On the origins of parasite-extended phenotypes

Abstract

Parasites that adaptively manipulate the behavior of their host are among the most exciting adaptations that we can find in nature. The behavior of the host can become an extended phenotype of the parasites within animals such that the success and failure of the parasite's genome rely on precise change of the host's behavior. Evolutionary biology was borne from the close attention of naturalists such as Wallace and Darwin to phenotypic variation in seeking to understand the origins of new species. In this essay, I argue that we also need to think about the origins of parasite-extended phenotypes. This is a more difficult task than understanding the evolution of textbook examples of novelty such as the eyes of vertebrates or the hooves of horses. However, new tools such as phylogenomics provide an important opportunity to make significant progress in understanding the extended phenotypes of parasites. Knowing the origins of parasite-extended phenotypes is important as a goal all by itself. But the knowledge gained will also help us understand why complex manipulation is so rare and to identify the evolutionary tipping points driving its appearance.