Epi‐parasitic mistletoes don't parasitise their host's host and this supports the immunity hypothesis for host choice

Abstract

AbstractMistletoes have much higher transpiration rates than their hosts. This is the basis for the ecological “compatibility hypothesis” for host choice. The inability of mistletoes to penetrate a host and connect to its vascular system is the competing “immunity hypothesis”. Epi‐parasites would have to transpire faster than their host mistletoe, which must transpire faster than its host. Therefore, epi‐parasites should be able to parasitise their host's host. I surveyed epi‐parasite host choice at a site and found this did not happen. Globally about a quarter of all epi‐parasites are obligate. This supports the immunity hypothesis.