How Do Orchid Flowers Adapt to Pollination?
Insects, such as the highly specialized orchid bees and the long-tongued hawkmoths, pollinate the myriad species of orchids that dominate the tropical regions surrounding the equator. However, due to varying circumstances, some orchids relegate their pollination process to other methods and must therefore make modifications in both their pollinating mechanisms and nectar production. Does this Spark an idea?
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Types of Change
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Most of the orchids in Madagascar are white, have nectar and long-spurred flowers that give off a heavy scent during the evening and night hours to attract moths, especially the long-tongued hawkmoth. However, three species have morphed into unscented short-spurred flowers that open in the morning hours to attract birds instead.
These adapted orchids, like other bird-pollinated flowers, have multi-flowered inflorescences featuring fleshy, unscented, short-spurred, reddish flowers. The orchids evolved to have a narrow opening at the top of the nectar sac containing a lip with a strong fold that only opens when a bird pecks against it.
Orchids that attract birds produce more diluted nectar than insect-pollinated orchids
Orchids that are pollinated by birds make the texture of its pollen stickier and larger so that it adheres to the bird's beak, which prevents self-pollination and prevents it from being removed when the bird preens.
According to C. Micheneau, in the "Annals of Botany" all orchid flowers in the archipelago with spurs longer than 3 1/2 inches have developed reproductive means totally independent of pollinators and subsequently autonomously self-pollinate.
Reasons for Change
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Orchid pollination adaption may be a result of low density of moths and insects in the region. Changes also occur when the orchid population becomes so dense that the local insect population cannot suffice. Insect populations become scarce for night or winter-blooming species of orchids.
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Other Pollinators
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According to the C. Micheneau study, the adaptations of orchids in Madagascar's Mascareme Archipelago allow the white-eyed Zosteropoidae bird to pollinate them. Some orchids in the South American Andes Mountains, where insects are scarce, have adapted to the region's high diversity of hummingbirds. Sunbirds in South Africa pollinate orchids in that country, as do honeyeaters in Australia.
Environmental Factors
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When orchid species become isolated from their continental relatives, they morph into more specialized adaptations in both their breeding and pollination systems, and availability of local possible pollinators often becomes a major driving force. For example, the orchids on the Madagascar archipelago can reproduce without the aid of pollination, but fruit can only develop after the plant has been pollinated. Therefore, enticing local fauna becomes important but not necessary for survival.
Results of Adaptations
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Fruit production of orchids pollinated by birds remains about the same as insect-pollinated species. Birds that feast upon orchids have a steady diet. Adaption also allows orchids to thrive in areas that had been previously unsustainable for them, and heavy populations of orchids no longer compete with each other for pollinators, which causes large populations to thrive.
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References
Resources
- Photo Credit orchid image by pncphotos from Fotolia.com
