Ecological consequences of parasite host shifts under changing environments: More than a change of partner

Abstract

Parasitic plants, among many other parasitic organisms, are shifting in their geographic distribution in response to global change, establishing novel interactions with susceptible but previously unexposed host plants. Projections of future species assemblages in increasingly changing environments frequently overlook the strong capacity of these parasites to transform ecological systems, and host switching is considered a mere change of partner with no subsequent impact on ecosystem properties. We explore the ecological consequences of parasite host shifts analysing the growth and reproductive responses of two host trees that share a different interaction‐history with the parasitic plant Viscum album: recent in the case of Pinus sylvestris subsp. nevadensis and longstanding in that of Pinus nigra. We quantified growth by measuring primary (bud elongation) and secondary (dendrochronology) tree growth, and reproduction by quantifying cone crops, cone size, seed production, seed weight, seed germination, and emergence success. Pinus nigra registered a minor effect on reproduction but a major reduction in biomass, clearly reflected in lower primary and secondary tree growth, smaller cones and lighter seeds. On the contrary, P. sylvestris subsp. nevadensis underwent a strong decline of its reproductive capacity with no effects on growth, manifested in smaller cone crops, less seed production, and lower germination and emergence success. Synthesis. Mistletoe parasitism unleashes contrasting responses in taxonomically close host species with sharply different consequences for the forest ecosystem. While old hosts tolerate better the effect of parasitism, minimizing the impact on reproduction at the expense of their growth, recent hosts undergo greater effects of parasitism, suffering reproductive collapse with no perceptible loss of growth. We conclude that the increasing phenomenon of parasite host switching is not just a mere change of partner, but a driver of a new ecosystem organization. These results highlight the importance of considering the specific effects of newly established interactions when predicting future species assemblages, as these can trigger different ecological organizations from those we currently know.

Implications of mistletoe parasitism for the host metabolome: A new plant identity in the forest canopy

“…Interestingly, mistletoe acquires at least a part of these resources (Pate, True, & Kuo, 1991; Stewart & Press, 1990), derived from primary metabolism, directly from their host. At the same time, the host accumulates extra amounts of these compounds, benefitting mistletoe, by acquiring part of them (Pate et al, 1991; Stewart & Press, 1990), rather than the host itself, for instance, showing a reduction in host primary and secondary growth (Mellado & Zamora, 2020). In addition, mistletoes have high transpiration rates and low hydric potential (Ehleringer et al, 1985; Schulze & Ehleringer, 1984; Schulze, Turner, & Glatzel, 1984), guaranteeing the unidirectional flow from host to hemiparasite plant, especially for carbohydrates and amino acids (Glatzel & Geils, 2009; Lamont, 1983; López‐Sáez, Catalán, & Sáez, 2002).…”

“…concentrated in spring and autumn, hot and dry summers (June–September) and cold winters (December–March). This site is dominated by conifers (43%), especially P. nigra Arn., which is the main host and frequently parasitized by V. album (Mellado & Zamora, 2020). There are other species of pines, such as Aleppo ( Pinus halepensis Mill.…”

Freezing tolerance of seeds can explain differences in the distribution of two widespread mistletoe subspecies in Europe

“…Climate change and milder winters will probably affect the distribution of mistletoes in Europe. In montane pine forests of the Rhone valley (Switzerland) and Sierra de Baza (Spain), the occurrence of V. a. austriacum has already shifted northward in recent decades (Dobbertin et al, 2005;Zamora and Mellado, 2019;Mellado and Zamora 2020). We should expect similar latitudinal northward movement in the distribution of mistletoes elsewhere in…”

“…in Sierra de Cazorla. Mistletoe populations are patchily distributed in these mountains, being more frequent at intermediate altitudes, although they have recently expanded their distributional range to higher altitudes(Zamora and Mellado, 2019;Mellado and Zamora, 2020). Thesesites have a steep altitudinal gradient and have a typical continental Mediterranean climate with hot and dry summers (June-September), cool winters (December-March), and rainy autumns and springs.…”

GENETIC VARIATION OF TEAK MISTLETOE (Dendrophthoe pentandra (L.) MIQ.) BASED ON RANDOM AMPLIFIED POLYMORPHIC DNA (RAPD) MARKERS

“…The knowledge gained from research using Microsatellite markers was needed in designing conservation management programs for M. sylvaticum in the United Kingdom (Crichton et al 2012). Such information will also be useful for other related species of endangered non-weedy hemiparasites, according to Mellado & Zamora (2019), with similar traits and life history.…”