Significant diversity and potential problems associated with inferring population structure within the Cenococcum geophilum species complex

Department of Plant Pathology and Microbiology, University of California, Riverside, California 92521, USA.
Mycologia (Impact Factor: 2.47). 11/2007; 99(6):812-9. DOI: 10.3852/mycologia.99.6.812
Source: PubMed


Cenococcum geophilum is perhaps the most widely distributed and most recognized ectomycorrhizal fungus with a host range of more than 200 tree species from 40 genera of both angiosperms and gymnosperms. We conducted a phylogenetic analysis on a large collection of isolates (n=74) from North America and Europe based on glyceraldehyde 3-phosphate dehydrogenase (gpd). A subset of isolates (n=22) also was analyzed with the more conservative LSU-rDNA locus. Significant nucleotide diversity was detected (approximately 20%) in the gpd region and the LSU-rDNA analysis supported that the C. geophilum isolates studied were monophyletic but distinct from two isolates, Am5-1 and N2-10, which previously were used in population genetic studies of this species. These results suggest that Am5-1 and N2-10 are likely two undescribed species or even genera. Our results suggest that C. geophilum sensu lato is a species complex and support previous molecular, physiological and morphological studies that have shown significant diversity in C. geophilum. This study also revealed that caution is advised when conducting population genetic studies in C. geophilum due to the possibility of pooling unrelated isolates. This potential problem also has implications for other fungal taxa because cryptic species routinely have been found in recent years based on molecular data.


Available from: Greg W Douhan
    • "The variation was positively and significantly correlated with physical distances, although involvement of some non-C. geophilum isolates may have influenced these results (Douhan, Huryn and Douhan 2007a). "
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    ABSTRACT: The asexual ectomycorrhizal fungus Cenococcum geophilum has a wide geographic range in diverse forest ecosystems. Although its genetic diversity has been documented at a stand or regional scale, knowledge of spatial genetic structure is limited. We studied the genetic diversity and spatial structure of C. geophilum in eight Japanese coastal pine forests with a maximum geographic range of 1364 km. A total of 225 samples were subjected to phylogenetic analysis based on the glyceraldehyde 3-phosphate dehydrogenase (GAPDH) gene followed by microsatellite analysis with five loci. The phylogenetic analysis based on GAPDH resolved three groups with most isolates falling into one dominant lineage. Microsatellite analyses generated 104 multilocus genotypes in the overall populations. We detected significant genetic variation within populations and genetic clusters indicating that high genetic diversity may be maintained by possible recombination processes at a stand scale. Although no spatial autocorrelation was detected at a stand scale, the relationship between genetic and geographical distances among the populations was significant, suggesting a pattern of isolation by distance. These results indicate that cryptic recombination events at a local scale and unknown migration events at both stand and regional scales influence spatial distribution and genetic structure of C. geophilum in coastal pine forests of Japan.
    FEMS Microbiology Ecology 09/2015; DOI:10.1093/femsec/fiv108 · 3.57 Impact Factor
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    • "Indeed, molecular phylogenetic analyses often challenge global and intercontinental fungal species (Douhan et al. 2011) and suggest that morphospecies often encompass cryptic biological species , which remain hidden because of the limited morphological characters available for fungi (Taylor et al. 2006; Jargeat et al. 2010). Although multigene phylogenies indirectly allow delineation of biological species by enforcing the Phylogenetic Species Concept (Taylor et al. 2000; Douhan et al. 2007), it is often difficult to settle a clear species boundary within quickly evolving species complexes. In such cases, population genetics approaches are powerful tools to reveal reproductive isolation and thus biological species. "
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    ABSTRACT: Biogeographical patterns and large-scale genetic structure have been little studied in ectomycorrhizal (EM) fungi, despite the ecological and economic importance of EM symbioses. We coupled population genetics and phylogenetic approaches to understand spatial structure in fungal populations on a continental scale. Using nine microsatellite markers, we characterized gene flow among 16 populations of the widespread EM basidiomycete Laccaria amethystina over Europe (i.e. over 2900 km). We also widened our scope to two additional populations from Japan (10(4) km away) and compared them with European populations through microsatellite markers and multilocus phylogenies, using three nuclear genes (NAR, G6PD and ribosomal DNA) and two mitochondrial ribosomal genes. European L. amethystina populations displayed limited differentiation (average F(ST) = 0.041) and very weak isolation by distance (IBD). This panmictic European pattern may result from effective aerial dispersal of spores, high genetic diversity in populations and mutualistic interactions with multiple hosts that all facilitate migration. The multilocus phylogeny based on nuclear genes confirmed that Japanese and European specimens were closely related but clustered on a geographical basis. By using microsatellite markers, we found that Japanese populations were strongly differentiated from the European populations (F(ST) = 0.416), more than expected by extrapolating the European pattern of IBD. Population structure analyses clearly separated the populations into two clusters, i.e. European and Japanese clusters. We discuss the possibility of IBD in a continuous population (considering some evidence for a ring species over the Northern Hemisphere) vs. an allopatric speciation over Eurasia, making L. amethystina a promising model of intercontinental species for future studies.
    Molecular Ecology 12/2011; 21(2):281-99. DOI:10.1111/j.1365-294X.2011.05392.x · 6.49 Impact Factor
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    • "Hence, the dominance of C. geophilum on Q. rubra in a novel habitat (see also Gebhardt et al. 2007) may be of ecological interest. Moreover, it has been also discovered that C. geophilum is a complex species (see Douhan et al. 2007). Thus, quantifying root tips typical of this EMF species based on its unique morphology may underestimate the actual number of EMF species. "
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    ABSTRACT: Non-native tree species have been widely planted or have become naturalized in most forested landscapes. It is not clear if native trees species collectively differ in ectomycorrhizal fungal (EMF) diversity and communities from that of non-native tree species. Alternatively, EMF species community similarity may be more determined by host plant phylogeny than by whether the plant is native or non-native. We examined these unknowns by comparing two genera, native and non-native Quercus robur and Quercus rubra and native and non-native Pinus sylvestris and Pinus nigra in a 35-year-old common garden in Poland. Using molecular and morphological approaches, we identified EMF species from ectomycorrhizal root tips and sporocarps collected in the monoculture tree plots. A total of 69 EMF species were found, with 38 species collected only as sporocarps, 18 only as ectomycorrhizas, and 13 both as ectomycorrhizas and sporocarps. The EMF species observed were all native and commonly associated with a Holarctic range in distribution. We found that native Q. robur had ca. 120% higher total EMF species richness than the non-native Q. rubra, while native P. sylvestris had ca. 25% lower total EMF species richness than non-native P. nigra. Thus, across genera, there was no evidence that native species have higher EMF species diversity than exotic species. In addition, we found a higher similarity in EMF communities between the two Pinus species than between the two Quercus species. These results support the naturalization of non-native trees by means of mutualistic associations with cosmopolitan and novel fungi.
    Mycorrhiza 05/2011; 22(2):121-34. DOI:10.1007/s00572-011-0387-x · 3.46 Impact Factor
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