Defense posture and leg-position learning in a primitive insect utilize catchlike tension

Area of Science:

• Insect behavior
• Neuroethology
• Biomechanics

Background:

• The weta (Orthoptera: Stenopelmatidae), a primitive New Zealand insect, was used to investigate learned motor control.
• Understanding the mechanisms of posture adjustment in invertebrates provides insights into fundamental biological principles.

Purpose of the Study:

• To examine the capability for conditioning of leg position in wetas.
• To determine the reinforcement mechanism involved in posture conditioning, using loud sound as an aversive stimulus.

Main Methods:

• Electromyographic recordings were performed during conditioning trials.
• Leg position conditioning was achieved by coupling posture changes to the cessation of loud sound.

Main Results:

• A majority of wetas stably occupied a conditioned metathoracic tibial position.
• This conditioned position, in either flexion or extension, was linked to turning off the sound.
• Steady tensions were produced in the legs, but without accompanying electromyographic activity.

Conclusions:

• Wetas can learn to adjust their leg posture based on auditory aversive reinforcement.
• The absence of electromyographic activity suggests the use of a peripheral catchlike mechanism for posture maintenance.