Crawling Chaos
BY ALPER ÖZKAN (MSN/PhD I)
Parasites are perhaps the most successful and definitely the most enviable forms of life. Many are so well-adjusted to their unique environment that it is well-nigh impossible to determine what their ancestors used to be prior to developing the myriad adaptations they now possess, leaving even molecular phylogenetics puzzled at times. The ways by which they enter their hosts and seize a niche for themselves are nothing less than ingenious, for countless dangers lurk within the confines of the host's body: parasites must first find a method to get themselves into their hosts and then endure digestive fluids and elude the immune defenses of their potential targets, recognize the location in which they may develop, fight with any number of other parasitic species for limited space and nutrients, learn to survive in environments almost completely devoid of oxygen and pull off many other feats impossible for any other creature. Yet while the dangers are great, so are the rewards. Only a few adult parasites among the thousands of eggs shed successfully establish themselves in a host, but those that do so obtain a lifetime of prosperity, and it should come as no surprise that parasites have crawled their way into virtually every environment containing potential hosts.
Naturally, the topic of this week's column will be parasites. By now I'm sure everyone has stopped reading, but if you've managed to get this far, fret not, because I won't mention any of the more disgusting ones that infest humans. Maybe.
I have discussed mind-controlling parasites before: larvae of the parasitoid wasp Hymenoepimecis argyraphaga are known to manipulate their host (a spider, in this case) to weave a modified web designed to protect them from the rain while they metamorphose. Such changes in behavior are by no means limited to the ones initiated by this wasp, however, and may affect far more complex animals. Toxoplasma gondii, a protozoan parasite of cats, utilizes rodents as an intermediate host and establishes itself in areas of the rodent brain associated with fear -- fear of cats, to be specific. The now cat-loving vermin are drawn to their predator and are promptly eaten, allowing Toxoplasma access to its final host. Of greater concern than its rat-puppeteering skill is the potential ability of Toxoplasma to induce changes in human hosts. While no comprehensive study has been done on the effects of the parasite, lower reaction times and increases in traffic accident risk were observed in Toxoplasma-infected men; curiously, heightened intelligence is another possible consequence of infection.
Other parasites manipulate their hosts in far more insidious ways. Gordion worms force grasshoppers to drown themselves so that the adult worms may reach the aquatic environment they require; larvae of certain mussels extend the lives of their salmon hosts to complete their own development; and the fungus Cordyceps makes various insects and spiders locate the optimal location for its growth before killing the host and emerging from the remains.
And there are yet others that apparently exist for the sheer purpose of baffling humans! Asterophila is a snail that abandoned its shell to become a shapeless lump draining nutrients from starfish; acanthocephalans are an evolutionary offshoot of rotifers that decided to develop an industrial drill for a head and may now reach half a meter in size (rotifers are typically microscopic); pentastomids are creatures so alien that no one is sure exactly what they are (leading theories are that they're either highly derived crustaceans or distant cousins of all other arthropod groups); and facetotectans are a group so elusive that an adult specimen is yet to be identified (but curiously, facetotectans' affinities are well-documented thanks to their relatively mundane larvae). Many more examples of curious parasites exist, as there is no end to their diversity -- I can only stand in awe of their adaptations. Certainly, were I not human, then I should wish to be a parasite.
P.S. If you find the original version of the quote above, then congratulations, you've reached the bonus stage of this week's column! I highly recommend reading the Wikipedia article on the person in question, who is somewhat famous for being an Internet troll two thousand years before the Internet.