Deceptive flowers exploit the behavior of pollinators using many different methods. Although there are many species that offer a legitimate reward, usually in the form of nectar, pollen, or other type of sustenance, there are many flowers (a large proportion belong to the genus Orchidaceae) that do not (Jersakova et al. 2006). How, and why, an organism is attracted to these deceptive flowers is a subject of study among scientists. This unidirectional exploitation of the senses, perceptions, and behavior of a pollinator is portrayed when a deceptive flower mimics a sight, smell, or touch associated with nourishment or copulation, in most cases, while not producing a reward, to the attracted pollinator who recognizes these inviting cues from past experiences with a model organism. This exploitation ultimately results in the transfer of pollen to the given conveyor, who then transfers these gametes to a stigma of a different plant of the same species, and eventual fertilization and production of offspring (Dafni 1984).
The life history of a flower is straightforward; the main objectives of a flower are fairly limited, as they are immobile throughout their lifetime. These objectives include reproduction, and survival. In order to survive, a flower must gain water, sunlight, and nutrition. In order to reproduce, a flower must have an effective method by which pollen is transferred from its anthers to the stigma of a different flower, in most cases. Most flowers transfer their pollen by simply by attracting a pollinator by using a reward, in the form of nectar, pollen, water, or other type of nourishing substrate (Herrera et al. 2002). Deceptive flowers use a variety of elaborate colorations, tactile representations, morphologies, and pheromones in order to attract pollinators (whether or not there is a reward) (Gumbert 2001). Not all flowers offer a reward to their pollinators; these deceptive flowers use a wide variety of methods in order to exploit the behavior of naïve pollinators.
A deceptive flower mimics the characteristics, which are found in a more recognized, abundant, and rewarding model. This type of mimicry is commonly referred to as Batesian mimicry. Flowers are also able to converge in order to mutually benefit, and in turn, mutually exploit the behavior of a pollinator (not always by the use of deception). This type of exploitation is commonly referred to as Muellarian mimicry (Schaefer et al. 2009). There have been over 7,500 species of angiosperms which have been categorized as deceptive, 6,500 of which are orchids (one-third of orchid species currently known) (Jersakova et al. 2006). The methods, by which the behavior of a pollinator is exploited, are primarily based in nutritive, and reproductive methods of deception.
Many species of deceptive flowers use reproductive mimicry in order to exploit the behavior of pollinators. For example, the orchid Ophrys fusca is able to mimic the olfactory, visual, and tactile cues associated with a female insect. These visual cues, most evident to the human eye, are effective only at moderate distances, and the tactile cues associated with these deceptive flowers are only effective once a pollinator has landed on the labella of a given flower. The effects of olfactory cues, in the form of pheromones produced by the osmophore glands of a deceptive flower, are the singular, most effective method, which attracts pollinators from long distances (Raguso 2005). This olfactory attraction is due to innate pollinator behavior and preset preferences for specific stimuli (Schiestl 2010). Pseudo-copulation occurs when a male pollinator (usually within the order, Hymenoptera) lands on this type of deceptive flower, and attempts to mate with what it believes to a female. While the male pollinator does not assist in producing offspring of its own species, the pollen (sometimes prepackaged in pollenia sacs) of the orchid is then transferred to the pollinator, who can then transfer these gametes which it has accumulated to another plant of a the same species where it attempts to copulate again. In this example of Batesian mimicry, the flower gains a reward, while the insect gains nothing (Jersakova et al. 2006).
Deceptive flowers can also imitate an oviposition substrate, where a pollinator (such as a dung fly) normally lays its eggs. These flowers are able imitate the olfactory cues associated with an oviposition site (a location where a female insect may lay her eggs). These smells are generally associated with dung, carrion, decaying organic matter, fermenting sugars, fungi, fruits, fish, or rotten flesh (Raguso 2005). Deceptive flowers are able to mimic these characteristics in order to attract female insects that are prepared to lay their eggs. For example, some species within the genus Stapelia are able to mimic the characteristics of carrion. Flowers of these plants are characterized by hairy trichomes, reddish-brown color, heat production, as well as the emission of a foul odor containing dimethyl disulfide, in association with other amines, in order to stimulate the oviposition of nearby female pollinators. The deceived insect will ultimately transfer pollen from the host (who is unable to support eggs that are laid), to another plant of the same species, in order to carry out fertilization. (Kunze et al. 2010).
In some instances, traps are used in order to restrict a pollinator, who has and landed on a deceptive flower, from leaving for one to five days. There have been over 3,000 species of angiosperms, which have been found to make use of traps in order to attract pollinators (Rodriguez-Girones et al. 2010). Many of these insects are attracted to these deceptive flowers for the same reasons as mentioned in the previous paragraph. Tactile cues, such as fungus-like structures that are present inside some traps, also play roles in attracting pollinators (Dafni 1984). Once inside a trap, there are also methods, which have been adopted by flowers, in order to ensure the safety of small fragile pollinators, and thereby, encourage pollination (in turn, the behavior of the pollinator is exploited). Arum italicum in a non-rewarding species that has been shown to produce an increase in temperature, once a pollinator has been trapped. It has been shown that this increase in heat is able to increase the attractive odors’ rate of production, and dispersal (Meeuse 1978). The production of heat allows some species of plant to penetrate a snow layer. This production of heat may also assist in the mimicry of feces or carcasses of dead animals (therefore attract pollinators, such as Flesh flies, searching for oviposition sites) (Herrera, 2002).
