Parasites outnumber free-living species, perhaps 4 to 1, and they play important roles in natural ecosystems. Parasites may directly harm humans or those species that humans depend on, or they may indirectly help humanity by controlling the abundance of pest species.
Based on the abundance and diversity of parasites, it is clear that parasites evolved from free-living ancestors on many occasions in the past. However, the remarkable transition from free-living species to parasitic species is very poorly understood, mainly because most of the evolutionary transitions to parasitism that have been characterized occurred tens or hundreds of millions of years ago.
This research addresses the origin of parasitism by utilizing a new model species that is in the early stages of becoming a parasite. As an adult, the lined sea anemone, Edwardsiella lineata looks and acts like a typical free-living sea anemone. However, its larva can invade the body of the comb jelly Mnemiopsis, where it develops into a small worm and makes its living by stealing partially digested food from the host's gut. Interestingly, in the absence of a suitable host, the anemone's larva can develop directly into an adult. This flexibility permits a direct comparison between the developmental pathway that leads from a larva to a parasitic worm and the developmental pathway that leads from a larva to a free-living sea anemone. Molecular and genomic techniques will be used to study the genes that control development, asking how the functions of these genes are altered during parasite development.
Aside from the fundamental scientific questions addressed by this research, there will be notable Broader Impacts. Given that the host species Mnemiopsis is a voracious predator on commercially important fishes, and Edwardsiella has the potential to control Mnemiopsis populations, greater knowledge of the parasite's development will inform its possible use as a biological control agent. Furthermore, this host-parasite system is easy to study in the classroom setting, and, as an outgrowth of the research, laboratory exercises will be developed that will allow high school and college biology instructors located along the New England coast to easily and inexpensively incorporate living demonstrations of parasitism into their lesson plans.
