Host Seeking and the Genomic Architecture of Parasitism Among Entomopathogenic Nematodes

Nematodes represent an especially abundant and species-rich phylum, with many free-living and parasitic species. Among the diversity of parasitic species is a guild of specialists known as entomopathogenic nematodes due to their unusual ability to quickly kill their hosts with the aid of pathogenic bacteria. Herein I discuss in detail the hallmarks of entomopathogenic nematodes and how they are different from other insect parasites. Further I explore their host-seeking behaviors, demonstrating their ability to detect insect hosts in complex soil environments and assess their odor preference profiles. I show that CO2 is a major driver of host seeking and that entomopathogenic nematodes detect CO2 using the same pair of conserved neurons that the fruit-dwelling Caenorhabditis elegans uses to detect and respond to CO2. I demonstrate dramatic differences in odor preference profiles and virulence capabilities, even between closely related nematodes. I discuss the role of genomic sequencing generally and more specifically in nematology, including how genomes are sequenced and analyzed and the types of characteristics that are most prominently assessed. This thesis concludes with a discussion of the genomic sequencing of entomopathogenic nematodes in the genus Steinernema and the clues these genomes provide regarding the genomic architecture of parasitism.