The Biogeography of Ectomycorrhizal Fungi a History of Life in The

Chapter 19 The biogeography of ectomycorrhizal fungi – a history of life in the subterranean Kabir G Peay1 and P Brandon Matheny2 1 Department of Biology, Stanford University, California, USA 2 Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN, USA 19.1 Why study the The documentation of basic biogeographic biogeography of patterns is fundamental to understanding ectomycorrhizal fungi? any taxonomic group. Knowing the time or place that an organism first arose and diver The science of biogeography maps spatial sified provides a window into the ecological patterns of biological diversity as a means of and evolutionary processes shaping their understanding the evolutionary and ecolog diversity and tells us how they responded to ical processes that structure life on this past changes in the environment, or how planet (Lomolino et al., 2006). Understanding they might fare under new climates. Yet, for spatial patterns of biodiversity has given rise the organisms studied by microbiologists to some of the most important discoveries in (fungi, bacteria, viruses) and that constitute modern science. The unique composition of the majority of life on earth, basic details of flora and fauna in different parts of the biogeography remain poorly known, and world, coupled with the spatial and tempo are still a subject of debate. ral coincidence of allied species, led both Biogeography was one of the earliest Darwin and Wallace to the idea of evolution branches of plant and animal biology, but by natural selection (Darwin, 1859; Wallace, the development of microbial biogeography 1855). Similarly, Wegener’s theory of conti lagged, because the use of morphological nental drift was formulated in great part by systematics to differentiate microbes and the realization that the fossil record pro reconstruct their evolutionary histories was vided a window into the past arrangement a “fruitless search”, to quote Carl Woese of landmasses, precisely because of the (Woese, 1987). As a result of the paucity of s patially restricted nature of species distribu morphological characters, until very recently tions. Biogeography may not be a field many microbes were thought to lack distinct familiar to most lay people or most micro biogeographical patterns (Finlay, 2002; biologists, but it is a powerful window into Peay et al., 2010c), and the importance of life on this planet. these organisms to the diversity and function Molecular Mycorrhizal Symbiosis, First Edition. Edited by Francis Martin. © 2017 John Wiley & Sons, Inc. Published 2017 by John Wiley & Sons, Inc. 341 342 Molecular mycorrhizal symbiosis of earth systems was underappreciated 19.2 Ectomycorrhizal (Falkowski et al., 2008). The molecular revo biogeography in the lution in DNA sequencing (Horton and pre‐molecular era Bruns, 2001; Woese, 1987) has provided the tools necessary for accurate identification The limitation placed on organisms in their and mapping of microbial distributions, ability to disperse is, perhaps, the primary and is forcing reevaluation of microbial driver of biogeographic patterns. This limita biogeography. tion creates a historical tie between where a Ectomycorrhizal fungi (EMF) are obli species arises and its geographical distribu gate symbionts of dominant tree species in tion. Early biologists viewed fungi as organ both temperate and tropical biomes, and are isms with incredible dispersal potential an important part of the diversity of terres and cosmopolitan ranges. Wallace, Darwin, trial ecosystems. While ecological studies of Candolle, and von Humboldt, upon whose EMF have traditionally focused on local‐scale writings the field of biogeography developed, processes, understanding the large‐scale dis were focused primarily on the distributions tributional patterns of these organisms can of plants and animals and, where fungi shed light onto many key biological ques were noted, it was mostly to indicate their tions, such as the role of symbiosis in shaping uniqueness. species distributions, and how nutrient Candolle, an influential Swiss botanist, mutualisms are affected by climate and geol alluded to this in his observation that fungi ogy. Mushroom‐forming fungi are relatively would occur, “everywhere upon the earth rich in morphological features among … when the same circumstances propitious microbial groups. However, the study of their to their production occur” (de Candolle, biogeography has also progressed slowly. 