Ambrodiscus, a New Genus of Inoperculate Discomycetes from Ambrosia Beetle Galleries

AMBRODISCUS, A NEW GENUS OF INOPERCULATE DISCOMYCETES FROM AMBROSIA BEETLE GALLERIES

STEVEN E. CARPENTER Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331-2902

ABSTRACT The discomycete genus Ambrodiscus is described from Ambrosia beetle galleries in the sapwood of a recently fallen 130-year-old tree of Pseudotsuga menziesii. The features of this fungus are extremely reduced, apparently from adaptations to insect dispersal. The placement of A mbrodiscus in the Leotiales is discussed. Key Words: Ambrodiscus, Ambrosia fungi, fungus-insect interactions, Leotiales, wood decomposition.

Ambrodiscus Carpenter, gen. nov. Asci 8-spored, arising from croziers, J., cia. vate, 38-41 x 10-11 gm, the ascus apex broadly Apothecia sessilia, pulvinata, ad 0.5 mm diam, in rounded and lacking a pore, gradually labyrinthus insecti crescens. Texturae steriles demi- tapered to nutae, friablissimae. Asci octospori, clavati, pariete iodo a truncate base. tincto haud caerulescente, poro apicali nullo. Asco- Ascospores irregularly triseriate and biseriate sporae cylindracae, hyalinae, laeves. Vagina gelatinosa in the ascus, cylindrical with the ends rounded, ascosporas cingens. Species typica: Ambrodiscus pseu- 8-9 x 1.5-2.0 gm, aseptate, smooth, hyaline, dotsugae. with a single minute guttule at each end of the Apothecia sessile, pulvinate, less than 1 mm spore, the entire spore surrounded by a hyaline diam; asci 8-spored, clavate, lacking an apical gelatinous sheath, the sheath extending to ca 2.0 pore, J-; ascospores cylindrical, smooth, hyaline, gm from the spore wall. surrounded by a hyaline, gelatinous sheath; Paraphyses filamentous with rounded apices. growing in scolytid beetle galleries. smooth, hyaline, branched from the base, 1-2- Etymology: From a combination of the short- septate, ca 1.0 gm wide, equal to or slightly short- ened words ambrosia (ambro) and discomycete er than the asci. (discus). Habitat: Growing in the gallery of an unidentified ambrosia beetle, either Trypodendron lin- Ambrodiscus pseudotsugae Carpenter, sp. nov. eatum (01.), Gnathotrichus retusus (LeC.), or G. FIGS. 1, 2 sulcatus (LeC.), located in sapwood of a 1 -year fallen log of Pseudotsuga menziesii. Apothecia sessilia, pulvinata, superficialia, cir- HOLOTYPE: NORTH AMERICA. UNITED ca 350-400 gm diam, translucida, viridi-flava STATES. OREGON, Linn Co., Andrews Experi- pallida. Texturae steriles deminutae, friablissi- mental Forest, ca 80 km east of Eugene, 19.63 mae. Excipulum ectalum cellulis globosis, hy- km NE of Blue River, R5E, T15S, S14 NE, LTER alinis, parietibus tenuibus. Asci octospori, cla- Site #1, from an unidentified ambrosia beetle vati, 38-41 x 5-6 gm, pariete iodo tincto baud gallery in a Douglas-fir log, September 10, 1986, caerulescente, poro apicali nullo, apice late ro- S. E. Carpenter s.n., OSC #46720. tundatis, basin versus gradatim. Ascosporae cy- Etymology of the specific epithet: From Pseu- lindricae, hyalinae, laeves, aseptatae, 8-9 x 1.5- dotsuga menziesii, the species of tree in which 2.0 gm, extremis rotundatis. Vagina gelatinosa the fungus was discovered. ascosporas cingens. Holotypus: OSC #46720. Apothecia pulvinate, superficial, ca 350-400 DISCUSSION diam, translucent pale greenish-yellow. Ster- ile tissues reduced and extremely fragile. Outer Ambrodiscus was discovered in the examina- ectal excipulum of the apothecium composed of tion of a control treatment of a long term study cells which are globose, thin-walled and hyaline. of conifer log decomposition. In September. 1 98 5. 320 CARPENTER: AMBRODISCUS, GEN. Nov. 321

tto. Asci with ascospores. A. Asci showing internal arrangement of ascospores. B. Whole asci, mature iti) and immature (right). Holotype, crush-mount in cotton-blue lactic acid, x 2000.

