Specialized Plant Pollination Systems
Table of Contents Orchids 1 Ophrys 2 Pollination 3 Euglossine Bees 4-5 Generalization & Specialization 6 Co-Evolution 7 Museum Collections 8 Visual Deception 9 Chemical Deception 10 Alkenes 11 Morphological Variation 12 Orchid & Euglossine Databases 14 Project: Create a New Specialized Orchid System
Other Examples of Specialized Pollination Systems
References 17, 18
The Orchid What Are Orchids? “Orchids are a family of Monocotyledons. They have, like other Monocots, a single seedling leaf and their floral parts in threes. Orchids are one of the largest families of flowering plants, challenging the daisy or sunflower family, the Asteraceae (Compositae), for the title of the largest of all families. Currently there are known to be 25,000 species of orchids and estimates, based on the current rate at which new species are being discovered and described, suggest that the number may reach 30,000.”2
“What then unites these diverse plants into the family called the Orchidaceae? The distinctive features of orchids which separate them from other flowering plants lie primarily in their flowers.”2 1
Ophrys “The genus Ophrys is a large group of orchids from the alliance Orchis in the subtribe Orchidinae. These plants are remarkable in that they successfully reproduce through pseudocopulation, that is, their flowers mimic female insects to such a degree that amorous males are fooled into mating with the flowers, thereby pollinating them.”4
“They are referred to as the “Bee orchids” due to the flowers of some species resemblance to the furry bodies of bees and other insects. Their scientific name Ophrys is the Greek word for “eyebrow”, referring to the furry edges of the lips of several species.”4
“Most plants attract animal pollinators to their flowers by offering nectar, pollen, or edible floral parts to these mutualists. A small but significant number of angiosperm species offer other kinds of rewards...“specialized” rewards. Yet other species offer no rewards at all, instead deceiving their pollinators, eliciting visitation without any compensation whatsoever.”6
How Flowers Attract Pollinators Rewards or “Primary Attractants” “...constitute the primary or economic motivation for animals to visit flowers.”6
•Nectar •Pollen •Food Bodies
Advertisements or “Secondary Attractants” “...attract the attention of pollinators and promote associative learning.”6
•Bright Floral Displays •Distinctive Flower Shapes •Strong, Characteristic Fragrances
Euglossine Bees The Ophrys orchids typically cater to alluring male Euglossine bees. The tribe Euglossini has five genera and around two hundred species. “Euglossine bees, also called orchid bees, are the only group of corbiculate bees whose nonparastitic members do not all possess eusocial behavior.”8
“Within the astonishing diversity of orchid pollination systems, sexual deception is one of the most stunning.”9 To see the psuedocopulation pollination process in action, click here
BBC Video on Bee Orchids
Male Euglossine Bees â€œMale insects invest more time and energy in mating behaviour than females, which spend more time feeding and collecting food for brood care. Therefore, females are generally considered as more efficient pollinators. Whole guilds of plants, however, are specialized for pollination by males bees...â€?9
Whereas food-seeking female bees are more efficient pollinators, males conduct longer-distance visits and thus contribute relatively more to outcrossing... Collectively, pollination by male bees may be advantageous by mediating specific and long-distance pollen flow, and selection may thus favour floral signals that attract primarily males.â€?9
Generalization & Specialization “The dichotomy between generalization and specialization in pollination systems is a simplification, for purposes of debate, of what is really a continuum between plants pollinated by literally hundreds of pollinator species and those pollinated by just one pollinator species.”13
“Specialized pollination can be defined as an ecological phenomenon in which a flower species is pollinated by one or a few species or functional groups of animals (“ecological specialization” or flower pollination). Ecological specialization of the pollinator similarly refers to it visiting only one or a few flowers for food or resources...Floral specialization refers to flowers and flower features that limit the diversity of animals that can visit and pollinate the flowers...Finally, evolutionary specialization of plant-pollinator relationships refers to the evolutionary processes that increase ecological specialization, generally (but not necessarily) in response to specializing selection. This process presumably generated nearly all extant specialized plant-pollinator relationships.”13
Co-Evolution There is debate regarding the varying degrees of specialization and generalization amongst the numerous species of orchids. Understanding the benefits and disadvantages of both of these evolutionary trends, as well as the specific guiding causes, is a goal for current research. The benefits of specialization, which is typically the norm in the Ophrys orchids, include fidelity and loyalty from a very specific group of pollinators. In addition to garnering loyal pollinators, specialized systems may help prevent the stigma of the flower from becoming overloaded with pollen. Selective pollinators can reduce the potential for too much pollen distributed on the stigma, thereby clogging the stigma and impeding pollination.
