Mechanosensory-induced behavioural gregarization in the desert locustSchistocerca gregaria

Abstract

Locusts have the remarkable ability to change between two morphologically, physiologically and behaviourally distinct forms depending on their population density (Uvarov, 1966). This density-dependent phase polyphenism is an extreme form of variation common to many species that migrate, form seasonal herds or are otherwise subject to fluctuating population densities (Dingle, 1995). Locusts in the solitarious phase are cryptic in appearance and behaviour, occur at very low population densities and actively avoid each other. Conversely, locusts in the gregarious phase are brightly coloured as nymphs, more behaviourally active and aggregate together into bands, which may ultimately form migrating swarms consisting of millions of individuals (Uvarov, 1966;Simpson et al., 1999). The transition between the two extreme phases is a multistage process, with some changes in morphology and physiology taking several stadia or even generations to complete (Pener, 1991;Applebaum and Heifetz, 1999). By contrast, many behaviours change extremely rapidly. Solitarious locusts acquire most of the behavioural characteristics of gregarious phase locusts within only 4·h of crowding including, critically, the propensity to aggregate and thus reinforce the gregarizing stimuli provided by other locusts (Ellis, 1963;Gillett, 1973;Roessingh and Simpson, 1994;Bouaïchi et al., 1995). These rapid changes make locust phase change a potentially valuable tool in understanding neuronal plasticity and its behavioural consequences.Olfactory and visual stimulation provided by other locusts promotes behavioural gregarization when presented together but has little effect individually. An extremely potent stimulus, however, is repeated physical contact produced by either touching or jostling, which elicits rapid and full behavioural gregarization in the absence of any other sensory stimuli (Roessingh et al., 1998;Hägele and Simpson, 2000). This mechanical stimulation must be directed to the middle or hind legs in order to have any effect, with the hind femur being by far the most effective site at which to elicit gregarization (Simpson et al., 2001 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 locust foraging gene

“…A remarkable example of environmentally induced behavioral plasticity can be found in locusts. In the desert locust (Schistocerca gregaria), solitary-phase locusts are cryptic in physical appearance and behavior (Rogers et al, 2003). They actively avoid contact with other locusts (Roessingh et al, 1993), and are relatively sedentary (Simpson et al, 1999).…”

The neurogenetics of group behavior inDrosophila melanogaster

“…As mentioned earlier, these two modalities are crucial for D. melanogaster social network formation and collective behavior (Ramdya et al, 2015;Schneider et al, 2012b). Similarly, in locusts, tactile stimulation of the legs is responsible for the transition from solitary to gregarious states, resulting in the formation of massive collectively marching bands (Rogers et al, 2003;Simpson et al, 2001). Touch interactions also direct the dynamics of dense human crowds (Moussaïd et al, 2011).…”

“…For example, ants build complex colonies that span many kilometers (Hölldobler and Wilson, 1990) and fish aggregate into large schools that can dissuade or facilitate escape from predators . Although we now have a good understanding of behavioral algorithms that give rise to group action (Rogers et al, 2003), very little is known about their underlying neurogenetic mechanisms. This is partly due to the complexity of natural environments: constantly changing visual, auditory, olfactory, gustatory and tactile features make it difficult to determine which cues and biological sensors serve to link individuals with one another.…”

Application of Grasshopper Optimization Algorithm for Constrained and Unconstrained Test Functions

“…They almost eat all the vegetation which comes in their path during their movement. When they become adult from nymph, they form a swarm in air and then they migrate over a very large distance [22,23].…”