Woodlice Choice Chamber Experiment

Woodlice may look like a type of millipede or beetle, but they are in fact related to crabs and other crustaceans! These small and abundant creatures (they live everywhere except for Antarctica) are ideal for observing animal movement using techniques such as the choice chamber experiment. All living beings constantly adjust to their environment to survive. This adaptation happens through responses to external and internal stimuli and ensures homeostasis. Woodlice change their movement pattern when responding to stimuli such as temperature or food sources in their environment, it is therefore easy to recreate their ideal habitat to observe their behaviour due to them being tiny minibeasts!

Taxis and kinesis

A taxis is a simple type of movement response by a motile organism. The direction of the stimulus determines the direction of the movement. Taxes are very similar to another kind of response by plants called tropisms. In a tropism response, plants can only change the direction of their growth either towards or opposite the direction of the stimulus because plants can’t move. In taxis, however, a motile organism can move away from unfavourable stimuli (negative taxis) or towards a favourable stimulus (positive taxis).

The type of taxis is defined according to its originating stimulus.

Both taxis and kinesis are interlinked behavioural responses, they respond to stimulus and are found in living motile organisms like animals and insects. Kinesis is more dependent on taxis, see below to understand why.

Difference between taxis and kinesis

A kinesis is a distinct type of behavioural response from a motile organism. Unlike taxis, a kinesis response does not involve changing the direction of movement according to a stimulus direction but instead changing the organism’s speed of movement and the rate of direction change. This response can be important when reacting to less directional stimuli like temperature or humidity and doesn’t vary in space in clear gradients.

In a kinesis-type response, when an organism senses that it has temporarily entered a more unfavourable location, it will increase its speed and rate of turning to exit the space. However, if the organism continues in such adverse surroundings, it will decrease its turning rate (direction change); thus, moving in long straight lines and increasing the chances of reaching a more suitable environment, where the temperature might be milder.

The movement of woodlice

Woodlice are crustaceans often used as examples when investigating animal movement responses. These animals can display both taxis and kinesis-type responses when searching for ideal living conditions in their habitat.

Woodlice also display kinesis-type responses when searching for ideal temperature and humidity conditions. Unlike light sources, these stimuli can be harder to pinpoint and may not vary in clear gradients, making it harder to inform a directional response. These stimuli lead to random movement responses from woodlice seeking better environmental temperature and humidity conditions to increase their survival chances.

In a kinesis response, woodlice move faster if the temperature drops below or rises above a specific optimal range in their current location. The higher speed increases the chance of the woodlice exiting the unfavourable area more quickly to another area where the temperature is more favourable and in the optimal living range.

The same happens when woodlice encounter a dry environment. Woodlice prefer damp areas because they lose water content from their bodies in dry conditions. When moving from a damp area to a dry one, woodlice moves faster and changes direction more often to return to a damp area.

All these behavioural strategies will increase the chances of woodlice or any other animal spending more time in favourable conditions (damp and mild temperature) than unfavourable ones (dry, extreme temperatures).

Fig. 2: Woodlice kinesis response to humidity conditions

What is a choice chamber?

Choice chambers are artificial structures used to investigate animal behaviour. Any small motile organism can be stimulated by different environmental conditions, and their movement response is analysed using this method. These structures allow us to know what environmental conditions animals prefer when looking for suitable habitats.

Choice chambers are enclosed in designed environments with several linked compartments within a large plastic petri dish, simulating desired environmental conditions. Animals like woodlice are placed in these structures, and their behaviour is assessed by analysing their movement through these compartments. A woodlice’s preference for certain habitat conditions reflects in their choice of chamber division that most resembles their ideal natural environment.

A choice chamber can be made with both dry and damp compartments to investigate the influence of humidity on woodlice movement. The same can be achieved for light stimulation simply by covering part of the dish from any light source, thus creating a dark compartment within the chamber. The animals, like woodlice, are then dropped into the structure and start moving around. After experiencing the different stimuli, the organisms will gravitate towards the more suitable environment through taxes and kineses responses.

Fig. 3: An example of a choice chamber

Woodlice choice chamber experiment control

It is possible to replicate several different combinations of compartments in a choice chamber depending on which environmental factors and how many are being assessed. However, an empty control chamber must always be present to ensure that the stimuli influence animals’ movements and that woodlice are evenly distributed in an empty chamber.

Woodlice choice chamber experiment results

Counting the number of woodlice within each chamber determines the choice chamber results. The compartment with the highest number of animals likely simulates that animal’s most desirable condition in the wild for that particular environmental factor.