Re: origin of behavior in unicellular organisms?

You may not know of any even *more* animal-like feature possessed by a 
protist: an eye-like structure in a rare marine dinoflagellate called 
Erthythropsidinium.  Its geometry suggests optics capable of projecting an 
image onto its smooth, retina-like surface (actually, a modified 
chloroplast).  
Now one knows what this so called "ocellus" is used for or how its light 
signals are integrated into the cell behavior of this predatory cell.  Some 
have even reported microtubules that run from the ocellus to the nucleus.

Despite this profound ignorance and mystery, we do know a fair bit about 
Paramecium.  These and other ciliates have been nicknamed "swimming neurons" 
because their behavior is controlled by neuron-like changes in their ion 
channels (K, Na, Ca, etc).  The idea for cell reversal is this:  mechano-
receptors, when deformed by physical forces, allow ions (either K or Ca, I 
forget) into the cell, which ultimately triggers a "wave" of increased Ca 
concentration in the cytoplasm, which directy causes the cilia to reverse 
their beating pattern.  Simple!  (Such details are determined by watching 
the behavior of ion channel mutants, and isolating the damaged protein.)

Calcium is also involved in the defensive or offensive discharge of weapons 
called either trichocysts or toxicysts.  The latter are found in the famous 
predator of Paramecium, Didinium.  If a cell is held firmly in place with a 
micropipette and its apical cone is injected with a bit of Ca by a smaller, 
sharp micropipette, the toxicysts are ejected.  Evidently the concentration, 
duration and location of a Calcium pulse within the cytoplasm can effect 
various behaviors.

I hope this gives you a sense of this research.  Cheers, Dean Jacobson