How does the vortiella get energy?

Answer 1

A weedy little ditch runs along a country road about two miles from my home - a series of puddles occurs where water seeps from a nearby irrigation canal. The puddle I'm planning to sample is small, about a meter across and only about 10 cm deep at the deepest part. The surface is covered with a mat of duck weed, small floating plants with hanging rootlets.

This really is Biology in its simplest form. Dip up a quart jar of water along with a few duckweed plants and some bottom sediment. Head home for some casual microscopic exploration.

6:15 PMThe community of protists living on the duckweed rootlets reminds me of one observed 300 years ago by Antony Van Leeuwenhoek - the first person to really see, study, and record the microworld. His illustrations show many of the same organisms I am finding. One in particular, Vorticella, he describes in a most 17th century way: "These were the most wretched creatures ---they did struggle and stretch to free their tails, which then curled up again, serpentwise."

I'm focusing on a Vorticella, and except for an occasional recoil, the bell-shaped cell remains in the high magnification field, virtually filling it. Using the fine focus adjustment, I can view various levels through the cell. A rapidly beating band of cilia-stiffened membrane creates a feeding current that brings in bacteria. The bacteria funnel through a narrow sorting area where most are ejected. Focusing at another level shows a canal extending into the center of the cell from the sorting area. At the end of this short "gullet" a bubble is forming containing the bacteria selected for ingestion. Over a period of about 20 seconds the food vacuole pinches off joining a dozen or so older food vacuoles, their loads of bacteria in various stages of digestion.

6:20 PM:I'm observing a little clump of vorticellids encircling the duckweed root and wondering--how did they get there? It seems a reasonable guess that these clusters are related to some kind of reproductive process.

Reproduction in Vorticella poses an obvious problem--when the cell divides, who gets the stalk? Watching division begin, the answer isn't clear. Vorticella pulls in its feeding cilia and over a period of about 15 minutes division produces two spherical cells, each with a seemingly equal claim to the stalk. Then, one daughter gradually shifts position, so that its attachment is to one side of its sister giving it an orientation about 90 degrees to the stalk. At the cell°s posterior end a band of cilia develops. The cell elongates, its propellers rev up, and the daughter breaks free. Its newly generated swimming cilia now lead the way and the new Vorticella takes off like a torpedo. The bands of cilia that produced Vorticella's feeding currents are tucked in to what has now become the free-swimmer's posterior end. These migrant cells are known as "teletrochs".

The first time I saw this transformation I imagined these migrating daughters traveling to another part of the pond or puddle where they could became the founders of a new Vorticellacolonies, but how would that explain the clumps of individuals seen clustering on duckweed rootlets and elsewhere?

The daughter chase ...The daughter began a series of fast zig-zag passes through the drop of water on the slide. Running into the rootlet, it comes to a place where other vorticellids were attached and slows down, feeling its way along the rootlet. After a few minutes of this "searching behavior" it began spending its time at the base of the other vorticellids, including its sister, now the sole owner of the original stalk.

Next, the cell chooses a spot, attaches by its original posterior, looses its swimming cilia and produces a new stalk. Over the next 10 minutes the cell reopens its feeding cilia and transforms into a typical bell-shaped Vorticella.

This observation may help explain why vorticellids are often found in dense clusters. To see just how strong the stimulus of other vorticellids is in determining where teletrochs settles, I tried a simple choice experiment. I cut two short lengths of monofilament fishing line (4 lb test). One I taped to the jar containing and abundance of Vorticella so that a section of the line was submerged (let's call that the test line). The other I taped to a jar containing some paramecia, but no Vorticella(the control line). Both jars had an abundance of bacteria and small protists. 12 hours later the test line had quite a few attached individuals. Next, I clipped off the submerged sections of each line and added them to a petri dish culture of Vorticella. Within a few minutes teletrochs could be seen exploring regions where Vorticella had been attached. 12 hours later the test line was covered with Vorticella. The control line had just a few.

Although this choice experiment was rather crude, (we don't know if the same kinds of biofilms formed on each line) the result indicates that teletrochs exhibit a strong response to attached vorticellids, probably facilitated by chemical sensing.

Questions: The behavior I observed explains how clusters of vorticellids form. But, what exactly is the survival advantage of living in a group? What possible advantage is there in having similar cells all around you competing for the few bacteria that come drifting by? Is it "safety in numbers." Perhaps the springing action of a mass of vorticellids discourages predators. Are feeding currents amplified by the mass action of the group, perhaps drawing in bacteria from a much wider field? The down side is that a furry coating of vorticellids creates a protected habitat for small water animals such as oligochaete worms, ostracods, and small planarians. It appears that Vorticella has evolved a way to deal with intruders--periodically relocate, but that's a topic for another entry.