TY - JOUR
T1 - Larva-adult relationships in an ancestral dipteran
T2 - A re-examination of sensillar pathways across the antenna and leg anlagen of Chaoborus crystallinus (DeGeer, 1776; Chaoboridae)
AU - Melzer, Roland R.
AU - Sprenger, Julia
AU - Nicastro, Daniela
AU - Smola, Ulrich
PY - 1999
Y1 - 1999
N2 - 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.
AB - 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.
KW - Axonal trajectories
KW - Chaoborus (Insecta, Diptera)
KW - Imaginal disc
KW - Ultrastructure
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UR - http://www.scopus.com/inward/citedby.url?scp=0032991070&partnerID=8YFLogxK
U2 - 10.1007/s004270050232
DO - 10.1007/s004270050232
M3 - Article
C2 - 10022953
AN - SCOPUS:0032991070
SN - 0949-944X
VL - 209
SP - 103
EP - 112
JO - Development Genes and Evolution
JF - Development Genes and Evolution
IS - 2
ER -