Parasitic plants: parallels and contrasts with herbivores

Abstract

Parasitic plants are common in natural communities, but are largely ignored in plant community theory. Interactions between parasitic plants and hosts often parallel those between herbivores and plants: both types of consumers display host preferences, reduce host biomass and alter host allocation patterns, modify plant community structure and dynamics, and mediate interactions between host plants and other organisms. In other cases, basic differences in mobility, hormonal and elemental composition and resource capture between plants and animals lead to different effects: parasitic plants have broad host ranges, affect and are affected by host plant physiology because of similar hormonal pathways between parasite and host, do not alter nutrient cycling as extensively as do herbivores, and may simultaneously parasitize and compete with hosts. Many fundamental aspects of the ecology of parasitic plants remain poorly studied, and research to date has been dominated by laboratory studies and studies of crop pests, rather than by studies of natural communities.

Successful translocation of the threatened New Zealand root-holoparasite Dactylanthus taylorii (Mystropetalaceae)

“…Assuming that such infections are in the minority and no other site-specific factors have influenced the outcome unduly, results indicate that the wide host range of dactylanthus (Ecroyd 1996;Moore 1940) does not translate to an equal preference for different hosts. This is in line with findings for other holoparasitic plants (Atsatt 1983;Gibson and Watkinson 1989;Marvier and Smith 1997;Press and Phoenix 2005) and would be a first step to identify principal and minor hosts of dactylanthus (Atsatt 1983;Pennings and Callaway 2002). Host preference may be due to both pre-infection and post-infection factors, where the former determines availability of suitable roots in space and time and the latter the physiological 'match' (Atsatt 1983;Press and Phoenix 2005) between host (species or individual) and parasite (Pennings and Callaway 2002;Watson 2009).…”

“…Á Mystropetalaceae Á Host preference Á Sowing method Á Dactylanthus taylorii Á New Zealand Introduction Despite a high percentage of rare or threatened species among holoparasitic angiosperms globally, little research has been undertaken on the establishment of populations (Marvier 1996), even though the need has been recognised. This seems due to the complication of having to consider both the species and their hosts in any management (Arunachalam et al 2004;Kuijt 1969;Marvier and Smith 1997) and because knowledge of basic aspects such as habitat and host requirements are not well understood for many of the holoparasitic families (Atsatt 1983;Bolin et al 2009;Musselman and Press 1995;Pennings and Callaway 2002) apart from agricultural crop-damaging taxa (Mescher et al 2009;Press and Graves 1995;Weber and Forstreuter 1987). While some generalisations will be justified, a focus on control and eradication of common weed species does usually not provide sufficient understanding of the life cycle and requirements of rare and threatened taxa (Atsatt 1983).…”

A holoparasitic plant severely reduces the vegetative and reproductive performance of its host plant in the Caatinga, a Brazilian seasonally dry forest

“…Resource acquisition by holoparasitic plants proceeds exclusively via haustoria, which drains water and metabolites from the bundles of the host plant (Pennings & Callaway 2002). In addition to photosynthate reallocation, holoparasitic plants may stimulate the secretion of hormones by the host plant, directly inoculating the host structures with their own hormones or mRNA (Knutson 1979;Ihl et al 1984;Westwood et al 2010).…”

“…Once parasitic plants have severely reduced host performance, parasitism may lead to changes in competitive interactions between host and non-host plants and impact the community structure, diversity, vegetation cycling and zonation (Pennings & Callaway 2002;Aukema 2003;Grewell 2008;Graffis & Kneitel 2015;Mourão et al 2016). These effects on community structure are often dynamic and may change depending on the performance of the parasite itself or due to environmental conditions (Pennings & Callaway 2002;Press & Phoenix 2005;Grewell 2008;Irving & Cameron 2009;Graffis & Kneitel 2015).…”

“…These effects on community structure are often dynamic and may change depending on the performance of the parasite itself or due to environmental conditions (Pennings & Callaway 2002;Press & Phoenix 2005;Grewell 2008;Irving & Cameron 2009;Graffis & Kneitel 2015). An aggressive parasite can drive a preferred host to local extinction, which may, in turn, result in the local extinction of the parasite (e.g.…”