Dr. Moalem refers to multiple experiments that include parasites Hymenoepimecis argyraphaga (parasitic wasp), Dicrocoelium Dentriticum (lancet liver fluke), and Spinochordodes tellini (parastic hairworm). According to the observations in the conducted experiments, these parasites live and grow on a host until they seemingly control the behaviors of their hosts for their own benefit. Refer to pages (100-105). This relates to Big Idea 1: the process of evolution drives the diversity and unity of life.
Define host manipulation and how it favors parasitic organisms to achieve their goal in life (what drives evolution?). Using one of the parasitic organisms on pages (100-105), describe how that organism came to be to able to manipulate a host for its own benefit. Refer to past information from Unit 1 (Evolution) and the evolutionary flow chart. Since parasitic organisms live and kill their hosts in order to survive and reproduce, how is that the entire species of the host organism isn't killed off. By referring to information from Unit 1(Evolution), specifics about natural selection, and the evolutionary flow chart, explain how the species of host organisms are not completely killed off by parasites. Finally, Dr. Moalem refers to a parasite, Toxoplasma Gondii, and the increasing evidence that it can effect human behavior such as schizophrenia. Explain how the human race is able to survive and reproduce despite a parasites similar want to survive and reproduce. To test your understanding, research another parasite not used in the book and explain how it effects human behavior. Using information from Unit 1 (Evolution), explain how humans are able to adapt, survive, and reproduce given that the parasite wants to do the same.
Posted by Weilly Tong (wtong4@students.d125.org)
Posted by Weilly Tong (wtong4@students.d125.org)
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ReplyDeleteHost manipulation is the phenomenon that occurs when a parasite is able to manipulate its host into helping it achieve its main goal in life, which is to survive and reproduce. This connects with the BIG Idea 1, which states, "The process of evolution drives the diversity and unity of life". This is because of the way that parasites have evolved to be able to take control of other organisms for their own benefit.
ReplyDeleteOne species relationship that Dr. Moalem talks about is the relationship between Plesiometa Argyra, a web weaving spider, and Hymenoepimecis argyraphaga, a parasitic wasp. The way that the wasp takes over the spider is mapped out by Dr. Moalem.
First, the wasp stings the spider to paralyze it, then lays an egg on the spider's abdomen. This egg soon hatches into a larva. However, the spider is still spinning webs and going about its own business. The larva lives off the spider's blood, then injects chemicals into the spider. These chemicals change the spider's behavior, making it spin webs in a way that will help only the cocoon of the larva. It is not yet understood how the chemicals do this, but we are certain it is due to the released chemicals. This is because when experimental removals of the wasp were performed, the spider still continued to spin it web in heavy radial lines. But these actions are performed during a specific section of weaving a normal web. Thus, it seems that the wasp is able to initiate very specific responses out of the spider. http://www.americanarachnology.org/JoA_free/JoA_v29_n3/arac_29_03_354.pdf
This makes the spider only care about the survival and reproduction of the wasp, not itself, which is a change from the biological principle that drives evolution. This is why the ability to manipulate hosts is so strange and unique. It is literally changing the way that species function and makes them essentially give up themselves.
Toxoplasma Gondii is a parasite that survives in any mammal but can only reproduce in cats. The parasite reproduces by infecting epithelial cells of the cat. It is here where they reproduce, making zygote containing cysts, known as oocysts. These cells rupture and release the oocysts, which will eventually leave the body in the feces. From here, the oocysts can contaminate soil, water, and food. They can then move from the infected environmental agent and then infect other mammals. The cyst walls are destroyed by enzymes in the digestive system and this allows for the parasites to infect host cells. However, because they cannot sexually reproduce, this host is only called an intermediate host.
The reason that humans are able to survive with this parasite is due to the fact that it cannot reproduce inside humans, instead making it much worse for cats. But humans with weakened immune systems are at risk and must be careful to not get infected. However, if The phenomenon of host manipulation by parasites has much left to uncover.
