Geographically structured host specificity is caused by the range expansions and host shifts of a symbiotic fungus

Abstract

The inability to associate with local species may constrain the spread of mutualists arriving to new habitats, but the fates of introduced, microbial mutualists are largely unknown. The deadly poisonous ectomycorrhizal fungus Amanita phalloides (the death cap) is native to Europe and introduced to the East and West Coasts of North America. By cataloging host associations across the two continents, we record dramatic changes in specificity among the three ranges. On the East Coast, where the fungus is restricted in its distribution, it associates almost exclusively with pines, which are rarely hosts of A. phalloides in its native range. In California, where the fungus is widespread and locally abundant, it associates almost exclusively with oaks, mirroring the host associations observed in Europe. The most common host of the death cap in California is the endemic coast live oak (Quercus agrifolia), and the current distribution of A. phalloides appears constrained within the distribution of Q. agrifolia. In California, host shifts to native plants are also associated with a near doubling in the resources allocated to sexual reproduction and a prolonged fruiting period; mushrooms are twice as large as they are elsewhere and mushrooms are found throughout the year. Host and niche shifts are likely to shape the continuing range expansion of A. phalloides and other ectomycorrhizal fungi introduced across the world.

The mid-domain effect in ectomycorrhizal fungi: range overlap along an elevation gradient on Mount Fuji, Japan

“…These results may indicate that many EM fungi have evolved compatibility to a wide range of co-occurring host lineages, such as Pinaceae, Fagaceae and Betulaceae that share overlapping geographic ranges (Bahram et al, 2013). Several studies also have suggested that host shifts among EM fungi prevail when preferable hosts are absent within a community (Trocha et al, 2012;Wolfe and Pringle, 2012;Bahram et al, 2013;Murata et al, 2013).…”

Trait‐dependent distributional shifts in fruiting of common British fungi

“…Changes in spatial distributions of ECM fungi could be constrained, if there is a level of specificity between fungus and host and/or if the distribution of the host is limiting (Vellinga et al 2009). Meanwhile, there is evidence that some ECM species can associate with novel hosts, facilitating range expansion and invasion into new habitats (Wolfe and Pringle 2012). Meanwhile, there is evidence that some ECM species can associate with novel hosts, facilitating range expansion and invasion into new habitats (Wolfe and Pringle 2012).…”

“…Saprotrophs may also be constrained by host distributions (Heilmann-Clausen et al 2016). Meanwhile, there is evidence that some ECM species can associate with novel hosts, facilitating range expansion and invasion into new habitats (Wolfe and Pringle 2012). Range expansions may lead on to fungal species becoming invasive (Kauserud et al 2007, Gladieux et al 2015.…”

Comparison of phylogeographical structures of a lichen‐forming fungus and its green algal photobiont in western North America

“…However, if the two taxa specialized on local genetic strains, then we would find some degree of congruence among clades even at neutral loci. The incongruence indicates a lack of discrimination by the fungus for specific genetic strains of the photobiont as long as it is the right species, which would allow the lichen to associate with a locally adapted photobiont genetic strain and thus persist even when the fungus disperses to new environmental conditions (Romeike et al ., ; Piercey‐Normore, ; Wolfe & Pringle, ; Werth & Sork, ). Across environments, it would be beneficial to switch to a different genotype of alga (Piercey‐Normore, ).…”

“…Across environments, it would be beneficial to switch to a different genotype of alga (Piercey-Normore, 2006). Thus, these non-specific associations among haplotypes may promote novel combinations of fungi and algae and create the opportunity for adaptation to new conditions (Wornik & Grube, 2010;Wolfe & Pringle, 2011). Following the initial contacts and establishment, site-specific selective forces would retain the successful thalli and remove unfit symbiotic combinations (Yahr et al, 2006).…”