Often, when unrelated angiosperm species utilize the same groups of animals for pollination, their flowers will exhibit similar characteristics. For example, moth-pollinated flowers tend to be white colored with long nectar tubes. They typically open in the evening, exhibiting strong, sweet smelling odors and offering relatively large amounts of nectar.
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| Image: Charles Hedgcock |
The mutualistic relationship between an angiosperm and its pollinators presupposes that selective pressures exhibited by the pollinators will choose for floral traits that favor the most effective and abundant pollinators. Consequently, flowers pollinated primarily by moths open in the evening because moths are nocturnal feeders. Odor tends to be potent in these flowers because moth orientation in the low light levels of the evening relies more heavily on non-visual cues. Long nectar tubes are also favored in these flowers because they allow the plants to reserve their rewards for only able pollinators, like moths, who can reach the nectar source with a lengthy proboscis. And because metabolic rate is astoundingly high in these insects, moth-pollinated flowers offer plenty of energy-rich nectar to compensate for the costs of flight.
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| Image: Jiao-Kun Li and Shuang-Quan Huang |
When flowers rely on a specific group of animals for pollination, we refer to this as a
specialized pollinator mutualism. Often in these plants, floral traits are indicative of the specific mutualism, in which case these collective floral characteristics are termed a
pollination syndrome.
In contrast, some flowers do not have specialized relationships with particular pollinators. These species rely on a group of generalized insects to carry out their pollination activities. In such circumstances, floral traits are selected for not by a single dominant pollinator, but by the combined influence of all the acting pollinators. Floral traits in these species consequently do not favor a single type of pollinator, and cannot be characterized by a "pollination syndrome." When flowers are pollinated by a broad group of insects, we call this a
generalized pollination system.
For example, in the Asian sacred lotus flower (right), scientists observed bees (A,B), beetles, (C,D), flies (E), and thrips (F) all visiting the same flowers.
