Carnival transformations in the natural world
At Carnival time, humans like to think that we can be masters of disguise and transformation: men dressed like women; and women like jamettes, or birds… But throughout the world there are plants and animals disguising and transforming to ensure their survival. What would an acacia tree do to prevent its leaves from being eaten? Or an insect living near flowers to get more food? Dr Anjani Ganase looks at some specific animals and plants
Plants that behave like Animals
Ti- Marie (Mary, Mary Shut your door or Touch Me Not!), also known as Mimosa pudica was always a memorable childhood introduction into more interesting plant life, precisely because it responded like an animal when touched. This reaction is an evolutionary strategy where the plant is able to retract its leaflets upon being touched. This response to touch is known as thigmotaxis. The mechanism of the folding results from a change in the turgidity in the “hinge” where the leaflets are attached to the main stem. The touch results in the shift in potassium and chloride ions from one part of the hinge to the other. This results in the leaflets closing in and revealing the spines along the stem. Even though plants don’t have a brain and touch response is automatic, scientists do notice behavioural change where the speed of response is often correlated to the intensity of the touch, where a firm brush of the leaves will cause a rapid shutting of the leaflets along the stem, while a gentle touch will result in a slower reaction. They also noticed that older leaflets tend to fold only partially, likely because they are the less preferred meal than the younger parts of the plant.
Pisonia trees are common in the Indo-Pacific region but more recently discovered in the forests of Puerto Rico. This tree is also known as the bird catcher because of its disturbing relationship with birds. These trees can be found on small islets that also serve as nesting colonies to birds. The trees benefit from these nesting birds, typically noddies, boobies and shearwaters, by having their fruits latch on to the feathers of the birds with hooks and sticky sap along the seed to be carried off to distant islands for colonisation. However, at times the evolutionary relationship can take a sinister turn. Sometimes young fledglings, while learning to fly, may get one too many sticky barbs attached to their bodies, and as they cannot fly or feed or even move, they eventually starve and die. It was thought that the Pisonia may benefit from the nutrients from the dead bird’s carcass, but they actually benefit more from having the birds alive: both for the guano that supplies nutrients and to carry the seeds away.
Acacia trees are a common source of food for a number of grazing animals, such as antelopes and giraffes in Africa. However, during times of stressful environmental conditions, such as severe episodes of droughts, scientists have observed that the plants tend to focus their resources on defence mechanisms to deter grazers from foraging too much and removing too many of their leaves. Part of the defence results in the reduction of the growth of the plant’s leaves and an increase in the concentrations of the tannins that make the leaves less tasty, as well as an increase in toxins in the leaves.
What’s more curious is the communicative alarm system set up among the plant species, where they release the chemical ethylene into the atmosphere to notify neighbouring acacia plants within fifty yards of the grazing threat, so that they can beef up their defence systems as well. This strategy was discovered by scientist Van Hoven who was hired to investigate the death of 3000 antelopes during the drought that resulted from the concentration of tannins becoming lethal in such high concentrations. When conditions become more favourable, and tree growth returns to normal, the plants again return to their normal conditions and reduce toxin concentrations.
Animals that behave like Plants
Corals are marine animals that many mistake for colourful rocks underwater because they grow and settle in one spot for the rest of their lives, similar to trees. Corals also grow with the assistance of sunlight from tiny individual polyps; they can become large rock structures that can be seen from space. Corals have a special symbiotic relationship with single celled algae called dinoflagellates. These algae live within the tissues of the coral and carry out photosynthesis to convert sunlight into food. The algae share excess nutrients with the coral animal and in return the coral provides the algae with essential ions and removes their waste. The relationship is so efficient that the coral is able to grow through the process of calcification where they create a calcium carbonate rock skeleton and the rocky skeleton is responsible for providing homes to thousands of marine organisms on coral reefs.
Stick insects have evolved to be masters of disguise by resembling sticks to protect themselves from predation from birds and mammals. This evolution was thought to come around just after the age of dinosaurs, when there was the rise in birds and mammals as well as the explosion of the species of flowering plants to replace the evergreens that previously dominated the landscape. As a result, there was a co-evolution of stick insects to mimic the branches of these plants to escape predation with considerable success.
The female orchid mantis, unlike the stick insect, has evolved to mimic ornate orchids to capture pollinators as prey. As the mantis began hanging around the orchid flowers to capture prey, over a long time they started to resemble the ornate flowers that allow the camouflaging of the mantis and luring of unsuspecting pollinators. Interestingly, the male mantis remained small and better camouflaged with the foliage because they were more at risk of becoming prey when moving around to seek out mates. Females, on the other hand, hung around the orchids for their meals. The orchid mantis females are large with white, yellow and pink colours and typically found in the Indo-Pacific.
Throughout the plant and animal kingdoms, there are species with “crossover” characteristics that allow them to survive in their ecosystems. Let us celebrate the masquerade of nature.
References
Alan E. Burger, Dispersal and Germination of Seeds of Pisonia grandis, an Indo-Pacific Tropical Tree, Journal of Tropical Ecology, Vol. 21, No. 3 (May, 2005), pp. 263-271
Cambridge University Press
Benjamin Blonder, Dana L. Royer, Kirk R. Johnson, Ian Miller, Brian J. Enquist. Plant Ecological Strategies Shift Across the Cretaceous–Paleogene Boundary. PLoS Biology, 2014; 12 (9): e1001949 DOI: 10.1371/journal.pbio.1001949
Patil H. S., Vaijaparker S. Study of the Geometry and Folding Pattern of Leaves of Mimosa pudica Journal of Bionic EngineeringApril 15, 2007
Svenson, Gavin J., et al. "Selection for predation, not female fecundity, explains sexual size dimorphism in the orchid mantises." Scientific Reports 6.1 (2016): 1-9.
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