51.3 Thursday, Jan. 5 Development of Hypsibius dujardini (Tardigrada) lobopodal appendages and the origin of the arthropod appendage SMITH, FW*; TENLEN, JR; GOLDSTEIN, B; JOCKUSCH, EL; University of Connecticut; University of North Carolina; University of North Carolina; University of Connecticut firstname.lastname@example.org
The unparalleled success of Arthropoda can be partly attributed to the ventral appendages defining this phylum, which exhibit an incredible diversity of both form and function even within single individuals. Although appendage diversity within Arthropoda is based on a jointed-appendage groundplan, evidence suggests arthropods evolved from an ancestor with homonomous unjointed lobopodal appendages. This ancestral morphology is retained in the arthropod sister phylum Onychophora and also the Tardigrada, which together with Arthropoda comprise the Panarthropoda. Across Arthropoda, the leg gap genes Distal-less, dachshund, extradenticle, and homothorax act as master regulators of appendage patterning. These genes have recently been implicated in the development of onychophoran appendages, but no published genetic data concerning tardigrade appendage development is available. Investigations of tardigrade appendage development would allow phylogenetic reconstructions of ancestral appendage generating mechanisms, and provide insight into the developmental genetic changes underlying the transition from a lobopodal appendage to the segmented arthropod appendage. Here we present results of both morphological and genetic investigations of appendage development for the tardigrade Hypsibius dujardini. Orthologs of Distal-less, dachshund, and extradenticle have been cloned from embryonic H. dujardini cDNA. Preliminary results of an investigation into both the function and expression patterns of these genes during H. dujardini embryogenesis will be presented, and the implications for the evolution of the arthropod appendage will be explored.