Variability in the number of abdominal leucokinergic neurons in adult Drosophila melanogaster.

Developmental plasticity allows individuals with the same genotype to show different phenotypes in response to environmental changes. An example of this is how neuronal diversity is protected at the expense of neuronal number under sustained undernourishment during the development of the Drosophila optic lobe. In the development of the Drosophila central nervous system, neuroblasts go through two phases of neurogenesis separated by a period of mitotic quiescence. Although during embryonic development much evidence indicates that both cell number and the cell fates generated by each neuroblast are very precisely controlled in a cell autonomous manner, after quiescence extrinsic factors control the reactivation of neuroblast proliferation in a fashion that has not yet been elucidated. Moreover, there is very little information about whether environmental changes affect lineage progression during postembryonic neurogenesis. Using as a model system the pattern of abdominal leucokinergic neurons (ABLKs), we have analyzed how changes in a set of environmental factors affect the number of ABLKs generated during postembryonic neurogenesis. We describe the variability in ABLK number between individuals and between hemiganglia of the same individual and, by genetic analysis, we identify the bithorax-complex genes and the ecdysone hormone as critical factors in these differences. We also explore the possible adaptive roles involved in this process. J. Comp. Neurol. 525:639-660, 2017.