Locusts Provide Clues to Insect Mushroom Body Function

The insect mushroom bodies are sensory integration and learning and memory centers that display morphological plasticity on both individual and evolutionary timescales; mushroom bodies and their intrinsic neurons restructure in response to individual behavioral experience [Withers et al., 1993; Seid and Wehner, 2009], while across the insects particular mushroom body morphologies are linked to species-specific behavioral ecologies [Farris, 2005]. It is therefore not surprising to see significant differences in mushroom body morphology associated with the dramatic behavioral differences of gregarious and solitarious locusts. However, given the widely held belief that the mushroom bodies function predominantly as olfactory learning and memory centers [Davis, 2005], the disconnect between their size and that of the primary olfactory neuropils, the antennal lobes, seems somewhat anomalous. Rather, these results suggest that whatever functional demand the mushroom bodies of gregarious individuals have expanded to meet, it is unlikely to be solely associated with their role as olfactory processing centers. Ott and Rogers suggest another challenge of life in the swarm that may impact mushroom body function: the need to extract salient sensory cues such as those produced by food sources and potential mates from the constant barrage of stimuThe 2 phases of the desert locust Schistocerca gregaria are very different beasts. Solitarious individuals are slow-moving, nocturnal and cryptically colored, avoiding contact with conspecifics except for mating. But when crowded, sensory stimulation from the jostling bodies causes these formerly retiring creatures to transform into a gregarious phase characterized by flashy aposematic coloration, high locomotor activity and active aggregation into day-flying swarms numbering hundreds of millions of individuals [Simpson et al., 1999, 2001; Anstey et al., 2001]. A new study by Ott and Rogers [2010] demonstrates that the brains of the 2 phases are as different as their behaviors, with gregarious individuals having brains 30% larger than their solitarious counterparts. Within the brain, higher brain centers such as the mushroom bodies are disproportionally larger in gregarious locusts, while in solitarious locusts primary sensory neuropils such as the antennal lobes are larger. Solitarious individuals thus seem to be geared towards lower-level sensory processing, perhaps increasing their sensitivity to visual and odor cues. Gregarious individuals on the other hand prioritize higher integration, perhaps necessitated by their extremely generalist feeding ecology and the intense intraspecific interactions they experience within the gregarious swarm. Published online: January 20, 2011