Evolution, taxonomy and ecology of the genus Thelebolus in Antarctica

An investigation of the biodiversity of some Antarctic lakes revealed that Thelebolus microsporus was one of the preponderant species. The genus Thelebolus is known to combine psychrophily with growth on dung and guano, suggesting that strains in lake biomats have originated from bird vectors. A natural association with skuas, petrels and other birds was confirmed by an analysis of bird cadavers, which showed frequent intestinal colonisation by T microsporus. Strains did not produce conidia but sporulated in vitro with ascomata on Carrot Agar (CA) at temperatures below 15 degrees C. The asci found were 8-spored and had forcible spore-discharge. Microsatellite data showed that several genotypes were recognisable, some of which had a very limited geographic distibution, suggesting the occurrence of local evolution in the Antarctic. Two undescribed species were encountered in lakes where birds are practically absent. These strains had reduced morphology, lacking forcible spore discharge, but produced conidia in abundance. The development of this morphology is probably attributed to a dramatic change in the life cycle due to the loss of the bird vector. Judging from beta-tubulin data, the species emerged 30-40 million years ago, when the Antarctic continent reached its current position. In an SSU rDNA tree of Thelebolus and purported relatives the genus was shown to have a distant position to remaining cup fungi. The maintenance of a separate order for Thelebolus and similar genera is therefore justified. The psychrotolerant genus Hyphozyma was found to be related, while Antarctomyces appeared closely similar to Thelebolus on the basis of rDNA ITS data; psychrophily apparently is a mainstay in the evolution of Thelebolus. About eighty strains and 181 herbarium collections of the genus Thelebolus, among which most of the ex-type cultures and type specimens, are studied for the morphology of the teleomorph and eventual anamorph. A key is provided for the morphological identification of the four species recognised. Polysporic strains are untited under the name T stercoreus. Thelebolus microsporus has a wide distribution in the Antarctic and elsewhere. Thelebolus globosus Brumm. & de Hoog and Thelebolus ellipsoideus Brumm. & de Hoog are newly described. Both are endemic to Antarctica. A hypothesis on the possible course of evolution in Antarctic Thelebolus is put forward.