Rogers, S.M., Despland, E., Dodgson, T., Burrows, M., Simpson, S.J. & Matheson, T. 2003. Mechanisms of mechanosensory induced behavioural gregarization in the Desert Locust Schistocerca gregaria. Journal of Experimental Biology 206:3991-4002.
Desert locusts show an extreme form of phenotypic
plasticity, changing between a cryptic solitarious phase
and a swarming gregarious phase that differ in many
aspects of behaviour, physiology and appearance.
Solitarious locusts show rapid behavioural phase change
in response to tactile stimulation directed to the hind
femora. Repeatedly touching as little as one quarter of the
anterior (outer) surface area of a hind femur produced
full behavioural gregarization within 4·h. Solitarious
locusts have approximately 30% more mechanosensory
trichoid sensilla on the hind femora than do gregarious
locusts but have similar or fewer numbers of sensilla
elsewhere on the legs. Tactile stimulation of a hind femur
in solitarious locusts that had been restrained so that they
could not move their legs failed to induce any behavioural
gregarization. Patterned electrical stimulation of
metathoracic nerve 5, which innervates the hind leg,
however, produced full gregarization in restrained locusts.
Our data show for the first time that the gregarizing
signal combines both exteroceptive and proprioceptive
components, which travel in both nerves 5B1 and 5B2, and
provides us with a powerful experimental method with
which to elicit and study neuronal plasticity in this system.
Acetic acid odour, a strong chemosensory stimulus
that activates the same local processing pathways
as exteroceptive stimuli, failed to elicit behavioural
gregarization, suggesting an early segregation in the
central nervous system of the mechanosensory signals that
leads to gregarization.
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