Ground plan of the insect mushroom body: functional and evolutionary implications.
In most insects with olfactory glomeruli, each side of the brain possesses a mushroom body equipped with calyces supplied by olfactory projection neurons. Kenyon cells providing dendrites to the calyces supply a pedunculus and lobes divided into subdivisions supplying outputs to other brain areas. It is with reference to these components that most functional studies are interpreted. However, mushroom body structures are diverse, adapted to different ecologies, and likely to serve various functions. In insects whose derived life styles preclude the detection of airborne odorants, there is a loss of the antennal lobes and attenuation or loss of the calyces. Such taxa retain mushroom body lobes that are as elaborate as those of mushroom bodies equipped with calyces. Antennal lobe loss and calycal regression also typify taxa with short nonfeeding adults, in which olfaction is redundant. Examples are cicadas and mayflies, the latter representing the most basal lineage of winged insects. Mushroom bodies of another basal taxon, the Odonata, possess a remnant calyx that may reflect the visual ecology of this group. That mushroom bodies persist in brains of secondarily anosmic insects suggests that they play roles in higher functions other than olfaction. Mushroom bodies are not ubiquitous: the most basal living insects, the wingless Archaeognatha, possess glomerular antennal lobes but lack mushroom bodies, suggesting that the ability to process airborne odorants preceded the acquisition of mushroom bodies. Archaeognathan brains are like those of higher malacostracans, which lack mushroom bodies but have elaborate olfactory centers laterally in the brain.
Strausfeld
Nicholas J
NJ
Arizona Research Laboratories, Division of Neurobiology, University of Arizona, Tucson, AZ 85721, USA.
Sinakevitch
Irina
I
IBDML-UMR 6216, Case 907 Parc Scientifique de Luminy, 13288 Marseille, Cedex 9, France.
Brown
Sheena M
SM
Arizona Research Laboratories, Division of Neurobiology, University of Arizona, Tucson, AZ 85721, USA.
Farris
Sarah M
SM
Department of Biology, West Virginia University, Morgantown, WV 26506, USA.
D000818:Animals; D005075:Biological Evolution; D007313:Insecta / Q000502:physiology* / Q000648:ultrastructure*; D024521:Mushroom Bodies / Q000502:physiology* / Q000648:ultrastructure*; D010802:Phylogeny