Wednesday 27 May 2015

On That Note...

The plant kingdom has an overwhelming number of species many of which have become specialised to their localised environments. An extraordinary adaptation many have developed is mimicry of other organisms in the local ecosystem to achieve pollination or protection. We have discussed many of these deceptive mechanisms over the past 11 weeks. The complexity of each mechanism is astounding. From the protective deception of Lithops to the olfactory mimicry of carrion and pheromones, the variety of mimics we have discussed provides an interesting look into convergent evolutionary tactics.
Perhaps one of the most fascinating families we have looked at is the Orchidaceae, which comprises the most complex and numerous forms of mimicry in the plant kingdom. The orchids have coevolved to attract and rely upon one or few species of pollinators, which involves the development of species-specific olfactory, visual, and tactile cues.
One of the most important pieces of information these co-evolutionary relationships provide, in all examples we have discussed, is the interdependence of organisms within ecosystems. If these plants rely on one or few species to pollinate, as many do, then it is important to realise the detrimental effects disturbance of these ecosystems can have. If, for instance, humans attempt to control certain insect species we perceive as pests, and these insects serve an important pollinating role, many species could suffer.
Lastly, it is important to realise that all of the information researchers have obtained so far is infinitesimally small compared to what is unknown. Many mechanisms behind mimicry and deception, particularly related to evolutionary origin, are poorly understood. It is also good to note that analysis of relationships from a human perspective can be flawed. Though it is all well and good to recognise these relationships as fascinating, many of these co-evolutionary relationships are of vital importance to the balance of the respective local ecosystem. It is my hope that researchers do and will continue to keep this in mind.

The Bulbophyllum Genus

Many species of wild orchids have myophilous, or fly pollinated, flowers (Tan et al., 2002). The genus Bulbophyllum (Orchidaceae) has flowers that produce a foul-smelling or sweet-smelling scent to attract flies (Van der Pijl and Dodson, 1969). Bulbophyllum (Orchidaceae) is probably the largest orchid genus and contains about 1000 species (Vermeulen, 1991). The Bulbophyllum flowers selectively attract male fruit flies of several Bactrocera species (Tephritidae) (Tan, 1998). After attracting flies by the fragrance it releases, Bulbophyllum flowers ensure the removal and deposition of the pollinarium by its floral lip, which has been modified and adapted to a well-balanced structure of hinged see-saw lip that provides a floral mechanism to assist in pollination by flies (Tan et al., 2002).

Bulbophyllum nudda

Males that feed on the substances produced by these flowers, phenylpropanoids, selectively store the intact chemicals or their metabolites in the rectal glands and release them during the courtship period (Nishida et al., 1993). These compounds are known to boost the pheromone and defense systems of male flies (Tan and Nishida, 1996) while also increasing mating success, thereby greatly benefitting the males of these species (Tan and Nishida, 2000).


Bactrocera cucurbitae

Acquisition of the phenylpropanoids may have evolved initially in the context of sexual selection, particularly female preference for males scented with chemicals derived from flowers (Nishida et al., 1997). In terms of coevolution between fruit flies and plants, these phenylpropanoids may mark the point at which divergence of natural fruit fly attractants occurs in the plant kingdom (Tan and Nishida, 2000). On the contrary, it may be a result of manipulation of the phenylpropanoid molecule by the plant to “convergently” attract multiple fruit fly species in a complex tropical ecosystem (Tan and Nishida, 2000).







