Parasites: Pilferer or Peacemaker

As I stand here just off of Riverside drive gazing across the Tony Tank inlet on a clear and cool autumn afternoon, my feet find themselves sinking into the mud normally underlying tidal waters. A couple hours before or after this moment I may have found myself submerged shin-deep in Maryland’s Wicomico River. But for now the tide has gone out and my kneecaps remain dry.  Around me lies much more than the leafless branches of the eastern shore’s deciduous trees, and the desolate forest floor which looks barren of all but its disintegrating leaf litter. Beneath my sole-sunken heels reside the herbaceous perennial tubers of a hibernating Sagittaria latifolia Willd; or better known as the Broadleaf Arrowhead.

Natural history occurs when you go into the field, and the field not only answers the questions you have brought with you but also asks a few of its own. I never knew exactly what natural history meant before this class. I had only visited the Natural History Museum in DC and that was to see the Hope Diamond. For my project I ultimately decided to study the parasitic relationship between Broadleaf Arrowhead and Dodder. A parasitic relationship is one between two species of plant or animal where one benefits at the expense of the other. In this case the Arrowhead was the host species for the parasitic Dodder. In order to fully understand the relationship between the Broadleaf Arrowhead and the Dodder I had to completely immerse myself into their environment and observe the two participants in the most attentive way possible. Doing so was not easy and took a lot of time and patience. Through my observations and natural history research I found their relationship to be more intricate than the archetypal one of predator versus prey.

My observations took place only a few minutes from Salisbury University across from the Tonytank pond. At first my observations were superficial and not so attentive. I couldn’t seem to see the difference between my observations, and running through the woods and creeks as a kid, climbing old hunter’s posts and waiting for deer to pass by. After a while of observing what most people would take to be the same, unremarkable water day after day under the old bridge, I started to take a closer look. It wasn’t until around my fourth week of observations when I first noticed the bright green foliage of Broadleaf Arrowhead. I was struck by its pointed leaves with two flailing backsides that seemed to hang a little lower causing its tip to poke out into the sky. After further observations I began to conduct some research on the species. This interest sparked more awareness and curiosity about other strange and unidentified species which led to my discovery of the Dodder and the symbiotic relationship between them that I had become so fond of.

The emergent Broadleaf Arrowhead thrives in the freshwater wetlands between New Brunswick and British Columbia, and expands south as far as Florida, California and Mexico. It requires full sun exposure and can withstand 6 to 12 inches of water with a pH ranging from 6.0 to 6.5, but is tolerant of less adequate conditions. The Arum may only grow to be a scrawny 4 feet on average, but don’t be swindled by its physiognomy. The Broadleaf Arrowheads have a remarkable aptitude to extract extraordinary amounts of nutrients and metals from their surroundings due to highly rhizomatous capabilities. Although the herbaceous perennials reach their zenith in July, they continue to burgeon until mid-fall when they annually die back to their root crown. During their dieback, nutrients and carbohydrates are translocated to their subterranean tubers where they are able to dodge the callousness of winter, or even the malicious appetite of a parasitic Dodder.

Cuscuta L; otherwise known as Dodder, is a twining parasitic plant that is vastly interwoven throughout the temperate and tropical regions of the entire world. A Dodder seedling has, on average, a mere 10 days to seek out a suitable host before it perishes. Once the cunning Cuscuta ascertains a host and inaugurates itself, its roots audaciously rot away from the earth. The Dodder is not to be mistaken for your typical liana; a mature plant can live an entire life without attachment to the ground. The consistently counter clockwise spiral branching stems of the dodder range from thread-like filaments to heavy cords. This leafless creeper has a yellowish orange appearance due to the fact that it contains no chlorophyll, and is consequently dependent upon a host for its photosynthetic properties. Only through the Dodder’s haustoria does it procure nutrients. Haustoria are the microscopic arms of the Dodder that meticulously reach into the vascular system of the host plant and enthrall water and sugars.

Initially I thought the Dodder was colonizing the Arrowhead, against which the latter seemed defenseless. I had watched week after week as the Dodder creeped up the sturdy stalks of the arum until it reached its neck. By this point the arrowhead’s broad leaves had begun to change color and lose their vibrant green pigment, as if the plant’s blood flow was being choked out by the Dodder. I helplessly stood by as I watched the Arrowhead’s stems continue to teeter until they finally succumbed to the Cuscuta’s clench. I found myself unexpectedly distraught from what I was seeing, as I became increasingly fascinated with these plants and their intertwined fates. Need the arrowhead die simply because the dodder must feed?  But then I realized that the Dodder was also, almost simultaneously, losing its vivaciousness as the arrowhead succumbed. I realized the arrowhead was never completely threatened, that even though it was involved in a parasitic relationship, checks and balance were in place that functioned for the betterment of the entire tidal water ecosystem.

When most humans think of a parasite, the first thing that usually comes to mind is a dreadful bloodsucking organism that is pictured anthropomorphically as egotistical and unremorseful. It’s exceptionally typical for people to be biophobic of parasites and perceive them simply as the enemy; in doing so we form metaphors for our own social relationships with others that picture the parasite in a deleterious manner. Yet to do so is to hate nature itself.  Surprisingly, parasites make up over half of the worlds organisms, and every living thing on this planet has at least one parasite that lives on or even inside of it. While this thought likely makes most humans cringe, perhaps that reaction should be balanced with admiration for how parasites are responsible for the world’s biodiversity among species, and have even facilitated evolutionary change. Most parasites are not as narcissistic as people make them out to be. They can be as common and innocuous as the bacteria that you find on your own hands and hair. In fact, your body may be at even more risk of environmental harm without the presence of some bacteria and viruses, just like an ecosystem is in the absence of parasites. Their presence can actually be as indispensable as a keystone species at the top of a food chain.

Through my natural history observations and research I have come to the conclusion that parasites hold the same civic responsibility towards their ecosystem as humans do today, and should receive the same appreciation as keystone species do. Just like humans and the biotic upkeep we hold towards the environment we depend upon, parasites have a similar obligation in promoting biodiversity. Although parasites are generally considered to be harmful and many feel biophobic towards them, like keystone species, the eradication of all parasites would not necessarily be beneficial.  Parasites have been thought to be a dominant force, if not the dominant force, in the evolution of life; reducing the dominance of superior competitors and allowing competing species to co-exist. Parasites presence plays an important role in the vitality of our global ecosystems and ought to have the respect they deserve and be regarded not as pilferers, but peacekeepers.

Works Cited

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2.     Davidson, Tish; Frey, Rebecca. "Cuscuta." Gale Encyclopedia of Alternative Medicine. 2005. Encyclopedia.com. 14 Dec. 2015 <http://www.encyclopedia.com>.

3.     "Dodder". Encyclopædia Britannica. Encyclopædia Britannica Online.
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<http://www.britannica.com/plant/dodder>.

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5.     U.S. Department of Agriculture. Natural Resource Conservation Service. DUCK POTATO: Sagittaria Latifolia Willd. Natural Resources Conservation Service, 5 Feb. 2002. Web. 10 Dec. 2015. <http://plants.usda.gov/factsheet/pdf/fs_sala2.pdf>.

6.     Zimmer, Carl. "Do Parasites Rule the World?" Discover. Kalmbach Publishing Co., 1 Aug. 2000. Web. 10 Dec. 2015. <http://discovermagazine.com.proxy-su.researchport.umd.edu/2000/aug/cover>.