The embryonic development of the amphipod crustacean Parhyale hawaiensis

The paucity of developmental, genetic, and evolutionary data available in non-model systems leaves critical questions regarding the tempo and mode of evolution in generating extant biological diversity unanswered. These questions can begin to be addressed by ‘gap-filling’ with new systems more closely related to systems currently in use. The insect and crustacean lineages are thought to be closely allied. Crustaceans are an enormously successful group, possessing a wide diversity of morphologies and life histories. My dissertation focuses on developing a crustacean ‘model system’ to fill a critical taxonomic gap for the functional study of embryogenesis.; I identified a crustacean species, Parhyale hawaiensis, suitable for laboratory culturing and embryonic analysis. Parhyale embryos are robust and resistant to environmental variations and thus are suitable for experimental manipulation. Parhyale embryos develop directly and hatchlings are morphologically similar to adults. I completed a detailed descriptive analysis of Parhyale embryogenesis, compiling data from in vivo description, nuclear DNA distribution, and two commonly used panspecific antibodies as molecular markers during segmentation and limb formation. Complete embryogenesis requires ∼250hrs at 26°C. I divided embryogenesis into 30 stages. Significant to further studies, the early cleavage program is total and holoblastic and generates an eight-cell embryo. The staging data generated for Parhyale will facilitate comparative analyses of embryonic development among Crustacea as well as divergent arthropod groups such as Insecta, Myriapoda, and Chelicerata.; The eight-cell stage of Parhyale is amenable to microinjection techniques. Lineage tracing experiments identified specific and invariant lineages that map uniquely to these eight blastomeres. The early establishment of distinct cell lineages will facilitate experimental manipulations of cell lineage and germ layers via microinjection and other perturbation techniques.; To explore the mechanism of ‘pair-rule’ patterning in segmentation, I cloned the Parhyale homolog of Drosophila hairy . In situ hybridization suggests a requirement for Ph hes in every segment. This is inconsistent with the two-segment periodicity patterning role of hairy in Drosophila . The Parhyale expression data suggests that ‘pair-rule’ patterning mechanisms may be restricted to the insect lineage. To assess the validity of this hypothesis requires analysis of hairy expression and other ‘primary pair-rule’ genes in additional arthropods.