer seeds could equate to fewer host plants. By tying the reproductive abilities of the moth to the production of fruit, the tree ensures regular pollination.
For most of the leafflower/moth pairs, once the seed meal is over, the larvae chew out of the fruit and fall to the ground to pupate. However, this is not the case for a leafflower known scientifically as Glochidion lanceolarium. A native of southeastern China, it takes this relationship a step further by holding the larvae captive for nearly a year.
Cut open an fruit of this leafflower and there is a chance you might find a fully formed moth waiting patiently inside one of the swollen chambers. Instead of chewing out before it pupates, the moth is held captive within. Only when the fruits mature and split open will the moths be released. This happens just as the new crop of flowers is opening. The tree is literally controlling when its obligate pollinator is available to do its reproductive bidding.
The uniquely intimate nature of this relationship goes beyond simply being interesting. By studying how these two partners interact in relation to the other leafflower/moth partners around the Old World tropics researchers are gaining a better understanding of how such mutualisms evolve.
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