Vectors, viscin, and Viscaceae: mistletoes as parasites, mutualists, and resources

Mistletoes are aerial, hemiparasitic plants found on trees throughout the world. They have unique ecological arrangements with the host plants they parasitize and the birds that disperse their seeds. Similar in many respects to vector-borne macroparasites, mistletoes are often detrimental to their hosts, and can even kill them. Coevolution has led to resistance mechanisms in hosts and specialization by mistletoes. Birds act as "disease vectors" for the mistletoe host in a mutualistic relationship. To disperse their seeds, mistletoes attract and manipulate their avian vectors in ways that are typical of both plants (offering a fruit reward) and parasites (changing vector behavior once they have been ingested). Mistletoes are important elements of the landscape that influence the spatial distribution of ecosystem resources. Their patchy distribution and complex interactions make their biology intriguing and their management and conservation challenging.