Abstract
Host specificity has been investigated for centuries in mistletoes, viruses, insects, parasitoids, lice and flukes, yet it is poorly understood. Reviewing the numerous studies on mistletoe host specificity may contribute to our understanding of these plants and put into context the dynamics at work in root parasitic plants and animal parasites. The mechanisms that determine host specificity in mistletoes are not as well documented and understood as those in other groups of parasites. To rectify this, we synthesized the available literature and analyzed data compiled from herbaria, published monographs and our own field studies in South Africa. As for other groups of parasites, multiple factors influence mistletoe host specificity. Initially, pollination affects gene flow. Subsequently, seed dispersal vectors (birds and marsupials), host abundance and compatibility (genetic, morphological, physiological and chemical), history and environmental conditions affect the interaction of mistletoes and their hosts and determine host specificity. Mistletoe-host network analyses and a geographic mosaic approach combined with long-term monitoring of reciprocal transplant experiments, genetic analyses of confined mistletoe populations and comparative phylogenetic studies could provide further insights to our understanding of host specificity. Some of these approaches have been used to study animal-plant interactions and could be adopted to test and evaluate host specificity in mistletoes at local and larger geographic scales.
Highlights
Parasitic plants are very diverse (3500–4000 species) and display a considerable variation in host-specificity (Norton and Carpenter 1998; Norton and de Lange 1999; Thorgood and Hiscock 2010)
Aerial parasitic plants—commonly called mistletoes, a term that describes a polyphyletic group of organisms with similar life histories—have received little research attention because they generally cause less damage to commercial plants compared to root parasites (Yoder 1999; Mathiasen et al 2008; Ntoukakis and Gimenze-Ibanez 2016)
We propose a geographic mosaic approach that may help to explain mistletoe host specificity and at the end we suggest this to be integrated with the current understanding of host specificity
Summary
Parasitic plants are very diverse (3500–4000 species) and display a considerable variation in host-specificity (Norton and Carpenter 1998; Norton and de Lange 1999; Thorgood and Hiscock 2010). To link mistletoe studies with root parasitic plants and animal host specificity, a comprehensive review of our current understanding of host specificity in mistletoes is required. Dispersal by animal vectors determines mistletoe– host interactions across time and space, which in turn influences the geographic mosaic of mistletoes and their hosts.
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