Sources: http://www.stri.si.edu/sites/publications/PDFs/2000_J_Hym_Res_The_natural_history_and_behavior_Hymenoepimecis_argyraphaga.pdf http://www.bioone.org/doi/abs/10.1636/0161-8202%282001%29029%5B0354%3AUTIWAB%5D2.0.CO%3B2?journalCode=arac
http://www.ncbi.nlm.nih.gov/pubmed/21539466
Patrick Austin (paustin4@students.d125.org)
Parasitism in general, is a non-mutual relationship in which a parasite organism benefits at the expense of a host. Host manipulation is when a parasitic organism is able to take over part of a host organism's behavior and manipulate the host into facilitating the parasite's ability to survive and reproduce. The fact that the parasite influences the function of a host is the unique part about this type of parasite because it is not known entirely what causes the host to go completely against the usual selfishness involved in survival and reproduction to do something that has no benefit to itself. This connects to big idea 1, the process of evolution drives the diversity and unity of life, because these parasites have been naturally selected for the optimal variation to manipulate the host.
ReplyDeleteT. gondii is a type of host manipulating parasite that can infect most animals, but can only survive and reproduce in cats. Infected cat cells produce spore cells called oocysts of the parasite that are distributed in the cat's droppings. Animals and humans can be infected by ingesting the oocysts either directly or eating infected flesh. The T. gondii cells are distributed into the muscles and brain cells. While T. gondii is mostly harmless in most organisms, it is especially vicious in mice and rats. According to Dr. Moalem, "Once inside the mouse's brain, in ways that are not completely understood, the parasite has a profound effect on its behavior. First, the mouse becomes fat and lethargic. Then, it loses its natural fear of predators- of cats. In fact, some studies have shown that instead of fleeing areas marked with cat urine, infected mice are actually drawn by its scent" (106-107). Basically T. gondii manipulates the mouse to get eaten by cats so that it can infect the cat and survive and reproduce. This likely occurred because the T. gondii that were able to change the behavior of rats even slightly were more likely to survive and reproduce, so over time the variation of T. gondii that were able to manipulate rats become naturally selected, leading to the evolution of host manipulating T. gondii.
T. gondii also can affect humans, causing humans to be more likely to get schizophrenia. This isn't host manipulation though because it doesn't help the parasite because they can't survive and reproduce in humans. The manipulation designed for the rodents also, coincidentally, has an effect on humans, which is why humans react to being infected. Also, like Patrick said, "The reason that humans are able to survive with this parasite is due to the fact that it cannot reproduce inside humans, instead making it much worse for cats. But humans with weakened immune systems are at risk and must be careful to not get infected. However, The phenomenon of host manipulation by parasites has much left to uncover."
Even though hosts are not benefitted at all from these host parasites, and are often killed, there is good reason why the host population doesn't all die out. The reason is that the parasites are dependent on the hosts. If all the hosts died, the parasite would have no method of surviving and reproducing, so the parasite would also die off.
Tony Massat amassat4@students.d125.org
Besides for T. gondii, other organisms also establish a host manipulation lifestyle. Jewel wasps are able to manipulate cockroaches to burrow into a hole and then injects the cockroach with its egg. According to Frederic Libersat, "parasitic jewel wasps rob cockroaches of their capacity for independent movement. Inflicting non-lethal injections to initially paralyse and then incapacitate the cockroach’s ability to move of its own free will, the wasp then leads the docile victim to a burrow where it is entombed with a single egg, and subsequently consumed by the developing larva and pupa" (http://jeb.biologists.org/content/216/1/i.full.html?etoc%3Ehttp://jeb.biologists.org/content/216/1/i.full.html?etoc). By affecting the cockroaches motor neurons and reducing the cockroaches drive to move on its own, the wasp is able to manipulate the cockroach to help itself survive and reproduce.
ReplyDeleteTony Massat amassat4@students.d125.org