References
Nishida R, Iwahashi O, and Tan KH 1993, “Accumulation of Dendrobium superbum (Orchidaceae) fragrance in the rectal glands by males of the melon fly, Dacus cucurbitaeI,” Journal of Chemical Ecology, vol. 19, pp. 713–722.
Nishida R, Shelly TE, and Kaneshiro KY 1997, “Acquisition of female-attracting fragrance by males of Oriental fruit fly from a Hawaiian lei flower, Fagraea berteriana,” Journal of Chemical Ecology, vol. 23, pp. 2275–2285.
Tan KH 1998, “Behaviour and chemical ecology of Bactrocera flies,” The Fifth International Symposium on Fruit Flies of Economic Importance, June 1–5, 1998, Penang, Malaysia.
Tan KH and Nishida R 1996, “Sex pheromone and mating competition after methyl eugenol consumption in the Bactrocera dorsalis complex,” Fruit Fly Pests—A World Assessment of their Biology and Management: Proceedings, IV International Symposium 1994, St. Lucie Press, Delray Beach, Florida.
Tan KH and Nishida R 2000, “Mutual reproductive benefits between a wild orchid, Bulbophyllum patens, and Bactrocera fruit flies via a floral synomone,” Journal of Chemical Ecology, vol. 26, no. 2, pp. 533–546.
Tan KH, Nishido R, and Toong YC 2002, “Floral Synomone of a Wild Orchid, Bulbophyllum cheiri, lures Bactrocera Fruit Flies for Pollination,” Journal of Chemical Ecology, vol. 28, no. 6, pp. 1161-1172.
Van Der Pijl L and Dodson CH 1969, Orchid Flowers—Their Pollination and Evolution, University of Miami Press, Miami, Florida, 214 pp.

Vermeulen JJ 1991, Orchids of Borneo, vol. 2—“Bulbophyllum,” Bentham-Moxon Trust, Toihaan Publishing Co. and The Sabah Society, Kota Kinabalu, Sabah, Malaysia, 342 pp.

Photos
Bulbophyllum nudda courtesy of orchids-flowers.com
Bacterocera cucurbitae courtesy of National Bureau of Agricultural Insect Resources at nbair.res.in

Monday 25 May 2015

The Dracula Genus

Dracula is a genus of unusual orchids that occurs in the moist and shady montane cloud forests of tropical America (Endara et al., 2010). Comprising approximately 148 mostly epiphytic species, Dracula can be found mostly in pristine forests and less frequently in disturbed habitats from southern Mexico to Peru (Luer 1993). The genus Dracula belongs to the most diverse subtribe of Neotropical orchids, the Pleurothallidinae, which comprises 5 to 8% of the floristic diversity of the Neotropics (Jørgensen & León-Yánez, 1999), and are a mostly fly-pollinated group (Pridgeon et al. 2001, Pridgeon 2005). This particular genus produces flowers that look and smell like small mushrooms (Dentinger et al., 2010). Most of these orchids exhibit a peculiar morphology of the lip-like lowermost petal of the flower that resembles the reproductive surfaces of gilled mushrooms (Luer 1993; Kaiser 2006). Dracula are thought to mimic mushrooms for deceptive pollination by “fungus gnats” seeking places to lay their eggs.


Some of these orchids even produce scents reminiscent of fungi (Kaiser 1993, 2006). Chemical analysis of scents trapped from greenhouse-grown flowers show they are dominated by the "typical flavour compounds of mushrooms" (Kaiser 1993:31, Kaiser 2006). This scent development likely came about via evolutionary experimentation, but once proved successful, became an important part of the Dracula reproductive ecology. It has also been observed that these flowers grow in similar habitats to the mushrooms being mimicked, further confusing the “fungus gnats” (Dentinger et al., 2010). Though debated whether this example represents true mimicry, given the spectacular resemblance of Dracula flowers in appearance, fragrance, timing, and location to mushrooms, as well as the empirical observation that they are pollinated by fungus-seeking flies, this seems to be a exactly that (Dentinger et al., 2010). Once again, this deception between flower and pollinator creates a fascinating basis for the study of co-evolutionary relationships.





References
Dentinger BTM and Roy BA 2010, “A mushroom by any other name would smell as sweet: Dracula orchids,” McIlvainea, vol. 19, no. 1, pp. 1-13.
Endara L, Grimaldi DA, and Roy BA 2010, “Lord of the Flies: Pollination of Dracula orchids,” Lankesteriana, vol. 10, no. 1, pp. 1-11.
Jørgensen PM and  Léon-Yánez S 1999, Catalogue of the Vascular Plants of Ecuador, Missouri Botanical Garden Press, St. Louis, Missouri, USA.
Kaiser R 1993, The Scent of Orchids: Olfactory and Chemical Investigations, Elsevier Science Publishers, Amsterdam, The Netherlands.
Kaiser R 2006, “Flowers and fungi use scents to mimic each other,” Science, vol. 311, pp. 806-807.
Luer CA 1993, “Icones Pleurothallidinarum X,” Systematics of Dracula (Orchidaceae), Missouri Botanical Garden Press, St. Louis, Missouri, USA.
Pridgeon AM 2005, “Dracula,Genera Orchidacearum, vol. 4 – Epidendroideae (Part One). Oxford University Press, Oxford, United Kingdom.
Pridgeon, AM, Solano R, and Chase MW 2001, “Phylogenetic relationships in Pleurothallidinae (Orchidaceae): combined evidence from nuclear and plastid DNA sequences,” American Journal of Botany, vol. 88, pp. 2286-2308.

