Molecular evidence for the gnathobasic derivation of arthropod mandibles and for the appendicular origin of the labrum and other structures |
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Authors: | A Popadi? Grace Panganiban Douglas Rusch William A Shear Thomas C Kaufman |
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Affiliation: | (1) Department of Biology and Howard Hughes Medical Institute, Indiana University, Bloomington, IN 47405, USA, IN;(2) Department of Anatomy, University of Wisconsin, Madison, WI 53706, USA, US;(3) Department of Biology, Hampden-Sydney College, Hampden-Sydney, VA 23943, USA, US |
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Abstract: | Mandibles are feeding appendages functioning as ”jaws” in the arthropod groups in which they occur. Which part of this appendage
is involved in food manipulation (limb tip versus limb base), has been used to suggest phylogenetic relationships among some
of the major taxa of arthropods (myriapods, crustaceans, and insects). As a way to independently verify the conclusions drawn
from previous morphological analyses, we have studied the expression pattern of the gene Distal-less (Dll), which specifies the distal part of appendages. Our results show, in contrast to the traditional view, that both insect
and crustacean adult mandibles are gnathobasic, handling food with the basal portion of the appendage. Furthermore, as is
evident by the reduction in the number of Dll-expressing cells in the later developmental stages, adult diplopod jaws are also gnathobasic. Thus, jaws of all mandibulates
(myriapods, crustaceans, and insects) seem to have a similar gnathobasic structure. We have also found that Dll is expressed in the labra of all arthropod taxa examined, suggesting that this structure is of appendicular derivation. Additionally,
the spinnerets and book lungs of spiders, long considered on other grounds to be modified appendages, express Dll, confirming this interpretation. This study shows that, in addition to their use in phylogenetic and population genetic studies,
molecular markers can be very useful for inferring the origins of a particular morphological feature.
Received: 12 January 1998 / Accepted: 23 March 1998 |
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Keywords: | Arthropods Mandibles Labrum Booklungs Dll expression |
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