Kinesis and Taxis

• kinesis- Orientation without respect to the direction of the stimulus
  • orthokinesis- A change in the rate of movement
  • klinokinesis- A change in the rate of turning
• taxis- A directed response to the stimulus.

Pillbugs (Porcellio scaber) in a humidity gradient move at random with respect to the gradient (see movies below). However, they move more quickly in dry areas which causes them to move out of the unsuitable environment. Once they find themselves in a high humidity environment they slow down and become motionless. This type of orientation is a kinesis. In particular, this is an orthokinesis (a change in the rate of movement).

Response of Pill Bugs to High and Low Humidity Environments

The top half of the container is a high humidity environment. The Bottom is a low humidity environment.
Note that animals stay in the high humidity environment. (Original: 1 frame/60 seconds)

One animal was placed in a moist habitat, the other in a dry environment. Note the obvious
differences in their rate of movement (Original: 1 frame/5 sec)

A taxis, on the other hand, is a directed response. Examples of taxes are shown below: