科研之友
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摘要
Plant species sometimes exhibit dynamic contrasting patterns in terms of reproductive traits. Floral colour change - the retention of old, non-productive, rewardless, but fully turgid flowers in an altered colour - has been considered as a plant strategy for enhancing pollinator attraction while minimizing visits to non-reproductive flowers. Considering the perceptive and cognitive abilities of animals, these advantages should apply in most systems. It seems paradoxical, and therefore, that floral colour change occurs in only a portion of angiosperms. This divergence may be explained if floral colour change adds as yet unknown costs or benefits under specific conditions. To explore such possibilities, we compared details of trait combinations and pollination consequences between a floral colour-changing (Weigela coraeensis) and a non-colour-changing (Weigela hortensis) species in a shared environment. Flowers of W.coraeensis secreted nectar for initial 2-3days and remained white, after which they persisted for a few more days with discoloured, red purple petals and reduced nectar levels. Flowers of W.hortensis also secreted nectar for initial 2-3days. They persisted for a few more days with the same colour and reduced amounts of nectar, but did so only when pollinators were scarce. Because only W.hortensis suffered from pollination difficulty at our site, both species retained their flowers for 4-5days. Bees strongly preferred to visit W.coraeensis, leading to a greater proportion of seed set than in W.hortensis. In addition to their higher nectar productivity, only W.coraeensis plants offered bees colour difference as a visual cue to choose rewarding flowers and improve both long-term and short-term rates of nectar intake. By learning where to return, bees apparently responded to the difference in resource exploitability. Results indicate that floral colour change yields an additional benefit of attracting bee-like pollinators that return preferentially to more easily exploitable plants. Under conditions where benefits of enhancing both conspicuousness and exploitability cannot outweigh the costs of doing so, however, retention of rewardless flowers in the same colour and flexibility in floral longevity - as was adopted in W.hortensis - may become more advantageous in terms of saving metabolic and ecological costs.
- 出版日期2014-6
