Presentation on theme: "What is a fungal species?. Species Are species real? How do we define a species? Is there one “right” species concept that will be applicable to all organisms?"— Presentation transcript:
What is a fungal species?
Species Are species real? How do we define a species? Is there one “right” species concept that will be applicable to all organisms? What is the difference between a theoretical species concept and a operational species concept?
Species—Latin, kind A species is the principal unit of evolution (Ernst Mayr 1980) The lowest principal rank in the nomenclatural hierarchy (Dictionary of the Fungi)
Theoretical species concept Evolutionary Species Concept (Simpson 1951, 1961; Wiley 1978) —A single lineage of ancestor- descendent populations which maintains its identity from other such lineages and which has its own evolutionary tendencies and historical fate.
Operational Species Concepts Morphological Species Concept Biological Species Concept Phylogenetic Species Concept
Morphological Species Concept (MSC) Traditional approach in mycology—species are units that can be delimited on the basis of morphological characters, ideally by discontinuities in several such characters.
Example Ceuthospora lunata, a coelomycete causing black rot disease of cultivated cranberry in eastern North America “light” and “dark” strains recognized based on colony morphology Cranberry fruit inoculated with dark strain developed a uniform black rot, fruit inoculated with light strain developed a pale brown discoloration
Light strain conidia 6-11 x μm Dark strain conidia 7-15 x μm Strasseria geniculata – another fruit rot pathogen
Carris (1990) Can. J. Bot. 68: Light strain = Allantophomopsis cytisporea, originally described by Fries (1893) on Vaccinium vitis-idaea in Sweden Dark strain = Allantophomopsis lycopodina, originally described by von Höhnel (1909) on Lycopodium in Austria
Biological Species Concept (BSC) Species are groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups (Ernst Mayr 1942)
Tilletia L.-R. & C. Tulasne 1847 Type species: Tilletia caries (DC.) Tulasne based on 1815 specimen from Triticum aestivum (France) T. laevis Kühn (1873) based on 1872 specimen from wheat (Germany)
Short or dwarf bunt of wheat First published report from Montana in 1935: – Stunted plants – Spore balls (sori) hard, compact and round – Spores do not germinate under same conditions as T. caries and T. laevis – Soil infestation is the main source of infection; seed treatments ineffective
Common bunt teliospores Dwarf bunt teliospores
Tilletia contraversa Kühn (1874) Based on smut in ovaries of Elymus repens from Germany – Kühn compared quack grass smut with wheat bunt based on spore morphology and germination
Dwarf Bunt or TCK Smut – Reticulate teliospores with gelatinous sheath – Germination in 3-6+ wk at 3-8 C; requires light (T. caries & T. laevis germinate in <7 da at 15C without light) – Dwarf bunt infection occurs with deep, persistent snow cover – Dwarf bunt pathogen considered to have a wide host range including 45 grass species in 17 different genera
SpeciesSporesGermination# Sporidia T. cariesReticulate Exospore < 1 μm μm diam 1-2 wk at 15C light or dark 4-16 T. laevisSmooth μm diam 1-2 wk at 15C Light or dark 4-16 T. contraversaReticulate with gelatinous sheath up to 5 μm thick Exospore > 1 μm μm diam 3-10 wk at 5C Light required 14-30
The wheat bunt species are reproductively compatible Putative hybrids with spores exhibiting intermediate morphology found in natural populations Experimental hybrids generated by co- inoculation of wheat: – T. caries x T. contraversa – T. caries x T. laevis
Russell & Mills Electrophoretic karyotypes of Tilletia caries, T. controversa, and their F1 progeny: further evidence for conspecific status. MPMI 6:66-74
Questions 1.If T. caries, T. contraversa and T. laevis are reproductively compatible and produce viable progeny, should they be recognized as one, two, or three species? 2.Is additional evidence needed? If so, what type of evidence?
