Larva-adult relationships in an ancestral dipteran: A re-examination of sensillar pathways across the antenna and leg anlagen of Chaoborus crystallinus (DeGeer, 1776; Chaoboridae) |
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Authors: | R R Melzer Julia Sprenger Daniela Nicastro Ulrich Smola |
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Institution: | Zoologisches Institut der Universit?t, Luisenstrasse 14, D-80333 München, Germany, DE
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Abstract: | In one of his classical studies on insect metamorphosis, Weismann compared the imaginal anlagen of the ancestral phantom
midge, Chaoborus, with those of advanced brachycerans. We have expanded his findings on the relationships between larval and imaginal organs
using electron microscopy and cobalt backfilling of the antenna and leg anlagen and the axonal trajectories of corresponding
larval sensilla. We show that both primordia are confluent with the larval antennae and ”leg” sensilla (an ancestral Keilin
organ), respectively. These fully developed larval organs represent the distal tips of the imaginal anlagen rather than separate
cell clusters. The axons of the larval antenna and leg sensilla project across the corresponding anlagen to their target neuromeres
within the central nervous system (CNS). Within the discs, nerves composed of these larval axons, developing afferent fibres
and efferences ascending from the CNS are found. Both the structure of the primordia and the axonal trajectories thus relate
the situation found in advanced brachycerans with that seen in more ancestral insects. In addition, the larval antennae, legs,
wings and even the eyes possess very similar afferent pioneer trajectories supporting the idea that the described pattern
is generally used in the ontogeny of sensory systems.
Received: 30 June 1998 / Accepted: 27 September 1998 |
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Keywords: | Imaginal disc Axonal trajectories Ultrastructure Chaoborus (Insecta Diptera) |
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