Video courtesy of Jacky Poon from jackypoon.org

Tuesday 19 May 2015

Caladium steudneriifolium

Leaf variegation is widespread in different genera of Araceae (Croat, 1994). Variegated leaves are characteristic of many species of Angiosperms, in particular among understorey herbs in tropical and temperate forests (Givnish 1990). The partial loss of photosynthetically active surface in variegated leaves affects absorption and utilization of light and, therefore, net photosynthesis, and as a consequence growth and reproduction (Soltau et al., 2009). The existence and relative success of variegated leaf colour forms within Caladium steudneriifolium populations, therefore, implies that there have to be particular selective pressures that support variegation despite the energetic handicap compared to plain leaves (Smith 1986).

Leaves of Caladium steudneriifolium. (a) Plain leaf. (b) Plain leaf with an infestation of leaf-mining moth larvae. (c) Variegated leaf. (d) Plain leaf painted with white correction fluid in a pattern mimicking the natural variegation. From Soltau et al. 2009.


In the case of Caladium steudneriifolium, the colour patterns are predicted to act as classical Batesian mimicry. Soltau et al. observed that the whitish areas of variegated leaves strongly resemble the leaf damages caused by the larvae of mining moths. This suggested that the colour patterns of the variegated leaves mimic these damages to escape oviposition by adult female moths. Among other chemical, tactile or visual cues, insects can visually detect and assess previous infestation during the process of host plant selection (Lev-Yadun and Inbar, 2002). Soltau’s study showed that in the presence of herbivores, leaf variegation can be of high selective advantage despite the loss of photosynthetically active leaf area compared to plain leaves (2009). As such, these plants provide a strong basis for the study of coevolution between plants and herbivores, and the mechanisms underlying predator-avoidance adaptations. 









References
Croat T 1994, “Taxonomic status of neotropical Aracea,” Aroideana, vol. 17, pp. 33–60.
Givnish TJ 1990, “Leaf mottling: relation to growth form and leaf phenology and possible role as camouflage,” Functional Ecology, vol. 4, pp. 463–474.
Lev-Yadun S and Inbar M 2002, “Defensive ant, aphid and caterpillar mimicry in plants,” Biologial Journal of the Linnean Society, vol. 77,pp. 393–398.
Smith AP 1986, “Ecology of a leaf color polymorphism in a tropical forest species: habitat segregation and herbivory,” Oecologia, vol. 69, pp. 283–287.
Soltau U, Dotterl S, and Liede-Schumann S 2009, “Leaf variegation in Caladium steudneriifolium (Araceae): a case of mimicry?” Evolutionary Ecology, vol. 23, pp. 503-512.

Saturday 9 May 2015

The Australian Mistletoes

The Australian Loranthaceae comprise 64 species in 11 genera. A feature of Australian loranthaceous mistletoes is the close vegetative similarity, especially of the leaves, between many species of mistletoe and their usual hosts (Barlow and Wiens, 1977). The parasitic relationship often involves several dominant Australian genera of host trees such as Eucalyptus, Acacia, and Casuarina, and a number of mistletoe genera, including Amyema, Lysiana, Muellerina, Diplatia, and Dendrophthoe (Barlow and Wiens, 1977). Like other plant and animal parasites, mistletoes live in an intimate association with their hosts and derive nutrition from the host, and, of course, share a life-long association with a single host individual (Norton and Carpenter, 1998).