1820). Similarly, the Reverend Miles Joseph In this chapter, we review the current Berkeley, one of the early founders of the state of EMF biogeography in light of new field of mycology, wrote in a letter to Charles data stemming from the use of DNA‐based Darwin, “that were not Fungi so much the molecular tools. We begin first with a look at creatures of peculiar atmospheric conditions, the pre‐molecular history of EMF biogeog there would seem to be no limit to the diffusion raphy, before turning to recent develop of their species” (Berkeley, 1863). ments. The remainder of the review moves While Darwin and Wallace could view from smaller to longer temporal scales, large‐scale distributional patterns of plants beginning with current species’ distribu and animals as a historical record of evolu tional patterns, and their effects on commu tion precisely because of their limited ability nity composition and diversity at large to move between regions, the presence of scales. From there, we take a phylogeo fungi seems to have been seen by contem graphic approach to examine the population porary biologists more as a reflection of the level processes that give rise to species distri “peculiar” environmental conditions in a butions over thousands of years, before particular place, rather than a record of finally turning to historical biogeography to evolutionary history. This perception was examine how the movement of continents perhaps self‐reinforcing; early fungal tax and long‐distance dispersal have shaped onomists arriving in North America expected modern distributions of EMF taxa. to find European species and, as a result, Chapter 19: The biogeography of ectomycorrhizal fungi – a history of life in the subterranean 343 (incorrectly) applied European names to the north from South American Nothofagaceae species they found – a problem that is still (southern beech) associates. In hindsight, being sorted out today. Consequently, however, none of these scenarios is likely m aking biogeographic conclusions from dis correct, as these investigators were misled at tribution records based on morphological a more fundamental level by the fact that taxonomy can be highly misleading (Pringle the key morphological feature distinguish and Vellinga, 2006). ing Rozites as a genus (presence of a mem The early view that fungi were “unrelia branous veil) evolved multiple times ble as biogeographic markers”, coupled with independently in the Cortinariaceae a paucity of reliable taxonomic data, slowed (Peintner et al., 2002). the development of fungal biogeography Even for more conspicuous taxa, basic (Pirozynski, 1983) for nearly a century. biogeographic patterns were difficult to dis However, improved fungal taxonomy and tinguish. For example, Watling proposed a increased global migration of European or boreal origin for boletes (Watling, 2001), North American trained systematists led to rather than an origin centered on their cur some attempts to assemble geographic dis rent day diversity in Southeast Asia (Corner, tribution information for fungi, and to 1972). While these hypotheses were not determine the extent to which factors such directly testable at the time, these early as climate or host identity affected these dis s cientists outlined the key questions that tributions (Bisby, 1943). Pirozynski (1983) continue to drive the field: was an early champion for the study of EMF (i) What are the centers of ectomycorrhizal as a window into biogeography, as he sus endemism? pected that their tight associations with host (ii) How important is long‐distance dispersal plants would more greatly limit their disper in shaping species distributions? sal and lead to distinct geographic pattern (iii) What are the key migration routes that ing, compared with other fungal groups. link regions? Still, he suspected much less endemism in (iv) When did this migration occur? fungi than in plants, at least in the context of These questions have proved fertile insular islands. grounds for the application of molecular Biogeographic hypotheses began to tools to assess biogeographic patterns among emerge, particularly for distinct groups with closely related species or populations (the clear centers of diversity. For example, the field of phylogeography), and more coarse strongly southern hemisphere‐biased distri global patterns at deeper taxonomic levels bution for the genus Rozites was thought to (the field of historical biogeography). suggest a Gondwanan origin (Bougher et al., 1994; Horak, 1981). However, distinguish ing amongst finer‐scale biogeographic sce 19.3 The advance narios was difficult. In examination of some of molecular phylogeography Central American Rozites, for example, Halling (Halling and Ovrebo, 1987) noted The development of DNA‐based tools for that it was not possible to tell if they were studying fungi has provided an unambigu northern co‐migrants with oaks from an ous way to discriminate fungal species Indo‐Malayan land bridge, or had migrated and reconstruct evolutionary relationships 344 Molecular mycorrhizal

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