Sensory projection patterns of supernumerary legs and aristae in D. melanogaster

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Abstract
The central projection patterns of afferents from normal and duplicated legs and antennal aristae in D. melanogaster were established by horseradish peroxidase or cobalt labelling. Duplications were obtained genetically, by using l(1)ts726 and engrailed mutants, which are known to produce supernumerary legs and aristae, respectively. In normal legs, afferents from singly innervated mechanoreceptive (M‐) bristles terminate in the lateral and medial periphery of the corresponding leg neuromere. The medial periphery is also occupied by terminals of multiply innervated chemoreceptive (C‐) bristles; another target of C‐bristles is the anterior margin of the neuromere. The sensory projection patterns of homologous M‐bristles on different leg segments are overlapping, suggesting that terminals are not ordered according to the proximo‐distal location of their cell bodies on the leg. The sensory projections of duplicated legs or aristae overlap the corresponding normal projections. However, when stimulating supernumerary legs in the proboscis extension paradigm, the frequency and intensity of reflex activity are significantly reduced compared to normal legs. These data suggest that normal and supernumerary afferents compete with one another in a subtle way which is not accompanied by gross morphological changes of the projection patterns.