Variability in the Structure of an Identified Interneurone in Isogenic Clones of Locusts

Several studies have shown that there can be considerable variability in the morphology of identified neurones. In a recent investigation (Pearson & Goodman, 1979) a great degree of variability was observed in the axon branching patterns of the descending contralateral movement detector (DCMD) interneurones of locusts. Corresponding to the variation in the structure of DCMD was a large variation in the synaptic connections made by this interneurone; the absence of a monosynaptic connection always correlated with the lack of the appropriate axonal branch of DCMD. Since this variability could be related to genotypic differences, we investigated the structure and synaptic connections of DCMD in individuals from several different isogenic clones of the locust Schistocerca gregaria. Within a single group of clones the variability in the axonal branching patterns and synaptic connections of DCMD was generally less than that between different clones or in sexually reproduced control animals. More significantly, a few of the clonal groups had consistently unique branching patterns and concomitant synaptic connections. Nevertheless, there was still some variability in the structure of DCMD within each clone. We conclude from these observations that differences in genotype can influence the morphology of individual neurones at the relatively refined level of axonal branching patterns and consequently the neurone's synaptic connections. However, due to the variability of DCMD structure within a single clone, epigenetic factors must also determine the pattern of axonal branching.