The Ecology of Freshwater Planarians

Planarians are on the rise as a model system for regeneration and stem cell dynamics. Almost in parallel the interest in planarian field biology has declined. Besides representing an independent research discipline in its own right, understanding of the natural habitat is also directly relevant to optimizing culture conditions in the laboratory. Moreover, the current laboratory models are but few of hundreds of planarian species worldwide. Their adaptation to a wide range of ecological niches has resulted in a fascinating diversity of regenerative abilities, body size, reproduction strategies, and life expectancy, to name just a few. With the currently ongoing establishment of large planarian species collections, such phenotypic diversity becomes accessible to comparative mechanistic analysis in the laboratory. Overall, we hope that this chapter inspires an integral view of the planarian model system that not only includes the molecular and cellular processes under investigation but also the evolutionary forces that shaped them in the first place.