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