BY ALPER ÖZKAN (MSN/PhD)
d_ozkan@ug.bilkent.edu.tr
Well, that stream-of-consciousness Ebola rant was surprisingly cathartic—after getting that out of the way, my mood and fortunes took a sudden turn for the better, and the Philosophy Day proceedings (which doubled as a de facto day off) sure helped things along. To be frank, though, what really impressed me was the sheer breadth of knowledge that just about everyone in the philosophy department had—over here, you tend to specialize in a narrowly defined field, so you’re not even a biologist or physicist, but a cancer biologist or a solar cell physicist, and you have a rather limited grasp on things that are not your specialty. I have little experience in histology, for example, so every tissue section looks to me like someone ran a small, furry critter through a blender, but my colleagues can tell what’s what and where’s where at a glance (and they, in turn, would be put on the spot if asked about, say, Fisherian runaways). But the folks over at Philosophy Day were switching between ancient, medieval and modern philosophies at such a pace that I was getting vertigo—I guess I’ll just chalk it up to my inexperience.
But I digress—the fact of the matter is that I’m in a good mood, so I’ll be talking about parasites, and, why yes, parasites are definitely the thing to talk about when you’re in a good mood. Flesh-boring maggots and worm-ridden fishes, nematodes turning ants into fruit dishes, wasp mimics of bees that eat nest-siblings, these are a few of my favorite things♪
Ahem.
The topic of the day is flukes, so let’s get the most popular out of the way first: Lancet liver flukes alter ant behavior to get them to climb onto blades of grass, where they’re likely to be eaten by their final hosts, grazing ruminants. Diplozoon and certain didymozooids display a complete, irreversible sort of monogamy, since the worms literally fuse with each other in such a way that the male reproductive channel of one worm opens directly into the female reproductive channel of the other, and vice versa (that’s the case in Diplozoon; didymozooids may have different arrangements in their genital junctions—some even display gonochorism—and there’s at least one species that can fuse into itself). Ribeiroia makes frogs grow extra or malformed legs so that birds can hunt them better, Leucochloridium turns the eyes of snails into pulsating, brightly-colored lumps so that birds can hunt them better, and there’s also a fluke that damages the foot of its cockle host to prevent it from burrowing, so that birds can hunt it better.
You know, sometimes I wonder whether some of these bird parasites are really bird mutualists in disguise. It’s an unlikely prospect, yes, but has anyone done a cost-benefit analysis on them? I know that heavy parasite loads can get nasty, but I also know that parasites regulate their own populations in hosts, and these birds really are getting an all-you-can-eat buffet there. I’m pretty sure I could tolerate a fluke or two, if those flukes delivered cercaria-encysted rib cuts to my front door every day.
And speaking of cercaria, I now remember that they were why I wanted to write about flukes in the first place. Flukes, like many other parasites, pass through several life stages specialized for infiltrating and surviving in their multiple hosts, and the cercaria is the penultimate stage, usually tasked with finding either the definitive host (in which the cercaria will develop into the adult) or an intermediate host that will be eaten by the definitive host (in which the cercaria encysts until the intermediate host is consumed). Some cercariae, like these of Leucochloridium, have their previous hosts ingested by the next, while the lancet liver fluke relies on the fact that ants sometimes eat the cercaria-ridden balls of slime that snails secrete, and the cercariae of some flukes can choose to encyst on water plants to be picked up by grazing animals—but others, such as those of the infamous blood fluke Schistosoma, are active swimmers that must find and penetrate their quarry. Some simply home in onto their host and drill their way in; others have long tails that entangle them with fish.
And then there is the Rattenkönig cercaria.
The Rattenkönig is a phenomenon where the tails of multiple rats, assisted by the filth that these rodents are often forced to live in, entangle with each other, creating a hydra-like animal with multiple bodies joined together by a Gordian knot of tails—this is likely the inspiration behind the seven-headed titular character in “The Nutcracker and the Mouse King” (no, not the nutcracker). The Rattenkönig cercaria is similar, except that instead of seven, it combines the might of up to seven hundred bodies—the gigantic mass of cercariae not only maneuver expertly by coordinating the beats of their intertwined tails, but also look like a tasty little morsel to any nearby fish. Once attacked, the cercariae detach in the mouth of their would-be predator, and are free to enter and encyst within.
My favorite cercariae, though, are of the cystophorous type, which hide in their own hollowed, spherical tails when startled. That’s cute in a way that you wouldn’t expect from something that finds the act of drilling into another living creature to be its sole purpose in life.