Needle-leaved Mistletoe. Photo: David Watson
           The Australian mistletoes show considerable variation in host specificity that makes for an interesting topic of study (Norton and Carpenter, 1998; Barlow and Wiens, 1977). Several species have very low host specificity and occur on many hosts of considerable taxonomic diversity (Norton and Carpenter, 1998). In tropical forest habitats, high host specificity is not likely advantageous because species dominance in the forest is low. There is likely selective pressure for the physiological capacity to infect and grow on a wide range of host species (Barlow and Wiens, 1977). On the other end of the spectrum, however, there are species of Australian mistletoe that are specific to very few, or even one species of host. In open habitats, where the dominance of one or a few tree species is usual, natural selection favours close physiological adaptations in a mistletoe for growth on the predominant host species (Norton and Carpenter, 1998). In other words, the evolution of host specificity is largely correlated with the development of ecological dominance in plant communities (Barlow and Wiens, 1977).
Eucalypt on left, Mistletoe on right (Barlow, 2012)
Mistletoe on left, Eucalypt on right (Barlow, 2012)

                              
           It has been debated whether or not this phenomenon is true mimicry or just visual similarity, however, research has supported a firm genetic basis on which this mimicry could be founded. Analysis of the genetic variation within and between mistletoe races, compared to that occurring between mistletoe species, might indicate speciation that is host-specific (Norton and Carpenter, 1998). Phylogenetic comparison of mistletoes and their hosts would reveal the relative importance of co-speciation and host-switching events in mistletoe speciation (Norton and Carpenter, 1998). Further research is needed to be sure of this mimetic-genetic relation and its implications for parasite-host evolution and ecology.







References

Barlow B 2012, “Do mistletoes show cryptic mimicry of their hosts?”  Mistletoes in Australia, An Australian Government Initiative.
Barlow BA and Wiens D 1977, “Host-Parasite Resemblance in Australian Mistletoes: The Case for Cryptic Mimicry,” Evolution, vol. 31, no. 1, pp. 69-84.
Norton DA and Carpenter MA 1998, “Mistletoes as parasites: host specificity and speciation,” TREE, vol. 13, no. 3, pp. 101-105.

Saturday 18 April 2015

The Sarraceniaceae Family

Sarraceniaceae is a family of carnivorous pitcher plants native to North and South America. These low-growing perennial herbs are notable for their modified pitcher-like leaves, which serve as pitfall traps to ensnare and digest insects and other small prey. They derive their common name from their hollow tubular leaves, which can take the form of a trumpet, a pitcher, or an urn (Encyclopaedia Britannica, 2015).



The carnivorous pitcher plants of the Sarraceniaceae are generally thought to have developed deceptive mimetic systems, advertising visual and olfactory signals, which provide them with the ability to deceive insects by attracting them into traps (Joel, 1988). The leaves are adapted to function like flowers in attracting insects: they are flowerlike in their striking colour patterns and shapes, and, during their active period in the summer, they exude nectar containing fructose, which is highly attractive to some insects. These leaves passively capture prey that are lured to the leaf’s mouth by its glistening surfaces or unusual colouration and transparent patches. Besides having flower-like leaves, all members of Sarraceniaceae produce flowers that are showy and have an agreeable scent. If an insect or other organism falls into the pitcher, stiff downward-pointing hairs and slippery walls prevent it from crawling back out. Exhausted, the animal eventually drowns in the liquid at the bottom of the pitcher. Protein-digesting enzymes and bacteria break down the insect’s body, allowing nitrates and other useful nutrients to be absorbed by the plant to supplement the poor soil conditions of its environment. The nodding flowers are insect-pollinated and are usually borne on long stalks to keep the pollinators away from the deadly pitchers (Encyclopaedia Britannica, 2015). Thus, these flowers have developed a separate system for attracting pollinators and prey.





Little is known about the evolutionary experimentation that led to the development of these carnivorous tactics, but other families of carnivorous plants have developed similar strategies in response to similar soil conditions (Schwaegerle and Schaal,  1979). New phylogenetic analyses are beginning to reveal the evolutionary relationships and the amount of convergent evolution present in the carnivorous plants, but the amount of research done remains somewhat limited (Ellsion and Gotelli, 2001).







