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Introduction:

Symbiotic relationships are not uncommon in the world around us, the tropics being no different. Most fauna and flora will exhibit some level of symbiosis with another organism throughout its lifespan in one form or another. To understand what makes an organism symbiotic, one will first have to understand what the word means. Symbiosis literally means “living together” and so this is when two organisms, unlike in nature, live together!1!. This simple definition can be broken down more depending on how the two relate and benefit from each other. If one participant benefits while the other is neither harmed nor helped by the relationship, it is said to be commensalistic. If both parties receive positive rewards from their symbiosis, it’s referred to as being mutualistic. Another form is parasitism, which is when one benefits (the parasite) at a harmful and injurious cost to the host. To better understand how these relationships work, examples will better explain.

In the forests of northeast South America, there is a furry long armed mammal that inhabits the high canopy regions called the three-toed (Bradypus sp.) or the two-toed sloth (Choloepus sp.). The sloths are interesting creatures indeed because they are in fact their own mini-ecosystem!2!. Due to their slow pace lifestyle, the bodies of these sloths are home to many invertebrates, including those which can only be found on sloths, Bradypus sp. being more common homes. One group of these hitchhikers are called sloth moths. They live in the relative safety in the hair of the high canopy sloths away from avian predators. These mammals that only come down to the ground floor to defecate about once a week, and when they do, the moths depart laying their eggs into the fresh dung. The larvae then eat from the nutritious pellets until they grow up and live on another moth themselves. This relationship between the sloth and the moth is an example of commensalism because the moth benefits while the sloth is unaffected.
Sloth with moth along its back
Sloth with moth along its back
Another example on a commensalistic relationship would be that of the many epiphytes, such as the bromeliad, growing in the trees. Epiphytes are plants that do not grow how we imagine a normal plant growing. They grow mostly on the sides of larger tree trunks!3!. They are able to acquire their nutrients in the air around them, as opposed to the roots which we imagine to be normal. Most of the time, they do not hurt the host tree and only use them as a platform to live off of. Since the epiphyte doesn’t harm the host tree, it’s easy to see how this relationship would be commensalistic.
Bromeliad, a type of epiphyte, growing on the side of a tree in Brazil.
Bromeliad, a type of epiphyte, growing on the side of a tree in Brazil.
Next, we talked about mutualism. For this, we should go back to the three-toed sloths we spoke about before. These sloths, as previously mentioned, are sloth high-canopy creatures which are little mini-ecosystems. Their long outer hair is hollow, making them the perfect home to green algae!4!. This algae gets a safe easy home high in the trees where as the sloth gets a little extra green discoloration camouflage to help avoid predators. Both organisms are mutually benefiting from the relationship.
Three Toed Sloth Green.jpg
Three-toed Sloth with her young showing the difference of coloration with green algae growth
Bromeliads are epiphytes which are living in a commensalistic relationship on other trees. These bromeliads are often filled with water because of the amount of rainfall in the tropical rainforests. Every animal needs a steady source of water, and the treefrogs (one being the Scinax hayii) use these pool catches as their homes for most of their life. When a bromeliad has a frog guest, they receive more nutrients from the frog’s food and from its droppings!5!.
Frog living in a Bromeliad.
Frog living in a Bromeliad.
Lastly, parasitism is when an organism hurts that of another while reaping all of the benefits. This is the one which society seems to be most knowledge about because of the possible diseases these vectors can carry. Mosquitoes and ticks are two possibly deadly animals that live on their host taking nutrients through the host’s blood!6!!7!. Whereas all ticks feed on blood, only the female mosquitoes do because the males drink plant nectar. Ticks and female mosquitoes are called ectoparasites because they live on the outside of their hosts for a short time needing blood. The host doesn’t receive anything beneficial and gets an irritating bug bite which could become infected and contract many diseases.
mostick.jpg
(Left) Mosquito. (Right) Tick.
A really interesting parasite of the tropics is the Myrmeconema neotropicum. This endoparasite, a parasite that lives inside its host, has been found to live inside the ant species, Cephalotes atratus. The ants live relatively normal lives foraging for food around their nests. They are black in color and are found climbing trees of the rainforests for food. When they retrieve nutrients from an infected bird’s droppings, they pick up the parasite eggs!8!. The larva matures inside the gaster of the ant where the male and female mate before the male dies off. This process causes a morphological change in the gaster of the black ant as it turns it as red as the berries in the trees nearby. It also causes behavioral changes making the ant venture off more than normal and walks around with its gaster in the air. This abnormal behavior gets it eaten by birds, which the eggs get passed back through the feces.
C_atra_2.JPG
Cephalotes atratus without parasite (Steve Yanoviak/University of Arkansas)
IMG_5677.jpg
Cephalotes atratus near berries to show mimicry. (Steve Yanoviak/University of Arkansas)

Conclusion:

IMG_5630.jpg
Cephalotes atratus with parasite (Steve Yanoviak/University of Arkansas)
There are many more animals that find themselves in some sort of symbiotic relationships including us and the gut bacteria in our own intestines. Evolution has shown the advantage of working with another species to better increase one’s own survival rate. Evolutionarily making, or taking, food, shelter, safety, water collection, nutrients easier to collect is a huge benefit of adapting to a life style with that of another organism. Our ecosystem is a delicate and extremely intricate web that needs to be balanced. It's been hypothesized, but not proven, that the extinction of the dodo bird helped lead to the near extinction of the dodo tree!9!. Botanists use turkey's now, which are similar to the dodo, to help break down the seeds for germination. Either way, we can never truly know what we are losing when an animal or plant goes extinct and if we do find out, it's already too late. Organisms have evolved to depend on each other for help to survival and let's do our part to ensure that happens. We can all experience mutualism with our environment.




References:
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  2. Hayssen, V. (2009). Bradypus tridactylus (Pilosa: Bradypodidae). Mammalian Species, (839), 1-9. doi:10.1644/839.1
  3. Lynch, Meghan. "What Is An Epiphyte?." Horticulture 104.7 (2007): 51-52. Academic Search Premier. Web. 22 July 2012.
  4. Jaanika Blomster, et al. "Molecular Evidence For A Diverse Green Algalcommunity Growing In The Hair Of Sloths And Aspecific Association With Trichophilus Welckeri(Chlorophyta, Ulvophyceae)." BMC Evolutionary Biology 10. (2010): 86-97. Academic Search Premier. Web. 22 July 2012.
  5. Denise De C. Rossa-Feres, et al. "Nitrogen Fluxes From Treefrogs To Tank Epiphytic Bromeliads: An Isotopic And Physiological Approach." Oecologia 162.4 (2010): 941-949. Academic Search Premier. Web. 22 July 2012.
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  7. "A Malaria Transmission-Directed Model Of Mosquito Life Cycle And Ecology." Malaria Journal 10.1 (2011): 303-319. Academic Search Premier. Web. 22 July 2012.
  8. Sanders, Robert. "Ant Parasite Turns Host into Ripe Red Berry, Biologists Discover." UCBerkeley News. Http://www.berkeley.edu, 16 Jan. 2008. Web. 22 July 2012. <http://www.berkeley.edu/news/media/releases/2008/01/16_ants.shtml>.
  9. "Dodo tree." Dave's Garden. davesgarden.com. 25 July 2012. http://davesgarden.com/guides/pf/go/153665/
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1. Yanoviak, S. (Photographer). [Ant in berries]. Retrieved 21 July 2012, from: https://dl.dropbox.com/u/29312442/IMG_5677.jpg