Population genetics of the aquatic fungus Tetracladium marchalianum over space and time.
Aquatic hyphomycete fungi are fundamental mediators of energy flow and nutrient spiraling in rivers. These microscopic fungi are primarily dispersed in river currents, undergo substantial annual fluctuations in abundance, and reproduce either predominantly or exclusively asexually. These aspects of aquatic hyphomycete biology are expected to influence levels and distributions of genetic diversity over both spatial and temporal scales. In this study, we investigated the spatiotemporal distribution of genotypic diversity in the representative aquatic hyphomycete Tetracladium marchalianum. We sampled populations of this fungus from seven sites, three sites each in two rivers in Illinois, USA, and one site in a Wisconsin river, USA, and repeatedly sampled one population over two years to track population genetic parameters through two seasonal cycles. The resulting fungal isolates (N = 391) were genotyped at eight polymorphic microsatellite loci. In spite of seasonal reductions in the abundance of this species, genotypic diversity was consistently very high and allele frequencies remarkably stable over time. Likewise, genotypic diversity was very high at all sites. Genetic differentiation was only observed between the most distant rivers (∼450 km). Clear evidence that T. marchalianum reproduces sexually in nature was not observed. Additionally, we used phylogenetic analysis of partial β-tubulin gene sequences to confirm that the fungal isolates studied here represent a single species. These results suggest that populations of T. marchalianum may be very large and highly connected at local scales. We speculate that large population sizes and colonization of alternate substrates in both terrestrial and aquatic environments may effectively buffer the aquatic populations from in-stream population fluctuations and facilitate stability in allele frequencies over time. These data also suggest that overland dispersal is more important for structuring populations of T. marchalianum over geographic scales than expected.
Department of Plant Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America. jennia@uoregon.edu
Jennifer L
JL
Anderson
Carol A
CA
Shearer
D005658:Fungi / Q000235:genetics* / Q000302:isolation & purification; D005787:Gene Frequency; D014644:Genetic Variation; D005828:Genetics, Population; D005838:Genotype; D007087:Illinois; D045483:Rivers / Q000382:microbiology*; D014871:Water Microbiology; D014922:Wisconsin
Mycopathologia. 1997;138(3):163-71
16283114
Mycologia. 2004 Jan-Feb;96(1):57-65
21148829
Proc Natl Acad Sci U S A. 1996 Jan 23;93(2):770-3
8570632
Plant Dis. 2002 Aug;86(8):827-832
30818634
Phytopathology. 2002 Jul;92(7):703-9
18943265
Appl Environ Microbiol. 2001 Nov;67(11):5063-8
11679327
Mol Phylogenet Evol. 2005 Apr;35(1):60-75
15737582
Fungal Genet Biol. 2003 Nov;40(2):115-25
14516764
Syst Biol. 2003 Oct;52(5):696-704
14530136
Mycol Res. 2003 Feb;107(Pt 2):169-82
12747328
Appl Environ Microbiol. 2008 Feb;74(4):1094-101
18083884
Oecologia. 1982 Jan;52(1):1-4
28310100
Genetics. 2003 Aug;164(4):1567-87
12930761
Evolution. 1999 Feb;53(1):11-21
28565180
New Phytol. 2002 Nov;156(2):313-320
33873278
Heredity (Edinb). 2001 Aug;87(Pt 2):243-53
11703516
Clin Microbiol Rev. 1999 Jan;12(1):126-46
9880478
Fungal Genet Biol. 2000 Oct;31(1):21-32
11118132
Trends Ecol Evol. 1996 Feb;11(2):46-52
21237760
Proc Biol Sci. 2001 Jul 7;268(1474):1387-94
11429139
Mol Ecol. 2004 Jun;13(6):1679-92
15140110
New Phytol. 2008;178(1):3-7
18315696
Annu Rev Phytopathol. 1996;34:457-77
15012552
Mycologia. 2005 Jan-Feb;97(1):45-9
16389955
Genetics. 2000 Jun;155(2):945-59
10835412
Evolution. 1984 Nov;38(6):1358-1370
28563791
Mol Ecol Notes. 2007 Jul 1;7(4):574-578
18784791
Mol Ecol. 2002 Nov;11(11):2229-39
12406235
Annu Rev Phytopathol. 1998;36:249-75
15012500
Environ Microbiol. 2005 Feb;7(2):270-80
15658994