Museum Collections How do scientists determine varying degrees of specialization or generalization within the genus Ophrys or other orchids? In order to study the systems of pollination with orchids, scientists are able to look at pollen found on male and female Euglossine bees in museum collections and match that pollen to particular species of orchids. By using museum specimens of bees as well as museum specimens of pollen slides, scientists can study the characteristics of the pollination systems occuring in the natural world. Museum specimens and databases can offer a better understanding of the complexity throughout these pollination networks.
There has been speculation on the influence of the visual characteristics of sexually deceptive orchids. For example, questions have arisen concerning the significance of the role of the ultra-violet or irridescent quality of some Ophrys that optically attract visitors. Further study may elucidate the varying degrees of visual sexual deception in conjunction with the more prominant allure of chemical deception. 20
Food for Thought: Do you think certain species rely on visual attractants more or less than other species that may rely more or less on chemical attractants? Or is it a well-paired combination? 9
Chemical Deception “The evolution of floral odour compounds mediating pollinator attraction is of general interest and can help us to understand evolutionary mechanisms in pollination systems. A relatively well understood pollination system is sexual deception in the European genus Ophrys, where mechanisms of pollinator attraction involve the mimicry of alkene patterns of female bees to sexually attract the male pollinators.”9 “Until now it was, however, unclear whether the biosynthetic ability to produce these compounds represents an evolutionary novelty of Ophrys within subtribe Orchidinae. In our approach, combining phylogeny and chemical ecology, we found that the production of alkenes is widespread among related orchids. Besides that, other species primarily pollinated by male bees produce similar high amounts and diversity of alkenes as Ophrys. Thus, alkene production itself is likely a plesiomorphic character in Ophrys, having evolved earlier than the pollination syndrome of sexual deception. We suggest that production of alkenes is an example of a preadaptation that evolved from a primary vegetative to reproductive function and enabled the orchids to exploit various behavioural patterns of their pollinators through chemical mimicry.”9 Food for Thought: What do you think evolved first -- mechanisms for chemical attraction of pollinators or mechanisms for sexual deception of pollinators? 10
“...specific patterns of nalkenes (unsaturated hydrocarbons) play a key role in orchids of the genus Ophrys (Orchideae, Orchidinae) for the attraction of male pollinators to the flowers.”9
Mean (+s.e.m) sum (ng/mm2)
“Sexual mimicry, or sexual deception, is well known in Europe, Australian, and Neotropical orchids, and is likely more widely distributed than currently known. This pollination system functions primarily through the species-specific imitation of female sex pheremones, in combination with less specific visual and tacile stimuli produced by the flowers.”9 11
Moths, beetles, flies
Absolute amounts of alkanes (black bars) and alkenes (grey bars) in orchid groups with contrasting pollinators9
Morphological Variation Given the vast number of species and sub species within the genus of Ophrys, there is an immense amount of variation. The causes of such variation result from numerous factors, several of which have yet to be further researched. Potential contributions to such diversity include geographic location, habitat, and co-evolutionary factors.
left: variation within Ophrys fusca right: variation within Ophrys sphegodes
Orchid & Euglossine Databases For an amazing resource with thousands of herbarium specimens, pictures of living plants, and drawings, explore the Swiss Orchid Foundation Click here to go to the Swiss Orchid Foundation
Another incredible resource with thousands of images of living plants of the Ophrys orchids can be found at the Reproductive Biology of Orchids’ database with 440 genera and 2373 species Click here to go to the Reproductive Biology of Orchids’ Ophrys Image Database To search for more resources on orchids, look at the Ophrys specimens at the JSTOR Plant Science database. Click here to go to the JSTOR Plant Science website To explore the taxonomy of Euglossine bees that pollinate other species of orchids, visit the Smithsonian Tropical Research Institute Click here to go to the Smithsonian Tropical Research Institute’s Taxonomy of Euglossines
Given the array of visual variation amongst Ophrys and the Euglossine bees, think of a new flower that is attracting a new or different kind of visitor --- What would your creation look like?
Other Specialized Plant Pollination Systems
Interested in other examples of specialized plant-pollinator relationships? Check these out or search for others!!
