Embryonic and postembryonic neurogenesis in the ventral nerve cord of the freshwater crayfish Cherax destructor

Previous studies of neurogenic activity in the thoracic neuromeres of indir ect developing crustaceans indicated that the temporal patterns of neurogen esis can be correlated with the appearance of the thoracic appendages durin g larval and metamorphic development. To test further the idea that; the te mporal patterns of neurogenesis in crustaceans are related to their life hi stories, we examined neurogenesis in the ventral nerve cord of a direct dev eloping crustacean, the freshwater crayfish Cherax: destructor, whose life history contains neither larval stages nor metamorphoses. Neurogenesis was examined using the in vivo incorporation of bromodeoxyuridine into DNA. Dur ing late embryonic development the thoracic neuromeres of the crayfish cont ain arrays of mitotically active neuroblasts similar to those previously de scribed in the spider crab; and lobster The arrays in the crayfish abdomen are, however, greatly reduced compared with those of the thorax. On hatchin g, both the thoracic and abdominal appendages of C. destructor are capable of movement. The pleopods, however, do not beat rhythmically until the seco nd postembryonic stage whereas the pereiopods are not used in coordinated w alking movements until the third stage. An examination of the time course o f neurogenesis in the ventral nerve cord revealed that neurogenic activity in each neuromere ceases during or before the moult to the developmental st age in which its segmental appendage is first used in coordinated movements . These findings :indicate that the patterns of neurogenesis in crustaceans are indeed related to the maturation of :the segmental appendages and, in particular, to the maturation of motor behaviours. (C) 2001 Wiley-Liss,Inc.