over one hundred 130-year-old trees of Pseu- The apothecia of Ambrodiscus were found dotsuga menziesii were harvested and placed in growing on a dark brown microbial mat, which leiected sites in a 450-year-old Tsuga merten- was colonized by mites, nematodes, bacteria and _fla-Pseudotsuga menziesii forest in the Cas- fungi. Isolations made from galleries and the sur- 0de mountain range of Oregon. Temperatures rounding sapwood revealed that the fungal com- lthe study site range from a January mean of munity in which Ambrodiscus was found is .10 a July mean of 20 C. Annual precipitation composed mostly of species of Ophiostoma, WO es ca 250 cm. The logs were ca 50 cm in Trichoderma anamorphs of Hypocrea spp., the meter and at least 6 m long, with a sapwood r ca 3-4 cm thick. April, 1986, the sapwood of these logs was ed by the ambrosia beetles Trypodendron alum, Gnat hotrichus sulcatus and G. retusus. insects burrow through the relatively thick layer and into the sapwood of fallen trees, ling up to the heartwood. The galleries dug insects subsequently fill with a special- microbial community upon which the bee- graze and complete their life-cycle (Haanstad Norris 1985; Batra, 1963). The gallery which Wiled Ambrodiscus was vacant of ambrosia .:. Unfortunately, I do not know exactly species excavated the gallery, but the tun- )1I Which I found Ambrodiscus was made by FIG. 2. Ascospores. A. Clump of ascospores ad- hering by gelatinous sheathes. B. Single ascospore dem- Trypodendron hneatum, Gnat hotrichus onstrating polar guttule and gelatinous sheath. Holo- or G. retusus, the only three local species type, crush-mount in cotton-blue lactic acid. phase brosia beetle. contrast, x 2000. 322 MYCOLOGIA anamorphic form-genus Penicillium, and asco- I therefore hypothesize that mature asci mycetous yeasts. quesce or break open when an insect brusheses I found apothecia of Ambrodiscus in only one over the apothecium. The gelatinous insect gallery, although galleries from ten other around the ascospores may act in two or • MOM trees from the same experimental treatment were functions: 1) it may enable ascospores to examined. Whether Ambrodiscus itself is rare re- to scolytids crawling through the gallery,:. mains to be seen, for its frequency can only be tuating in their transport to a new scot determined from its successful culture followed lery; or 2) if the fungus is selectively graie-114- by an extensive survey for it in nature. animals inhabiting the galleries, then the heath The apothecia ofAmbrodiscus are so small that may serve as a protective layer, enablinli they are only observable with a high-powered spores to survive ingestion and subsequea dissecting microscope, and I also found them to persal in frass. The very small size and lack of be extremely fragile. Using a fine insect-mount- complex sterile tissue structures of the apoth • ing pin, I transferred apothecia to a drop of water indicate extensive adaptation to the insect gal. on a microscope slide and found that the weight lery. The environment of the gallery is very stable of a #1 glass coverslip placed on the drop com- and wet, with moisture content of surrounding pletely flattened the apothecia. I was thus unable sapwood reaching 100-150% of dry weight and to section it to determine the orientation of its sapwood temperatures reflecting only 50% of the excipulum. air temperature fluctuation (Mark Harmon, pers. I transferred whole apothecia of Ambrodiscus comm.). In the laboratory, I observed an insu. to Petri plates of malt extract agar (Anonymous, lating effect of sapwood: when it was chiseled 1968) amended with 100 ppm streptomycin-sul- open to reveal the galleries, the exposed fungi fate and incubated them at 15 C with fluorescent and gallery surfaces dried in just a few minutes lights set at a 12 hr diurnal cycle. The plates were under fiber-optic illumination. The apothecia of examined daily for two weeks, and yielded only A mbrodiscus have more hymenium volume than a contaminant species of Ophiostoma. I was un- that of sterile tissue: in the very moist environ- able to perform micromanipulation of asco- ment of the gallery, elaboration of sterile tissues spores for subsequent culture attempts. to protect the hymenium from desiccation tis- The ambrosia beetle galleries of the type in sues is probably unnecessary, and may have been which Ambrodiscus is found are convoluted and lost from ancestral morphology. This extreme narrow, with a diameter ranging from 1.68 mm adaptation to insect galleries indicates that the (Trypodendron lineatum) to 1.30 mm (Gnatho- teleomorphic state ofAmbrodiscus probably could trichus sulcatus) (Kinghorn, 1957). Because the not survive outside of a gallery or another equally galleries lie deep in the sapwood, dispersal of moist and stable environment. fungi specialized to this habitat is problematic. The morphology of Ambrodiscus is that of the As a consequence, the majority of fungi found order Leotiales sensu Carpenter (1988). Ambro- in those galleries, such as the anamorph and tel- discus may have evolved from a lignicolous sap- eomorph states of0phiostoma spp., have passive rophyte with functionally dispersive asci, alter- dispersal mechanisms specifically adapted to ing its apothecial form and ascus dehiscence vectoring by invertebrates. For example, almost mechanism as it adapted to insect dispersal: al- all of the fungi we have found in insect galleries ternatively, Ambrodiscus may have evolved from produce sexual and asexual fruiting structures some other group of ascomycetes, such as the which are are long and slender, and hold at their morphologically simpler Hemiascomycetes or the apex an orb of a mucoid, spore-filled liquid which closely related Pyrenomycetes. At present I be- easily adheres to the bodies of passing insects. lieve that its affinities are closest to the Leotiales. The spores are subsequently carried by those in- I contend that A mbrodiscus has undergone such sects to new logs (Batra, 1966, 1985). extensive adaptations to its specialized environ- The morphology of Ambrodiscus follows the ment that these adaptations have obscured its adaptive pattern of other insect-vectored fungi relationship with other genera in the Leotiales. of ambrosia beetle galleries. I have observed its The globose excipular cells suggest affinities with asci with phase-contrast microscopy and can de- the Dermateaceae, but similar excipular cells may tect no specialized apical dehiscence apparatus. also be found in genera of the Leotiaceae. I will CARPENTER: AMBRODISCUS, GEN. Nov. 323

