Living and Adapting to Its Own Habitat - Building the Most Complex Structure on Earth - page 222

Forced crowding of solitarious phase locusts
leads to:
Smell and sight of other locusts

Hind legs being touched

Increase in serotonin

Block serotonin
or
prevent it
being made

Inject serotonin
or
drugs that mimic
its effect

GO

STOP

SoIitarious
behavior

Gregarious
behavior

Figure 4.13 Changes from solitarious to gregarious behavior occur rapidly and are mediated
by serotonin. Diagrammatic summary of the behavioral gregarization pathway and the role of
serotonin is shown.
Source : From Burrows et al. (2011)

comes from. The gregarious behavior is experimentally demonstrated to be related
to changes in the activity of the flight-related neurons. So, for example, spontane-
ous electrical activity of the flight-related tritocerebral commissure dwarf (TCD)
interneuron is stronger and gregarious than solitarious locusts ( Fuchs et al., 2003 ).
The olfactory (and visual) stimuli in the form of electrical spike trains are trans-
mitted from the sensory organs to be processed in labyrinthine neural circuits already
described in detail ( Bargmann, 2006; Laurent et al., 1998 ). As mentioned earlier, the
most characteristic changes related to the transition from the solitarious to the gre-
garious phase are observed in the function of neurons and neural circuits. Among the
mentioned dramatic changes in the synthesis of the neurotransmitters and neuromod-
ulators in the nervous system, the most conspicuous and the most relevant seem to
be the rapid increase of serotonin in the thoracic ganglia in the first 1-4 h following
stimulation. This increase in the serotonin level induces gregarious behavior and the
intensity of this gregarious behavior is proportional to the increase in serotonin level.
This neurotransmitter effect is verified by the experimental administration of seroto-
nin into the thoracic ganglia that induces the transition to the gregarious phase even
in locusts that have never encountered other locusts ( Figure 4.13 ). To the contrary,
the mediator of the serotonin action prevents transition to gregarious phase in locusts
by blocking the serotonin synthesis or serotonin receptor ( Burrows et al., 2011 ).
Besides the serotonergic pathway, the dopaminergic pathway is also important,
most likely synergistic, in establishing gregarious behavior in locusts and the injec-
tion of DA also induces gregarious behavior ( Burrows et al., 2011 ; Ma et al., 2011 ).