Orbiliaceae

Orbiliaceae
Presumed Orbilia species growing on wet wood.
Scientific classification
Kingdom:	Fungi
Division:	Ascomycota
Subdivision:	Pezizomycotina
Class:	Orbiliomycetes
Order:	Orbiliales
Family:	Orbiliaceae Nannf.
Type genus
Orbilia Fr.
Genera
Arthrobotrys Brachyphoris Dactylella Dactylellina Dicranidion Duddingtonia Dwayaangam Gamsylella Hyalorbilia Monacrosporium Orbilia Pseudorbilia

A fungus of the genus Arthrobotrys, showing adhesive nets which it uses to trap nematodes.  Numbered ticks are 122 µm apart.

The Orbiliaceae are a family of saprobic sac fungi in the order Orbiliales. The family, first described by Nannfield in 1932, contains 288 species in 12 genera.^[1] Members of this family have a widespread distribution, but are more prevalent in temperate regions.^[2] Some species in the Orbiliaceae are carnivorous fungi, and have evolved a number of specialized mechanisms to trap nematodes.

Description

Orbiliaceae do not have stromata, dense structural tissue that produces fruit bodies. They have small disc-shaped apothecia, that are typically convex, brightly colored or translucent.^[2] Their ascospores are small (typically less than 10 x 1 µm), hyaline, and have an oval or ellipsoidal shape.^[3] Species are usually found in wood on both wet and dry habitats.^[2] Anamorph species are hyphomycetous.^[4]

Nematophagy

This family is well-known for its many nematophagous species.^[5] Shortly after coming into contact with its prey, fungal mycelia penetrate the nematode and spontaneously differentiate into functional structures, known as traps, which will ultimately digest the nematode's internal contents.^[6] There are 5 types of trap mechanisms recognized in this family^[6][7][8][9]:

• Adhesive network: the most common trap, formed by hyphal outgrowths that recurve into themselves to form nematode-trapping loops.
• Adhesive knob: a roughly spherical cell, attached to the hyphae either directly or on an erect stalk. Adhesive knobs are typically closely spaced along a section of hyphae.
• Nonconstricting rings: always found with the adhesive network traps, and formed from thickening hyphae that curve and fuse to the supporting stalk.
• Adhesive column: a layer of cells on a hyphae with an adhesive surface.
• Constricting rings: these are rings of hyphae that swell rapidly inwards upon contact with the nematode, quickly (in 1–2 seconds) "lassoing" the victim.

Genera

According to the most recent classification of Ascomycota^[10], the Orbiliaceae contain only two (teleomorph) genera, the Hyalorbilia and the Orbilia. Hyalorbilia is distinguished from Orbilia by having asci without a stalk that arise from croziers, a hemispherical to broadly conical, thin-walled apex, asci and paraphyses in a gelatinous matrix, and an ectal excipulum (the outer surface of a cup-like apothecium) of horizontal textura prismatica.^[11][12]

Anamorph genera of the Orbiliaceae include Anguillospora^[13], Arthrobotrys^[14], Dactylella^[15], Dactylellina, Dicranidion^[16], Drechslerella, Helicoön^[17], Monacrosporium, and Trinacrium. It has been suggested that the anamorph specialization illustrates convergent evolution occurring among mycelial fungi in aquatic and low-nitrogen habitats.^[18] This hypothesis has been borne out by recent phylogenetic and morphological studies.^[19]

In 2007, a new species was described from southwestern China with morphological features intermediate between Orbilia and Hyalorbilia. This species, named Pseudorbilia bipolaris Y. Zhang, Z.F. Yu, H.O. Baral & K.Q. Zhang, was placed into its own genus in the Orbiliaceae to accommodate its distinctive features.^[20]

