Dataset Information

Evidence for mycorrhizal races in a cheating orchid.

ABSTRACT: Disruptive selection on habitat or host-specificity has contributed to the diversification of several animal groups, especially plant-feeding insects. Photosynthetic plants typically associate with a broad range of mycorrhizal fungi, while non-photosynthetic plants that capture energy from mycorrhizal fungi ('mycoheterotrophs') are often specialized towards particular taxa. Sister myco-heterotroph species are often specialized towards different fungal taxa, suggesting rapid evolutionary shifts in specificity. Within-species variation in specificity has not been explored. Here, we tested whether genetic variation for mycorrhizal specificity occurs within the myco-heterotrophic orchid Corallorhiza maculata. Variation across three single-nucleotide polymorphisms revealed six multilocus genotypes across 122 orchids from 30 sites. These orchids were associated with 22 different fungal species distributed across the Russulaceae (ectomycorrhizal basidiomycetes) according to internal-transcribed-spacer sequence analysis. The fungi associated with four out of the six orchid genotypes fell predominantly within distinct subclades of the Russulaceae. This result was supported by Monte Carlo simulation and analyses of molecular variance of fungal sequence diversity. Different orchid genotypes were often found growing in close proximity, but maintained their distinct fungal associations. Similar patterns are characteristic of insect populations diversifying onto multiple hosts. We suggest that diversification and specialization of mycorrhizal associations have contributed to the rapid radiation of the Orchidaceae.

SUBMITTER: Taylor DL

PROVIDER: S-EPMC1691555 | biostudies-other | 2004 Jan

REPOSITORIES: biostudies-other

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Evidence for mycorrhizal races in a cheating orchid.

Taylor D Lee DL Bruns Thomas D TD Hodges Scott A SA

Proceedings. Biological sciences 20040101 1534

Disruptive selection on habitat or host-specificity has contributed to the diversification of several animal groups, especially plant-feeding insects. Photosynthetic plants typically associate with a broad range of mycorrhizal fungi, while non-photosynthetic plants that capture energy from mycorrhizal fungi ('mycoheterotrophs') are often specialized towards particular taxa. Sister myco-heterotroph species are often specialized towards different fungal taxa, suggesting rapid evolutionary shifts i ...[more]

PMID: 15002769

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Project description:Background and aimsMycorrhizal fungi are a critical component of the ecological niche of most plants and can potentially constrain their geographical range. Unlike other types of mycorrhizal fungi, the distributions of orchid mycorrhizal fungi (OMF) at large spatial scales are not well understood. Here, we investigate the distribution and diversity of Ceratobasidium OMF in orchids and soils across the Australian continent.MethodsWe sampled 217 Ceratobasidium isolates from 111 orchid species across southern Australia and combined these with 311 Ceratobasidium sequences from GenBank. To estimate the taxonomic diversity of Ceratobasidium associating with orchids, phylogenetic analysis of the ITS sequence locus was undertaken. Sequence data from the continent-wide Australian Microbiome Initiative were used to determine the geographical range of operational taxonomic units (OTUs) detected in orchids, with the distribution and climatic correlates of the two most frequently detected OTUs modelled using MaxEnt.Key resultsWe identified 23 Ceratobasidium OTUs associating with Australian orchids, primarily from the orchid genera Pterostylis, Prasophyllum, Rhizanthella and Sarcochilus. OTUs isolated from orchids were closely related to, but distinct from, known pathogenic fungi. Data from soils and orchids revealed that ten of these OTUs occur on both east and west sides of the continent, while 13 OTUs were recorded at three locations or fewer. MaxEnt models suggested that the distributions of two widespread OTUs are correlated with temperature and soil moisture of the wettest quarter and far exceeded the distributions of their host orchid species.ConclusionsCeratobasidium OMF with cross-continental distributions are common in Australian soils and frequently have geographical ranges that exceed that of their host orchid species, suggesting these fungi are not limiting the distributions of their host orchids at large spatial scales. Most OTUs were distributed within southern Australia, although several OTUs had distributions extending into central and northern parts of the continent, illustrating their tolerance of an extraordinarily wide range of environmental conditions.

Dataset Information

Evidence for mycorrhizal races in a cheating orchid.

Publications

Evidence for mycorrhizal races in a cheating orchid.

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