What Is the Symbiotic Relationship of the Yucca Plant?
Yucca is a genus of plant that includes about 40 different species. Most of these plants grow in Mexico and the southwest United States, but a few species favor the less arid landscapes of the southeastern U.S. and the Caribbean islands. Yuccas of all varieties are dependent upon insects -- mostly moths -- for their pollination. This symbiotic relationship is mutualistic, meaning that it benefits both the plant and the insect. Does this Spark an idea?
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Yucca Plants
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Because of the shape of their flowers, plants in the Yucca genus cannot wind pollinate the way some other flowers do. Their receptive stigma are located deep in the flower, where wind-blown pollen will not reach. For an insect to properly pollinate a yucca plant, the pollen must be deposited inside a stigmatic depression, but the pollen of the yucca plant doesn't take the form of individual grains. Instead it clumps together, making it difficult for most inspect species to carry.
Yucca Moths
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There are two main species of yucca moth, Tegeticula and Parategeticula, and each pollinates the yucca. While some moths are host-specific and favor a particular species of yucca, others have been found to pollinate different species. Female yucca moths have a special adaptation of the jaw that includes maxillary palpi. She uses these prehensile palpi to collect up to a dozen clumps of pollen (called pollinia), which she then makes into a ball. Once she's collected the pollen, she deposits her eggs into the wall of the yucca's seed chamber, and pushes in the pollen.
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The Caterpillars
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The young yucca moths hatch inside the walls of the seed chambers and begin to hollow out seeds and bind them together with its silk. From inside its protective area, it feeds on the yucca's seeds into the fall. During the autumn rains, after the seeds have been released, the caterpillars come out of their seed "cocoons" and drop to the ground. They burrow under the soil, create a true cocoon from their silk, and there they wait out the winter.
Mutualistic
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This process helps both species, which makes it a mutualistic symbiotic relationship. Not only does the yucca get pollinated, but the eggs that the moth deposits hatch inside the plant. The yucca's seeds provide the hatched caterpillars with food, but they don't eat so much of the seeds that they harm the yucca's reproduction. Not all such relationships are beneficial to both parties, and the level of dependency between the yucca plant and the yucca moths is remarkable because both depend on the other for their propagation and survival.
Timing
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For this cycle to continue and for both species to propagate, timing is important. The young yucca moths must emerge when the yucca plants are blooming so they have somewhere to lay their eggs after mating. To adapt to this, some caterpillars will hibernate two or more years, waiting to emerge until there are enough yucca blooms to provide for their needs.
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References
- Photo Credit yucca image by Terry Reimink from Fotolia.com