References

Ellison, EM and Gotelli, NJ, 2001, Evolutionary ecology of carnivorous plants, Trends in Ecology and Evolution, vol. 16, no. 11, pp. 623-629.
Encyclopaedia Britannica, 2015, Encyclopædia Britannica Online, Sarraceniaceae. Retrieved 19 April, 2015, from http://www.britannica.com/Sarraceniaceae
Joel, DM, 1988, Mimicry and mutualism in carnivorous pitcher plants (Sarraceniaceae, Nepenthaceae, Cephalotaceae, Bromeliaceae), Biological Journal of the Linnean Society, vol. 35, pp. 185-197.
Schwaegerle, KE and Schaal, BA, 1979, Genetic Variability and Founder Effect in the Pitcher Plant Sarracenia purpurea L., Evolution, vol. 33, no. 4, pp. 1210-1218.

Photo
Photo from Learn About Nature retrieved 19 April, 2015 from http://www.carnivorous--plants.com/pitcher-plant.html

Tuesday 14 April 2015

The Passiflora Genus


The Passiflora genus is comprised of about 400 species of tendril-bearing, herbaceous vines commonly called passion-flowers. Some are important as ornamentals; others are grown for their edible fruits (Encyclopaedia Britannica, 2015; Yockteng et al., 2011). Many species of passion-flower are of particular interest to scientists studying coevolution and parasite-host interactions (Williams and Gilbert, 1981). These interactions are particularly complex between certain passion-flower species and Heliconiine butterflies.

One example of a Heliconiine butterfly and a passion-flower.


It is suspected that Heliconiine butterflies have been coevolving with Passiflora for a long time (Gilbert, 1982). Heliconiine butterflies deposit their eggs only on Passiflora vines, where the eggs hatch into larvae that feed voraciously on the leaves of the vine. It’s known that Passiflora plants evolved chemical defences against herbivory by Heliconiine butterflies and other insect herbivores (Williams and Gilbert, 1981). While these defences are effective against its other herbivorous attackers, the Heliconiine butterflies have evolved the ability to circumvent these defenses. The remarkable thing is that some species of the vine now have features that appear to mimic the distinctive bright yellow eggs of the butterflies (Gilbert, 1982). Studies have shown that passion-flower plants that present bright yellow formations on the cuticle of the leaves are likely to deter actual oviposition by Heliconiine (Williams and Gilbert, 1981).


Egg mimic on passion-flower leaf.

It is believed that the morphological development of these yellow spots on the cuticle is the current and ongoing step in the coevolution between these two actors (Williams and Gilbert, 1981).The question of how any one trait of a plant could be causally attributed to natural selection imposed by one species or genus of insects among so many has been investigated in depth for the passion-flower-Heliconiine relationship. With only a few major herbivores such as Heliconiine to account for, interpreting the defensive traits of passion-flower vines is relatively free of ambiguity (Gilbert, 1982). Although not all species that interact with Heliconiine have developed this morphological trait, the hypothesis is that this trait will be developed in the near future, as this coevolutionary step is still in progress (Williams and Gilbert, 1981; Gilbert, 1982). For this reason, these relationships are of particular interest to ecologists and evolutionary biologists. In the far future, who knows how the Heliconiine butterflies will circumvent this new defensive tactic?











References

Encyclopaedia Britannica, 2015, passion-flower, Encyclopaedia Britannica. Retrieved on 14, April, 2015 from http://www.britannica.com/passion-flower
Gilbert, LE, 1982, The Coevolution of a Butterfly and a Vine, Scientific American, vol. 247, pp. 110-121. Retrieved 14, April, 2015 from http://imap.passionflow.co.uk/downloads/gilbert
William, KS and Gilbert, LE, 1981, Insects as Selective Agents on Plant Vegetative Morphology: Egg Mimicry Reduces Egg Laying by Butterflies, Science, vol. 212, no. 4493, pp. 467-469. Retrieved 14, April, 2015 from http://www.jstor.org/stable/1686077
Yockteng, R, d'Eeckenbrugge, GC, and Souza-Chies, TT, 2011, Wild Crop Relatives: Genomic and Breeding Resources, pp. 129-171. 

Photos

Helliconiine retrieved from Heliconius Butterfly Works.
Passiflora retrieved from Grassy Knoll Exotic Plants.
Egg Mimic photo by Lawrence Gilbert.

