UC San Diego

Planarians and Hydra are famous for their incredible regenerative abilities and are considered classical organisms for studies in stem cell biology and regeneration. Besides these areas, both organisms have also emerged as popular models for evolution, aging and toxicology. In this thesis, I use a variety of quantitative methods to address three behavioral questions in these organisms; (1) how is planarian asexual reproductive behavior regulated, (2) what is the molecular mechanism controlling ethanol-induced behavior in planarians, and (3) what are the physical processes governing Hydra mouth opening. To answer the first question, we utilize the results of a long-term, large- scale experiment tracking tens-of-thousands of individual reproductive events to gain unprecedented insight into the life history strategies of three common planarian species : Schmidtea mediterranea, Dugesia japonica, and Dugesia tigrina. We find that, despite sharing a common anatomy and reproducing exclusively through binary fission, each species employs a distinct reproductive strategy on the population level. With regards to the second question, we develop quantitative methods to compare the behavioral responses of planarians exposed to exogenous ethanol and identify two genes that are necessary for a drunken behavioral response to acute ethanol exposure in planarians. Finally, we develop the first dynamical understanding of mouth opening in Hydra, a process which has been extensively studied physiologically and that requires tearing a new hole in the animals epithelium every time it wants to eat. Together, these studies demonstrate the power of quantitative methods to provide novel insights into diverse questions ranging from the population to the organismal tissue and molecular levels