There are also species of blood-sucking insects that assist in the pollination of Arum conophalloids, Iin this species of flower; increased odor is associated not only with a raise in temperature, but also increased carbon dioxide production. These conditions are very similar to the set of stimuli, which attract Lucilia sericata (a species of carrion fly). The production of carbon dioxide also mimics the qualities associated with the symbiotic microorganism that live in feces, and produce carbon dioxide. Carbon dioxide also has the effect of relaxing pollinators, so that they do not become anxious while trapped within a plant for extended periods of time (Schaefer et al. 2009).
Light also plays a role in the attraction of flies to the anthers of a deceptive flower. The attraction of insects at the deepest location of a deceptive flower to a “window-pane” (surrounded by darker coloration) to the outside world, where anthers are located, also assists in the successful pollinator of a plant (this anomaly is commonly found in the family Taccaceae). Although these conditions are found in all species of plants that make use of traps, many of these physical stimuli are able to exploit the reproductive drives of pollinators, who can then play roles in the fertilization of deceptive flowers (Dafni 1984).
Deceptive flowers are able to mimic the nutritive anatomy of a rewarding flower, and in turn, exploit the behavior of pollinators. For example, some deceptive orchids are able to adopt floral signals such as color, scent, nectar guides, spurs, and other morphologically similar traits, which are found in rewarding flowers (thereby attracting a wide variety of naïve pollinators) (Dafni 1984). The orchid, Dendrobium unicum produces pseudopollen, which is composed of small hair like outgrowths sprouting from the surface of a plant. These outgrowths are generally unicellular, and globular (trichomes). Pollinators, mostly within the order hymenoptera, are drawn to this pollen- like substance predominantly due to its attractive color, and scent, even as it is inedible (Davies, 2004). False anthers are also produced in many genera of orchids (such as Caladenia). These fraudulent male reproductive structures consistently appear to be full of pollen, even when they are not, and are used to attract pollinators (Dafni, 1984). Pseudo-nectaries in deceptive flowers resemble the nectaries that produce nectar in rewarding flowers. However, these organs, which are well exposed on the surface of many species of the genus Parnassia, do not produce a reward (Carter 1999). Although these exploitative traits do not reward their pollinators, once a pollinator lands on one of these deceptive flowers, pollen is transferred to the guest, and in turn, is transferred to another plant (usually of the same species). Nutritive mimicry is very effective, and is the most common form of behavioral exploitation within the genus Orchidaceae (38 genus of orchids use this method of exploitation), partially due to this wide variety of behaviorally exploitative tactics (Jersakova et al. 2006).
Although less common, some species of deceptive flowers are able to mimic a shelter, which is suitable for housing a pollinating insect. This shelter can provide warmth, a place to sleep or rest, as well as protection during a meteorological event. For example, some species within the Mediterranean genus, Serapias, have inflorescences that are able to mimic the red-black pigmentation, which is associated with the dark entrances to bee nests. Although there are benefits to the pollinator in this situation, the resulting pollination of these flowers results in the exploitation of pollinator behavior (Jersakova et al. 2006).
Most of the pollinators of these deceptive flowers are bees (of the genus Maxillaria, or Eria). These pollinators generally emerge in early spring, are newly immigrated, or are dominant pollinators whose resources are decreasing in abundance. Research by Ackerman et al. 2011 showed the blossoming of many species of deceptive flowers is associated with pollinator arrival. Although a pollinator will likely learn to avoid a deceptive flower once it has been encountered, and found to offer no reward, these deceptive flowers survive, and monopolize on the behavior of a pollinator are consistently successful, in most cases (Johnson 2003).
Three preset conditions are required in order for a mimic to be successful. First, the mimic must be less abundant than the model organism. Secondly, the characteristic, which is being mimicked, must be well known to the potential pollinators. Thirdly, the model organism must counter-balance the behavior of the mimic, byut supplying a consistent reward. (Anderson 2005). If these tasks are achieved, a deceptive flower will consistently exploit the behavior of pollinators.
The reasons why flower mimicry is so rare vary greatly. Plants are static, and live in clumped formations, because of this, a pollinator can generally avoid an unrewarding patch of mimics, and in turn, drive down the abundance of these deceptive flowers. Henceforth, if a mimic is to be successful, it must be locally associated with its model. However, due to the capability of olfactory cues to widely disperse, mimic and model do not necessarily need to be within close proximity in order for both flowers to be successful. A more simple answer as to why mimics are rare was posed by Amots Dafni, who remarked that this rarity might originate in the faults of researchers who have overlooked these relationships between mimic and model throughout the past (Ackerman et al. 2011).
There are many methods, which are used by deceptive flowers in order to exploit the behavior of their pollinators. Although pollinators are able to discern the deceptiveness of a flower, these unique plants continue to reproduce, and survive by using of nutritive and, reproductive mimicry in order to exploit the senses, perceptions, and behavior of their pollinators.