Tuesday 7 April 2015

The Lithops Genus


Many species of plants and animals have evolved striking visual resemblances to inanimate objects found in the same locality. Examples can be found in a diverse array of taxa (Skelhorn, Rowland, and Ruxton, 2010). For example, plants from the genus Lithops, also called living stone, flowering stone, or stoneface,  are named so because they visually resemble stones. These flowering stones can be any of a group of about 40 species of succulent plants of the carpetweed family and are native to southern Africa. The plants are virtually stemless, with two leaves growing during each rainy season forming a fleshy, roundish structure that is slit across the top (Encyclopaedia Britannica, 2015).

Structure of Lithops plant from "The Morphology of Lithops"


The succulent leaves are hypothesized to have three evolutionary purposes. First, because the leaves are sunken into the ground and lack the ability for stomatal transpiration, they are thought to serve as protection against evaporation (Eller and Ruess, 1982). The succulent leaves also effectively serve as a light transmitter to photosynthetic tissue below ground (Bennett et al., 1988). These adaptations have allowed the Lithops plants to thrive in very dry, arid environments and radiated and found small niches throughout southern Africa, promoting rapid speciation (Kellner et al., 2011). Lastly, but certainly not the least of all evolutionary adaptions, is the remarkable specialisation of vascular tissues to mimic local soil types. This adaptation has been found to create a camouflage for protection against herbivory (Kellner et al., 2011). It is quite amazing that Lithops can be found on every soil formation, ranging from granite to sandstone or limestone.


Collection of Lithops courtesy of Index of Aizoaceae


Little is known about the genetic relationships within the Lithops genus at present. As of now, its taxonomy is completely based on morphology. Kellner and his colleagues created one of the first phylogenetic trees in 2011, showing that the many species within Lithops are possibly a result of parapatric and allopatric speciation. More research is needed in order to determine the evolutionary relationships between the species in the Lithops genus, but it is clear that because of the large morphological variability due to geographic distribution, morphological trees are inaccurate. 












References

Bennett, B., Brito, C., Calvert, B., Cooper, J., Dennis, N., Holman, W., Patmore, J., and Stiver, J., 1988, British Cactus & Succulent Journal, 6 (2), pp. 44-45. Retrieved 07, April, 2015, from http://www.jstor.org/stable/42794129

Eller, B. M., and Ruess, B., 1982, Physiologia Plantarum, 55, pp. 329-334. Retrieved 07, April, 2015, from http://onlinelibrary.wiley.com/doi/10.1111/

Encyclopaedia Britannica, 2015, Encyclopaedia Britannica Online, lithops. Retrieved 07, April, 2105, from http://www.britannica.com/EBchecked/topic/343776/lithops

Kellner, A., Ritz, C. M., Schlittenhardt, P., and Hellwig, F. H., 1982, Plant Biology, 13, pp. 368-380. Retrieved 07, April, 2015, from http://onlinelibrary.wiley.com/doi/10.1111/

Skelhorn, J., Rowland, H. M., and Ruxton, G. D., 2010, Biological Journal of the Linnean Society, 99, pp. 1-8. Retrieved 07, April, 2015, from http://onlinelibrary.wiley.com/doi/10.1111/



Photos

Structure of Lithops retrieved 07, April, 2015 from http://www.floweringstones.co.za/morphology/morphology.html

Collection of Lithops retrieved 07, April, 2015 from http://www.flowershots.net/web-content/Aizoaceae/lithops2_.jpg

Saturday 28 March 2015

The Carrion Plants


“Sapromyiophilous” flowers – those which attract carrion and dung flies through mimicry of their food and brood sites – have evolved in many angiosperm families (Ollerton and Raguso, 2006). These species have foul-smelling flowers which are typically brown with purple or reddish blotches and often unusually large, as exemplified by Stapelia gigantea and Rafflesia arnoldii (Barkman et al., 2008).

Stapelia gigantea (left) by World of Succulents and Rafflessia arnoldii (right) by Marian Florcita.


