Characterization of molting deficient mutants in the necromenic nematode Pristionchus pacificus

In 1997, Aguinaldo et al. proposed that all molting animals be placed in a single super-phyla based on a shared attribute of shedding the larval cuticle. Given the recent integration of all molting animals into the same clade it has become necessary to re-evaluate the evolution of this clade-defining characteristic. Two of the most well known phyla within this group, the arthropoda and the nematoda, have seen extensive studies on molting in the models Drosophila melanogaster and Caenhorabditis elegans respectively. In this thesis we show an initial evaluation of the evolution of molting within ecdysozoans. We begin by evaluating the evolutionary relationships between the most conserved inaugural member of the ecdysozoan molting pathway, nhr-23/Hr46, in Chapter 1. From this evaluation we can start to outline the studies necessary to understand how molting has evolved across the super-phyla. In Chapter 2, we address the distinct lack of understanding of the hormonal requirements for molting in one of the two well studied ecdysozoan models, C. elegans. We set in motion the characterization of endocrine signaling in nematode molting by investigating the source-specific requirement for cholesterol, an endocrine pre-cursor found within all ecdysozoans. Finally, in Chapter 3 we initiate an attempt at understanding how evolutionary changes which affect the process of molting have occurred within the nematoda. We look at sterotypic molting behaviors, combined with genetic and molecular analysis, to highlight how heterochronic changes in the relationship between other developmental events can lead to relative differences in molting between distantly related nematodes.