Living fossils of the plant world, the cycads can trace their lineage back to about 300 million years ago. In a world without flowers, forests of these palm-like plants were the main feature of the dinosaurs' landscape. Today the cycads (http://www.nybg.org/events/prel_landsc.html) are mere vestiges of their glorious past: an estimated 19 genera are known only as fossils and of the 11 living genera, most are on the verge of extinction because of loss of habitat, slow growth, and infrequent reproduction. In a joint project with Fairchild Tropical Garden, Dr. Dennis Wm. Stevenson, Director of the Harding & Lieberman Laboratories at The New York Botanical Garden and the world's leading expert on cycads, is studying their pollination biology. His work confirmed that cycads are pollinated by specific species of weevils (http://www.nybg.org/events/prel_weevil.html)and beetles and unravelled the symbiosis -- mutually beneficial relationship of two dissimilar organisms living together -- between plants and pollinators, demonstrating that the cycads' survival is contingent upon the preservation of their ecosystem. Pollination -- the transfer of the sperm-cell-loaded pollen from the male structure to the female structure for germination -- involves separate male and female cycad plants with reproductive structures called cones produced when both plants reach maturity. The pollen-laden male cone differs in shape, size, and color from the female cone. Dr. Stevenson's study of Zamia furfuracea (http://www.nybg.org/events/prel_2.html,) Zamia pumila, and Dioon califanoi showed that each cycad genus has its own genus of pollinators and each cycad species has its own species of pollinators. He uncovered a fascinating tale of plant/animal interdepedence where each participant follows a precise sequence of events and plays a specific role in order to ensure the propagation of both species. In this quid pro quo relationship, the insects perform the pollination and the cycads in turn offer the insects food, shelter, a breeding site, and larvae protection.
Dr. Stevenson found that in Zamia furfuracea (http://www.nybg.org/events/prel_1.html), for example, the pollination mechanism starts with the cycad adapting its weapons to the situation: The male cone, the insect brooding and feeding site, turns its defense down by sequestering most of its toxins, while the female cone (http://www.nybg.org/events/prel_4.html), unpalatable to the insects, disperses its toxins to prevent future seed predation. Ready to welcome the pollinators, the mature male cone emits heat and an aroma attractive to the insects, imitated by the female cone which also mimicks the male morphology; with no real incentive to offer,the female cone essentially disguises itself as a male to get the visit of the pollen-carrier insects. Out of the 15- 20 cones on a male plant, the insects select and swarm on the one or two which are ready to release the pollen, then feed and breed, carefully avoiding the plant parts that still contain diffused toxins. The insects use the sequestered toxins to make the larvae's cocoon, protecting the larvae from predators. The next insect generation, covered with pollen, flies from cycad to cycad, staying long enough on the female cones to spread the necessary pollen for germination. The pollinators even adjust to the 2- to 3-year reproduction cycle of the cycads as the end-of-the-season larvae conveniently go into a dormancy stage interrupted only by the mature cones' aroma of the cycads' next reproduction cycle. This age-old plant reproduction system beats all records of longevity and achieves a 100% fertility rate.
Principal Investigator: Dr. Dennis Wm. Stevenson, Director, Harding & Lieberman Laboratories
Public Relations: Annick Sullivan 718-817-8815
The above story is based on materials provided by New York Botanical Garden. Note: Materials may be edited for content and length.
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