A. John, An enthusiasm for orchids: sex and deception in plant evolution

Abstract

Spring arrives in western Australia by the end of August and the shrubby vegetation is colorful and richly perfumed. Some native orchids, though, are brownish or dull-maroon in color, the human nose fails to pick up any fragrance. The strange shapes of the flowers give them such common names as warty hammers (Drakaea), flying ducks (Paracaleana), lazy spiders (Caladenia) and elbow orchids (Arthrochilus). While we smell nothing, these orchids release odors irresistible to many species of wasps. The winged males mistake sculptures and patterns on the lip petals for the bodies of virginal and wingless females. As a lovesick insect backs out of the flower, a plug of sticky pollen globs is deposited on his back. If the same wasp visits a second flower of the same species then cross-pollination occurs and seeds are fertilized although the deceived insect fathers no offspring during this process. More than 40 orchid species found in Western Australia fool male wasps. Why is pollination-by-deceit such a common ‘‘theme’’ in this part of the world? Why not ask Professor John Alcock of Arizona State University? He is known for his research in insect behavior and some past work took him to the southwestern corner of Australia. If you have read his past books such as In a Desert Garden and The Kookburra’s Song you know he can turn the study of evolution into an entertaining and enriching trip. The book is beautifully illustrated with close up photos of the deceptive flowers ‘‘at work.’’ Yes, you will see wasps humiliated by plants within one of the world’s most exciting hotspots of biodiversity. For any serious environmentalist, the chapter on conservation is disturbing. Past agricultural practices in western Australia have reduced available sites where rare species once flourished. They have also introduced European weeds, contributed to a saltier water table and spread an epidemic of cinnamon fungus (Phytophora), killing native species in its path. However, the greatest pleasure in Dr. Alcock’s book is his ability to relate his personal orchid rambles to the work of Charles Darwin. Many of us forget that Darwin turned to orchid pollination following the publication of his Origin of Species. He used orchids as ‘‘model systems,’ in two editions of a book he first wrote in 1862, so the general reader could understand how flower organs fused together and evolved adaptations to better exploit the insects that visit them and transfer their pollen. Consequently, Alcock’s book is most convincing as a study on the survival of the reproductively fit. There’s a nice, early chapter on how and why plants move (also indebted to some of Darwin’s studies on carnivorous and Cassia plants). This is particularly useful for readers, as some Australian orchids have jointed and cantilevered lip petals that flip and reposition male wasps before they have the opportunity to recognize the floral fraud. Let me emphasize, though, that this is not a pretty little adventure in nature appreciation. You will be asked to think early and often and this means reading slowly and thoughtfully. Alcock is one feisty author. He wrestles with the papers of Stephen J. Gould and Richard Lewontin that downplayed the role of adaptation in evolution. For his next trick, Alcock takes a healthy crack at the Creationist movement for still insisting that orchids are beautiful examples of plants created by a sudden act of ‘‘intelligent design.’’ Curiously, Alcock’s book convinced me that both reputable scientists, like Gould and Lewontin, presented arguments as flawed as the stuff published by the people who currently hide under the banner of Creationism. The simple, take-home message from this American in Australia is that, if you ignore the results of almost 160 years of published research and do not bother to P. Bernhardt (&) Department of Biology, St. Louis University, St. Louis, MO 63103, USA e-mail: bernhap2@slu.edu