Vorticella long stalks

[Martin Parnham]

Hi folks -
Not very original but hopefully of passing interest.

My latest water sample from a new area contained Vorticella with notably long stalks. Initial mounts with my usual gentle cover slip squash, produced long headless stalks. I then made thicker water mounts (no squash, just the weight of the slip) and found intact specimens.
The depth of water makes focusing more difficult. As always the speed of contraction is amazing.

Presumably stalk length is partially species specific? Is it partially driven by the need to reach 'clear open' water for feeding and hence on the immediate environment surrounding the organism?
If so what might be the mechanism for this response?

Any thoughts gratefully received.



Brunel microscope SP300, Plan, Achro, Infinity, x10 objective, Oblique and Rheinberg oblique, Canon M50 II with direct image projection.

Martin

[Bruce Taylor]

In a revision of the genus from 1931, Noland & Finlay wrote:

The length of the stalk has long been used as a specific trait. While it is true that the stalk length of various species does tend toward a modal value, the individual variation is too great to justify placing much taxonomic value on the stalk length of any particular specimen. For instance, V. striata var. octava has a modal length near 100 micra, but varies from 20 to 300; V. nebulifera var. similis has a mode near 150 micra, with extremes of 50 to 800; while in V. campanula we found the mode near 300 micra and the limits at 50 to 4150! It is obvious, therefore, that the stalk length is highly variable within the species and cannot be used to any advantage in taxonomy.

A later revision of the genus (Warren, 1986) says pretty much the same thing. So, if you have morphometrics for a whole population, stalk length might be somewhat useful for taxonomic purposes, but stalk length of an individual specimen tells us very little.

You've raised some interesting questions, concerning possible factors that might affect stalk length. I don't have any information about that. A quick search turns up lots of research on contractility and stalk length, but I didn't see anything about length as an environmentally-driven trait (phenotypic plasticity). But I didn't go very deep. It might be an interesting research project for someone!

By the way, your images don't provide a close view of the pellicle, so we can't be sure that this is not a species of Pseudovorticella. Some members of that genus are virtually indistinguishable from Vorticella, especially at low magnification without stain. When in doubt, identify to family: Vorticellidae.

[Martin Parnham]

Very interesting references - thank you. I would never have found them.

4150 ! I have never seen any remotely that length. I suspect stalk length is determined by a complex interplay of factors, genetics, food availability, water flow, local topography, predation rates etc. I have found techniques on line to grow Vorticella. Perhaps a good place to start would be to try 'cultivate' them under controlled conditions and try altering factors to determine the effect on stalk length? But then sorting out the response mechanism is a whole new ball game!
Martin

PS - Also thank you for the ID info - I will attempt a more detailed look at the pellicle - I believe Pseudovorticella have small blisters?

[Bruce Taylor]

I believe Pseudovorticella have small blisters?

Some species (such as P. monilata) have conspicuous raised "tubercles", but others are quite smooth. All have an underlying pellicular pattern (the "silverline system") resembling brickwork, or a mesh; whereas, species of Vorticella have a silverline system consisting only of transverse lines. These patterns are difficult to see without silver impregnation, so identification to genus is not always possible in the light microscope. From Colin R. Curds et al., 1983:

In all respects, save one, the body and stalk of this genus resemble those of Vorticella from which it cannot be differentiated until impregnated with silver, which reveals a mesh-like pattern on the surface of the body quite unlike that of Vorticella.

In certain cases, identification below family is possible because of species-level characters. For instance, V. campanula has dark cytoplasm, filled with refractive granules, and a distinctively-shaped zooid (rumpled, baglike, with a heavy lip).