Meeting Abstract

P1.61  Friday, Jan. 4  The Tardigrade Hypsibius dujardini and Body Plan Evolution within Panarthropoda SMITH, FW*; GOLDSTEIN, B; JOCKUSCH, EL; University of Connecticut; University of North Carolina; University of Connecticut frank.smith@uconn.edu

The panarthropodan lineage includes the phyla Arthropoda, Onychophora and Tardigrada. Arthropods are known for their jointed appendages and an incredible degree of tagmosis. Ancestral panarthropodans had homonomous lobopodal leg-like appendages and a much lower degree of tagmosis. Like onychophorans, tardigrades retain the ancestral lobopodal appendage type. Tardigrades also show the lowest degree of tagomosis of the extant panarthropodan phyla. Here we present results emanating from an EDEN sponsored research exchange to develop both in-situ hybridization and immunostaining protocols for the tarigrade species Hypsibius dujardini. Using a metazoan cross-reactive α-tubulin antibody, we have found that H. dujardini adults have a rope-ladder like nervous system with segmental commissures like arthropods, but unlike onycophorans. Using a combination of DAPI and phalloidin staining, we have found that the legs of H. dujardini adults lack intrinsic musculature, like onychophorans, but unlike arthropods, which have intrinsic musculature in their appendages. Finally, we have cloned orthrologs of the candidate leg patterning genes Distal-less (Dll), extradenticle and dachschund and have discovered a single homothorax ortholog in preliminary genomic reads. Dll in-situ hybridization shows expression throughout the developing limb bud, unlike in onychophorans and arthropods, where Dll expression becomes more restricted to the distal appendage domain. These results and preliminary in-situ hybridization results for the other leg patterning gene orthologs will be presented and the implications for panarthropodan body plan evolution discussed.