-defer placement of this genus in any famil y until their dissemination by beetles. Trans. Kans. Acad. litore material can be found and for an analysis Sci. 66: 213-236. . 1966. Ambrosia fungi: Extent of specificity of its life-history. to Ambrosia beetles. Science 153: 193-195. . 1985. Ambrosia beetles and their associated ACKNOWLEDGMENTS fungi: research trends and techniques. Proc. Indian Acad. Sci. (Plant Sci.) 94: 137-148. I gratefully acknowledge funding for this study Carpenter, S. E. 1988. Leotiales, a name to replace grants from the National Science Foundation, Helotiales (Ascomycotina). Mycologia 80: (in tematic Biology program BSR-8500434 and press). Haanstad, stems program, BSR-8516590. J. 0., and D. M. Norris. 1985. Microbial symbiotes of the ambrosia beetle Xyloterinus po- litus. Microb. Ecol. 11: 267-276. LITERATURE CITED Kinghorn, J. M. 1957. Two practical methods of identifying types of ambrosia beetle damage. J. ous. 1968. Plant pathologists pocketbook. Econ. Entomol. 50: 213. 2r-ornmonw. Mycol. Inst., Kew. Lamport Gilbert, "Berkshire. 267 p. Accepted for publication November 6, 1987 L. R. 1963. Ecology of ambrosia fungi and

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