T. caries 4 T. caries J19 T. laevis T. laevis V766 T. contraversa WSP T. contraversa V528 T. contraversa T. laevis WSP T. trabutii V764 T. trabutii VPRI T. secalis WSP T. brevifaciens HUV T. brevifaciens V412 T. bromi ChInterc LC1328 T. bromi WSP T. bromi WSP T. bromi WSP T. vankyi WSP T. vankyi ChInterc LC1326 T. vankyi ChInterc LC1325 T. vankyi WSP T. vankyi FF7-8 T. laguri HUV T. lolii V767 T. goloskokovii WSP T. goloskokovii WSP T. goloskokovii WSP T. sphaerococca ChInterc LC1327 T. lolioli V763 T. fusca WSP T. elymi WSP T. togwateei WSP T. togwateei WSP changes Triticum spp. Secale cereale Thinopyrum intermedium Hordeum spp. Bromus spp. Lolium perenne Lolium rigidum Lagurus ovatus Apera interrupta Agrostis stolonifera Vulpia microstachys Poa reflexa Elymus glaucus Festuca rubra Loliolum subulatum MP analysis-- EF1A, ITS, RPB2 Germination at 5C
Pimentel et al Characterization of interspecific hybrids between Tilletia contraversa and T. bromi. Mycologia 92: Has reproductive compatibility been retained among host specific species of Tilletia? – T. bromi and T. contraversa are closely related species with overlapping host range; sympatric populations common in wheat fields in PNW
Pimentel et al Characterization of interspecific hybrids between Tilletia contraversa and T. bromi. Mycologia 92:
Questions 1.What can you conclude from the Pimentel et al study regarding reproductive compatibility of T. bromi, T. contraversa, and T. laevis? 2.Do the results of this study provide evidence for or against the conspecific status of the wheat bunt pathogens?
Phylogenetic Species Concept (PSC) A species is the smallest (exclusive) monophyletic group of common ancestry (de Queiroz & Donoghue 1988)
Example: Morchella Morchella –true morels – Black morels—M. elata group – Common morels—M. esculenta – Half-free morels—M. semilibera
Morchella elata group--Black Morel Morchella esculenta— Common or Yellow Morel Morchella esculenta courtesy of George Barron Morchella semilibera—Half-free morel
Verpa conica Verpa bohemica Mountain Blonde Morel—undescribed species
Summary 3 major clades corresponding to black morels (24 species), yellow morels (16 species), and M. rufobrunnea 37/41 spp with Laurasian distribution with 33 spp represented by multiple specimens exhibiting continental endemism: – 16/18 North American – 13/15 Eurasian
Limitations to MSC Fungi have a limited number of morphological traits, these traits can be highly plastic – Pleomorphy, dimorphism – Intraspecific morphological variability Morphological traits may evolve slowly and recently diverged species may not differ morphologically
Limitations to BSC 20% of fungi are asexual, others are homothallic or can’t be grown or crossed in artificial culture Interbreeding may be retained as an ancestral trait
Limitations to PSC Distinguishing populations from species-- where to draw the line Genealogies of different genes may give different species – Introgression, hybridization and horizontal gene transfer Recently diverged lineages may not show reciprocal monophyly
Genealogical Concordance Phylogenetic Species Recognition (GCPSR; Taylor et al 2000) Based on concordance of multiple gene genealogies: – Is the clade present in the majority of single-locus genealogies? – Is the clade well supported in at least one single- locus genealogy? – Is there support for the clade in the combined gene tree?
Fig. 3 from Taylor et al. 2000
Species concepts vs. speciation Species are separately evolving metapopulation lineages that acquire properties (reproductive isolation, ecological and phenotypic differences) at different time points during the course of divergence (de Queiroz 2007)
de Queiroz K PNAS 2005;102:
A unified species concept? “Lineages do not have to be phenetically distinguishable, diagnosable, monophyletic, intrinsically reproductively isolated, ecologically divergent, or anything else to be considered species. They only have to be evolving separately from other lineages.” (de Queiroz 2007)
Another unified species concept “A species is the smallest aggregation of populations with a common lineage that share unique, diagnosable phenotypic characters.” (Harrington & Rizzo 1999)
Consolidated Species Concept Extension of the “polyphasic” approach to fungal identification that weights MSC, ESC and PSC characteristics (Quaedvlieg et al Persoonia in press)