Orchids: Nature's Con Artists and Codependents
Orchids are arguably the largest family of plants. Examples of the family Orchidaceae appear in virtually every climate on six continents. Yet, for all their survival prowess, orchids have proven for centuries to be among the most challenging flowers for botanists to cultivate. Moreover, even in the wild, orchids rely on a dazzling array of unique and specialized pollination strategies by which to reproduce. These ploys place many types of orchids at the mercy of a single partner species of insect.
For example, some orchids mimic the mating pheromones of bees. They draw in the male bees under false pretenses and then cover the insects with pollen. Similarly, certain orchids smell of rotting meat to attract carrion-feeding flies. In other cases orchids assume the color, shape, or fragrance of flowers that certain insects favor. Others mimic the appearance of enemy insects in order to provoke an attack. Once an insect has alighted, orchids bring to bear an arsenal of glue traps, escape tubes, or trap doors that forcibly coat visiting bugs in pollen. The pollen will then be carried to other orchids as part of the reproductive cycle.
While this partnership may seem forced on the insect by the orchid, in select cases the insect and the orchid have evolved together "willingly." In evolutionary terms, these most specialized orchids are prime botanical examples of a concept called coevolution. This theory describes how two species develop a symbiotic relationship wherein each evolves explicitly to benefit the other. As the process of coevolution progresses, each species becomes not only beneficial to but also utterly dependent on the other. In the case of some species of orchids, the plants need the assistance of a particular species of insect in order to reproduce. In such instances the insect also has evolved specifically to fulfill that function for the orchid.
The idea of coevolution between orchids and insects is nearly as old as the formal theory of evolution itself. Charles Darwin published his famous work On the Origin of Species in 1859 and spent the remainder of his life defending its evolutionary theories. As part of this ongoing debate over evolution, Darwin published another, less well known book in 1862. Entitled On the Various Contrivances by Which British and Foreign Orchids are Fertilized by Insects, the book recounts Darwin's observation of a certain species of orchid, Angraecum sesquipedale, native to Madagascar. It featured a nectar well 12 inches (31 cm) deep--far too deep for conventional moths or butterflies to tap. Darwin predicted the future discovery of a then unknown species of moth possessing the necessary physical attributes to tap this nectar. He also speculated that this moth plays a crucial role in the pollination of the deep-nectar orchid.
What made Darwin's supposition so outlandish was that in order to reach the orchid's nectar, the moth would need a 12-inch (30 cm) tongue. Such a physical feature seemed unlikely in a small insect. Yet roughly 40 years later, just such a species of moth was discovered. The moth was dubbed Xanthopan morgani praedicta, or the Predicta moth, by entomologists. It was so named to honor Darwin's prediction. The Predicta moth has a foot-long, strawlike tongue that can tap the Madagascan orchid's nectar. By doing so it in turn spreads the pollen of X. m. praedicta to other plants.
In exchange for this reproductive assistance, the moth enjoys the distinction of being the lone insect species that can reap the nectar of the orchid. This guarantees it an exclusive food source. The orchid's deep nectar well and the moth's tongue evolved in tandem. Each species benefits from the other, and each species depends on the other for its survival.
For example, some orchids mimic the mating pheromones of bees. They draw in the male bees under false pretenses and then cover the insects with pollen. Similarly, certain orchids smell of rotting meat to attract carrion-feeding flies. In other cases orchids assume the color, shape, or fragrance of flowers that certain insects favor. Others mimic the appearance of enemy insects in order to provoke an attack. Once an insect has alighted, orchids bring to bear an arsenal of glue traps, escape tubes, or trap doors that forcibly coat visiting bugs in pollen. The pollen will then be carried to other orchids as part of the reproductive cycle.
While this partnership may seem forced on the insect by the orchid, in select cases the insect and the orchid have evolved together "willingly." In evolutionary terms, these most specialized orchids are prime botanical examples of a concept called coevolution. This theory describes how two species develop a symbiotic relationship wherein each evolves explicitly to benefit the other. As the process of coevolution progresses, each species becomes not only beneficial to but also utterly dependent on the other. In the case of some species of orchids, the plants need the assistance of a particular species of insect in order to reproduce. In such instances the insect also has evolved specifically to fulfill that function for the orchid.
The idea of coevolution between orchids and insects is nearly as old as the formal theory of evolution itself. Charles Darwin published his famous work On the Origin of Species in 1859 and spent the remainder of his life defending its evolutionary theories. As part of this ongoing debate over evolution, Darwin published another, less well known book in 1862. Entitled On the Various Contrivances by Which British and Foreign Orchids are Fertilized by Insects, the book recounts Darwin's observation of a certain species of orchid, Angraecum sesquipedale, native to Madagascar. It featured a nectar well 12 inches (31 cm) deep--far too deep for conventional moths or butterflies to tap. Darwin predicted the future discovery of a then unknown species of moth possessing the necessary physical attributes to tap this nectar. He also speculated that this moth plays a crucial role in the pollination of the deep-nectar orchid.
What made Darwin's supposition so outlandish was that in order to reach the orchid's nectar, the moth would need a 12-inch (30 cm) tongue. Such a physical feature seemed unlikely in a small insect. Yet roughly 40 years later, just such a species of moth was discovered. The moth was dubbed Xanthopan morgani praedicta, or the Predicta moth, by entomologists. It was so named to honor Darwin's prediction. The Predicta moth has a foot-long, strawlike tongue that can tap the Madagascan orchid's nectar. By doing so it in turn spreads the pollen of X. m. praedicta to other plants.
In exchange for this reproductive assistance, the moth enjoys the distinction of being the lone insect species that can reap the nectar of the orchid. This guarantees it an exclusive food source. The orchid's deep nectar well and the moth's tongue evolved in tandem. Each species benefits from the other, and each species depends on the other for its survival.
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