Long-tongued fly species Moegistorhynchus longirostris4
A female fig wasp, Tetrapus americanus, is about to enter a flowering fig, Ficus maxima
Crassula coccinea ...pollinated exclusively by the large satyriine butterfly Meneris tulbaghia”4
Xanthopan morgani, a hawk moth that pollinates Angraecum sesquipedalia 30
Upiga virescens moth, the pollinator of Pachycereus schottii, the senita cactus
Babiana ringens, the “Rat’s tail” plant, being pollinated by Nectarinia famosa, a malachite sunbird
References 1. DanBoy. “Ophrys vernixia.” Photograph. Orchid a Week by Dan. 5 Feb. 2011. Web. 30 April 2012. 2. Cribb, Phillip. “What Are Orchids?” Royal Botanic Gardens, KEW; Swiss Orchid Foundation at the Herbarium Jany Renz, 2005-2012. Web. 8 April 2012. 3. “Ophrys sphegodes Bianca subsp. atrata (RCHB.F.) E.Mayer.” Image. Swiss Orchid Foundation. 1868. Web. 30 April 2012. 4. “Ophrys.” Wikipedia, The Free Encyclopedia. 25 Mar 2012. Encyclopedia of Life. Web. 9 April 2012. 5. Image. <http://farm4.static.flickr.com/3371/3525514204_22abb4f0b9.jpg>. Web. 9 April 2012. 6. Patiny, Sebastien. Evolution of Plant-Pollinator Relationships. Cambridge: Cambridge University Press, 2011. Web. 1 March 2012. 7. Gerlach, G. “Ophrys passionis.” Photograph. Reproductive Biology of Orchids. 30 April 2006. Web. 30 April 2012. 8. “Euglossini.” Wikipedia, The Free Encyclopedia. 15 Jan. 2012. Web. 30 April 2012. 9. Schiestl, Florian P. and Salvatore Cozzolino. “Evolution of Sexual Mimicry in the Orchid Subtribe Orchidinae: The Role of Preadaptations in the Attraction of Male Bees as Pollinators.” BMC Evolutionary Biology, 2008. Web. 1 March 2012. 10. Vereecken, N. “Ophrys lupercalis.” Photograph. Reproductive Biology of Orchids. 5 March 2006. Web. 1 May 2012. 11. adrien2008. “Ophrys cretica ariadnae (pollinisator Melecta sp.).” Photograph. Flickr. Web. 30 April 2012. 12. Vereecken, N. “Ophrys arachnitiformis.” Photograph. Reproductive Biology of Orchids. 3 May 2006. Web. 30 April 2012. 13. Johnson, Steven D. and Kim E. Steiner. “Generalization Versus Specialization in Plan Pollination Systems.” Tree 4 April 2000: 140-143. Print. 14. Kretschmar, H. “Ophrys fusca () Kreutz.” Photograph. Swiss Orchid Foundation. 15 May 1997. Web. 30 April 2012. 15. perillimatteo. “Ophrys conradiae con insetto impollinatore.” Photograph. Flickr. Web. 30 April 2012. 16. Miller, Kelly. Photograph. Museum of Southwestern Biology. 2 May 2012.
References Continued 17. Ellenbast, F. “Ophrys mamosa DESF. ssp. mamosa.” Photograph. Reproductive Biology of Orchids. 26 April 2008. Web. 30 April 2012. 18. Gerlach, G. “Ophrys speculum.” Photograph. Reproductive Biology of Orchids. 30 April 2006. Web. 30 April 2012. 19. Kruetz, C.A.J. “Ophrys sphegodes Mill. subsp. aesculapii (Renz) Soo Ex. J. J. Wood.” Photograph. Swiss Orchid Foundation. 20 April 2000. Web. 30 April 2012. 20. Kreutz, C.A.J. “Ophrys fusca () Kreutz.” Photograph. Swiss Orchid Foundation. 18 March 2000. Web. 30 April 2012. 21. Baumann, H. “Ophrys sphegodes (Devillers-Tersch. & Devillers) Kreutz.” Photograph. Swiss Orchid Foundation. 15 April 1993. Web. 9 April 2012. 22. Kreutz, C.A.J. “Ophrys lutea ()Kreutz, M.R. Lowe & Wucherpf.” Photograph. Swiss Orchid Foundation. 22 March 2000. Web. 30 April 2012. 23. Renz, J. “Ophrys x subfusca Hausskn.” Photograph. Swiss Orchid Foundation at the Herbarium Jany Renz. 1926. Web. 30 April 2012. 24. Nelson, E. “Ophrys sphegodes Mill.” Image. Swiss Orchid Foundation. Web. 30 April 2012. 25. Renz, J. “Ophrys fusca Link.” Photograph. Swiss Orchid Foundation at the Herbarium Jany Renz. 25 March 1926. Web. 9 April 2012. 26. Paterson-Jones, Colin. Photograph. Biodiversity Explorer. Web. 30 April 2012. 27. Woodhall, Steve. “Aeropetes tulbaghia (Table mountain beauty, Mountain pride) male, Sehonghong.” Photograph. Biodiversity Explorer. Web. 30 April 2012. 28. Ziegler, Christian. Photograph. Cornell Chronicle. 27 Jan. 2010. Web. 30 April 2012. 29. Dimijian, G. Photograph. Holland Lab. 9 June 2011. Web. 30 April 2012. 30. Imamori, Mitsuhiko. Photograph. Smithsonian.com. 2008. Web. 30 April 2012. 31. Bruce, Anderson. Photograph. Animal Planet Interactions. Web. 30 April 2012. 32. Jean bes. “Adrena/Oph.marmorata_Ophrys marbre.” Photograph. Flickr. 9 April 2010. Web. 8 May 2012.