References

1. ^ Kirk MP, Cannon PF, Minter DW, Stalpers JA. (2008). Dictionary of the Fungi. 10th edition. Wallingford: CABI. p. 485. ISBN 0-85199-826-7. 
2. ^ ^{a b c} Cannon PF, Kirk PM. (2007). Fungal Families of the World. Wallingford: CABI. p. 251. ISBN 0-85199-827-5. 
3. ^ Blackwell M, Alexopoulos CJ, Mims CW. (1996). Introductory Mycology. New York: Wiley. ISBN 0-471-52229-5. 
4. ^ Bisby, GR, Ainsworth GC, Kirk PM, Aptroot A. (2001). Ainsworth & Bisby's Dictionary of the Fungi / by P. M. Kirk... [et al.]; with the assistance of A. Aptroot... [et al.]. Oxon: CAB International. p. 369. ISBN 0-85199-377-X. 
5. ^ Pfister DH. (1997). Castor, pollux and life histories of fungi. Mycologia 89(1): 1-23.
6. ^ ^{a b} Barron, George L. (1977). The Nematode-destroying Fungi. Guelph: Canadian Biological Publications. ISBN 0-920370-00-4. 
7. ^ Yang Y, Yang E, An Z, Liu X. (2007). "Evolution of nematode-trapping cells of predatory fungi of the Orbiliaceae based on evidence from rRNA-encoding DNA and multiprotein sequences". Proc. Natl. Acad. Sci. U.S.A. 104 (20): 8379–84. doi:10.1073/pnas.0702770104. PMC 1895958. PMID 17494736. http://www.pnas.org/cgi/pmidlookup?view=long&pmid=17494736. "www.pnas.org". http://www.pnas.org/content/104/20/8379.full.pdf?ck=nck. Retrieved 2008-12-30. 
8. ^ Drechsler C. (1937). Mycologia 29: 447–552.
9. ^ Stirling GR. (1991). Biological control of plant parasitic nematodes. Wallingford, UK: C.A.B. International. ISBN 0-85198-703-6. 
10. ^ "Outline of Ascomycota - 2007". http://www.fieldmuseum.org/myconet/outline.asp#classTaph. Retrieved 2008-12-25. 
11. ^ Baral HO. (1994). Comments on “Outline of the ascomycetes – 1993”. Systema Ascomycetum 13: 113-128.
12. ^ Wu ML, Su YC, Baral HO, Liang SH. (2007). Two new species of Hyalorbilia from Taiwan. Fungal Diversity 25: 233–44.
13. ^ Webster J, Descals E. (1979). The teleomorphs of water-borne Hyphomycetes from fresh water. pp. 419–51. In: The Whole Fungus. Ed., Bryce Kendrick. National Museum of Natural Sciences, National Museums of Canada, Ottawa, Canada.
14. ^ Pfister DH. (1994). Orbiliafimicola, a nematophagous discomycete and its Arthrobotrys anamorph. Mycologia 86: 451–53.
15. ^ Thakur S, Zachariah K. 1989. Response of the fungus Dactylella rhopalota to bacteria. Plants & Soil 120: 87–93.
16. ^ Korf RP. (1992). A preliminary discomycete flora of Macronesia: Part 8, Orbiliaceae. Mycotaxon 45: 503–10.
17. ^ Pfister DH. (1995). Helicoon sessile, the anamorph of Orbilia luteorubella. Inoculum 46: 34 (Newsletter of Mycological Society of America).
18. ^ Moore D, Rayner ADM, Brasier CM. (1987). Evolutionary Biology of the Fungi: symposium of the British Mycological Society held at the University of Bristol, April 1986. Cambridge, UK: Cambridge University Press. pp. 191–201. ISBN 0-521-33050-5. 
19. ^ Li Y, Hyde KD, Jeewon R, Cai L, Vijaykrishna D, Zhang K. (2005). "Phylogenetics and evolution of nematode-trapping fungi (Orbiliales) estimated from nuclear and protein coding genes". Mycologia 97 (5): 1034–46. doi:10.3852/mycologia.97.5.1034. PMID 16596955. 
20. ^ Pseudorbilia gen. nov. (Orbiliaceae) from Yunnan, China. Fungal Diversity PDF

External links

• Orbilia at Index Fungorum
• Images of various Orbilia and Hyalorbilia species
• Videos of Arthrobotrys oligospora trapping nematodes