Continent-wide distribution in mycorrhizal fungi: implications for the biogeography of specialized orchids

Abstract

The use of a widespread fungal OTU in P. deformis enables a broad distribution despite high mycorrhizal specificity. The Sebacina OTUs that are used by a range of Australian orchids occur on both sides of the continent, demonstrating that the short-range endemism prevalent in the orchids is not driven by fungal species with narrow distributions. Alternatively, a combination of specific edaphic requirements and a high incidence of pollination by sexual deception may explain biogeographic patterns in southern Australian orchids.

Geographical range and host breadth ofSebacinaorchid mycorrhizal fungi associating withCaladeniain south-western Australia

“…Further, Davis et al . () demonstrated that some of the fungi found associating with south‐western Australian orchids are also present in south‐eastern Australia, despite being separated by the arid Nullarbor Plain. As such, there is no evidence that the absence of suitable mycorrhizal fungi constrains the overall geographical range of orchid species associating with Sebacina in south‐western Australia.…”

“…For example, the closely related monotypic Pheladenia D.L.Jones & M.A.Clem. associates almost entirely with a single OTU of Sebacina across its broad geographical range (Davis et al, 2015). When taken together with the extensive sharing of fungal OTUs between Caladenia spp., these lines of evidence suggest that changes in mycorrhizal specificity is unlikely to have been the main driving mechanism in the diversification of some subgenera of Caladenia.…”

“…Further, at larger geographical scales (e.g. biogeographic regions), evidence suggests that the fungal species associating with orchids have wide distributions and broad habitat tolerances (Waterman et al, 2011;McCormick & Jacquemyn, 2014;Davis et al, 2015). However, data on most of these fungal species remain limited due to the reliance on molecular methods to detect them.…”

“…The recent proliferation of molecular studies of orchid mycorrhizal relationships has revealed that southern Australia is characterized by an unusually high incidence of specialized mycorrhizal associations relative to other orchid floras (Phillips et al, 2011a). There have been multiple evolutionary origins of mycorrhizal specialization in the Australian orchid flora, with highly specialized species already known from approximately seven orchid genera (Bougoure et al, 2009;Roche et al, 2010;Swarts et al, 2010;Wright et al, 2010;Otero et al, 2011;Phillips et al, 2011a;Linde et al, 2014;Davis et al, 2015). Southern Australia has a diverse, but highly threatened terrestrial orchid flora, with > 1000 species (Jones, 2006), over170 of which are currently federally listed as rare or threatened (Department of Environment, 2015).…”

Orchid diversity: Spatial and climatic patterns from herbarium records

“…For example, orchids rely on mycorrhizal fungi for nutrients, especially as seedlings (Rasmussen & Rasmussen, 2009). The degree of specialization in these orchid-mycorrhizae relationships varies, with implications for orchid distributions and rarity (Davis, Phillips, Wright, Linde, & Dixon, 2015;Jacquemyn, Brys, Waud, Busschaert, & Lievens, 2015). In turn, the distributions of mycorrhizal fungi depend largely upon edaphic conditions such as soil moisture, pH, nutrients, and organic content (McCormick & Jacquemyn, 2014;Nurfadilah, Swarts, Dixon, Lambers, & Merritt, 2013).…”