Date of Completion
Tribolium castaneum; Tardigrada; Panarthropoda; Evolution; RNA interference
Elizabeth L. Jockusch
Carl D. Schlichting
David L. Wagner
Steven Q. Irvine
Field of Study
Ecology and Evolutionary Biology
Doctor of Philosophy
In Chapter 1, the roles of genes that specify antennal identity in Drosophila melanogaster were investigated in the flour beetle Tribolium castaneum. Antenna-to-leg transformations occurred in response to RNA interference (RNAi) against homothorax, extradenticle, spineless and Distal-less. However, for homothorax/extradenticle RNAi, the extent of transformation along the proximodistal axis differed between embryogenesis and metamorphosis. In chapter 2, the metamorphic roles of the Hox genes, extradenticle, and homothorax were compared in T. castaneum. homothorax/extradenticle RNAi and Hox RNAi produced similar body wall phenotypes but different appendage phenotypes. These results suggest that Hox genes require extradenticle and homothorax to specify sclerite identities in the thorax and abdomen during metamorphosis. On the other hand, the Hox genes act independently of extradenticle or homothorax to specify appendage identities along the body axis, while extradenticle and homothorax do not require Hox genes to impart proximal identity to appendage podomeres. In Chapter 3, the body plan of the tardigrade Hypsibius dujardini was characterized using anti-β-tubulin immunostaining and phalloidin staining. These methods revealed differences in the nervous system and musculature that make each segment unique. In Chapter 4, the embryonic role of the gene Distal-less was investigated in H. dujardini. It is expressed in the pharyngeal stylets and across the entire proximodistal appendage axis. The uniform expression of Distal-less in developing appendages is consistent with the lesser degree of morphological regionalization exhibited in tardigrade appendages relative to arthropod appendages.
Smith, Frank W. III, "Conservation and Diversification of Appendage Identity Specification Mechanisms Along the Anteroposterior and Proximodistal Axes in Panarthropoda" (2013). Doctoral Dissertations. 161.