There is now good evidence that the attraction of flies to these flowers depends heavily on the emission of volatiles that are used by flies as cues to locate carrion, faeces and even urine (Shuttleworth and Johnson, 2010). These chemicals emitted by the flowers have been found to structurally resemble those of carrion, and the pollinators could not physically distinguish the two smells (Stensmyr et al., 2002). Attraction of flies through mimicry of their food and brood sites is not confined to angiosperms. There is now good evidence that this occurs among both mosses and fungi, which provides an excellent basis for the study of convergent evolution (Fischer and Vicha, 2003.)
It has been hypothesized that the adaptation of these carrion scents arose from floral scent experimentation (Shuttleworth and Johnson, 2010). As the flowers cannot pick and choose what they mimic, this hypothesis makes sense. With the successful pollination by flies and beetles looking for carrion brooding sites, these chemical odours provided and evolutionary advantage, thus leading to a diverse range of carrion plants. Some of these plants even thermoregulate to further mimic carrion.


Amorphophallus titanum by Smithsonian.


Today there are over 75 identified species of carrion flowers (Stapelia) alone, only belonging to the milkweed family. With at least two other genera in the angiosperms, as well as the mosses and fungi, one can imagine the number of species that employ this mimicry tactic. It is important to remember, though, that although these species are very different, the chemical compounds used in this mimicry are similar or identical (Johnson and Jurgens, 2010). For this reason, these species are a fantastic example and basis for the study of convergent evolution. 









References

Barkman, T.J., Bendiksby, M., Lim, S.H., Salleh, K.M., Nais, J., Madulid, D., Schumacher, T., 2008. Accelerated rates of floral evolution at the upper size limit for flowers. Current Biology 18, 1508–1513.Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/18848446
Fischer, O.A., Vicha, R., 2003. Blowflies (Diptera, Calliphoridae) attracted by Phallus impudicus (Phallaceae) and Stapelia grandiflora (Asclepiadaceae). Biologia 58, 995–998. Retrieved from http://eurekamag.com/research/004/059/004059130.php
Johnson, S. D., Jurgens, A., 2010. Convergent evolution of carrion and faecal scent mimicry in fly-pollinated angiosperm flowers and a stinkhorn fungus. South African Journal of Botany 76, 796-807. Retreived from http://www.sciencedirect.com/science/article/pii/S0254629910001894
Ollerton, J., Raguso, R.A., 2006. The sweet stench of decay. The New Phytologist 172, 382–385. Retrieved from http://onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.2006.01903.x/full
Shuttleworth, A., Johnson, S.D., 2010. The missing stink: sulphur compounds can mediate a shift between fly and wasp pollination systems. Proceedings of the Royal Society B-Biological Sciences 277, 2811–2819. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2981988/
Stensmyr, M.C., Urru, I., Collu, I., Celander, M., Hansson, B.S., Angioy, A.M., 2002. Rotting smell of dead-horse arum florets. Nature 420, 625–626. Retrieved from http://www.nature.com/nature/journal/v420/n6916/abs/420625a.html

Photos

Stapelia gigantea by World of Succulents. http://www.worldofsucculents.com/stapelia
Rafflessia arnoldii by Marian Florcita. https://www.flickr.com/photos/marucs/galleries/
Amorphophallus titanum by Smithsonian. http://botany.si.edu/events/amorphophallus/







Saturday 21 March 2015

The Ophrys Genus


           The Ophrys genus belongs to the Orchidaceae family and contains approximately 30 species. These species are native to Eurasia and North Africa. All have metallic-coloured, hairy flowers that resemble insects (Ophrys 2015). Male insects are lured to the orchid by visual cues and chemical signals. At close range, these signals elicit sexual behaviour in males, whereby the males try to copulate with the flower (Ayasse, et al., 2000). During this process, commonly called pseudocopulation, pollen sacs become attached to the insect’s body and are transferred to the next flowers visited. The fly orchid (O. insectifera) and the bee orchid (O. apifera) are common European species (Ophrys 2015).





Ophrys species are interfertile, meaning they are capable of interbreeding. It is because of this interfertility that reproductive isolation among taxa heavily depends on specific pollinator interaction. Floral odour differences between plant species have often been interpreted as an adaptation to the attraction of distinct pollinators (Dodson et al. 1969). For Ophrys species that are often strongly pollinator limited, selection pressures are imposed by pollinators with different sex pheromone preferences (Ayasse et al. 2000). This pressure is thought to drive floral odour differentiation among orchid populations, ultimately generating adaptive change and species divergence through pollinator shifts (Schiestl and Ayasse 2002).
This genus is a spectacular example of deception and Batesian mimicry in plants. Due to the Ophrys species’ high dependence on specific pollinator interactions, a commensalistic relationship has developed. I can imagine in 50 years the pollinators will have developed a way to identify this deception, however, in the far future it is sure to become a fantastic example of coevolution.






 References

Ayasse, M. et al., 2000. Evolution Of Reproductive Strategies in the Sexually Deceptive Orchid Ophrys sphegodes: How Does Flower-specific Variation of Odor Signals Influence Reproductive Success?. Evolution, 54(6), pp. 1995-2006.http://www.bioone.org/doi/pdf/10.1554/0014-3820%282000%29054%5B1995%3AEORSIT%5D2.0.CO%3B2
Ophrys. 2015. Encyclopædia Britannica Online. Retrieved 22 March, 2015, from http://www.britannica.com/EBchecked/topic/430060/Ophrys
Schiestl, F. P., and M. Ayasse. 2002. Do changes in floral odorcause speciation in sexually deceptive orchids? Plant Sys. Evol.234:111–119. http://www.researchgate.net/publication/225554285_Do_changes_in_floral_odor_cause_speciation_in_sexually_deceptive_orchids


Thursday 5 March 2015

The Plant Kingdom





The plant kingdom, Plantae, is comprised of all land plants and developed between 488.3 million years ago and 443.7 million years ago. It is between these dates that the fossil record contains the miniscule remnants of the first organisms to colonize land (Speer, 1997). In the enormous span of time between then and now, one can imagine the evolutionary experimentation that has taken place. With more than 300,000 known species in the plant kingdom, there is immense competition for nutrients, water, reproductive success, and space (Dickison, 2015). Many species have developed very complex and unique adaptations for dealing with competition. Some of the most interesting are plants that use deception and mimicry to acquire nutrients, attract pollinators, and defend against herbivory.
Before delving into these amazing plants and their unique adaptations, we must distinguish between deception and mimicry as these terms imply different qualities. Deception is often used in the plant kingdom to trick other organisms into providing a service beneficial for the plant (Dafni, 1984). C. K. Sprengel, founder of modern floral biology, recorded in the late 1700s the many deceptive tactics of the genus Orchis, which contains approximately 125 species of orchids. He studied these flowers and found that by appearing similar to a nectar-producing flower or other organism, these plants could attract pollinators and spread pollen without spending energy and resources on actually producing nectar (Dafni, 1984).

Ophrys eleonorae and Ophrys lupercalis, a wild hybrid orchid, whose pollinator, a male solitary bee, is engaged here in pseudocopulation (Pollan, 2011). Photograph: Christian Ziegler/Minden Pictures


          Mimicry is somewhat more complex and can be one of two types. Müllerian mimicry has been defined as when multiple species develop similar traits providing both with an advantage (Barrett, 1987). An example of Müllerian mimicry can be seen between Lantana and Asclepias. Batesian mimicry has been defined as mimicry of one organism or object by another allowing a one-sided advantage to that organism. An example of Batesian mimicry can be found in the genus Lithops (Barrett, 1987).


Mullerian mimicry between Lantana (left) and Asclepias (right). Photographs:Mercewiki (left) and B.T. Wursten (right)


Lithops plants resembling rocks: and example of Batesian mimicry. Photograph: Dysmorodrepanis


            Both deception and mimicry are used in many families and genera of plants around the world. Over the next 11 weeks, I will discuss different techniques of mimicry and deception, how they developed, and the evolutionary advantages these adaptations provide for the taxa they belong to. 










References
Barrett, S. C. H., 1987. Mimicry in Plants. Scientific American, September.255(9).
Dafni, A., 1984. Mimicry and Deception in Pollination. Annual Review of Ecology and Systematics, Volume 15, pp. 259-278.
Dickison, W. C., 2015. Plant, s.l.: Encyclopedia Britannica Online.
Pollan, M., 2011. The weird sex life of orchids. Available at: http://www.theguardian.com/science/2011/oct/09/orchid-sex-botany-ziegler-pollan [Accessed 5 March 2015].
Speer, B. R., 1997. Introduction to the Plantae, Berkeley: University of California Museum of Paleontology.