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CHAPTER 1
CHAPTER 2
CHAPTER 3
CHAPTER 4
CHAPTER 5
CHAPTER 6
CHAPTER 7
CHAPTER 8
CHAPTER 9
CHAPTER 10
CHAPTER 11
CHAPTER 12
CHAPTER 13
CHAPTER 14
CHAPTER 15
CHAPTER 16
CHAPTER 17
CHAPTER 18
CHAPTER 19
CHAPTER 20
CHAPTER 21

Form and function in the evolution of dermatophytes

Richard C. Summerbell

Mycology, Laboratories Branch, Ontario Ministry of Health, Toronto, Ontario, Canada
The phenotype of dermatophytes has been radically influenced by two very different evolutionary paths: that of the mostly sexual, soil-associated species, and that of the mostly asexual, non-soil-associated species. The former category, including geophiles and some zoophiles, is characterized by well established conidial dimorphism and the presence of apparent anti-arthropod-grazing structures such as helical appendages, as well as by growth factor independence, functional urease enzyme, and hair perforation organs. The latter category, including some zoophiles and all anthropophiles, is characterized by loss of some or all of the above characters. Phenotypic characters which are retained in the non-soil-associated dermatophytes, and likely selected for in their niche, include the production of infectious "substrate arthroconidia" and the production of secondary metabolites, often seen as coloured compounds in culture. The presence of xanthomegnin and other secondary metabolites, which have no known function in pathogenesis, may reflect deterrence of bacterial competitors in skin and nails. The diversity of such compounds may reflect "anomalizing selection" operational in the evolutionary maintenance of a general inhibition of unspecialized, opportunistic competitors. These competitors are non-specifically deterred by the saturation of the fungally colonized area with large quantities of metabolically inaccessible material, which must be maintained as inaccessible by evolutionarily accelerated but relatively undirected change.
 
 

PDF file

In: Kushwaha RKS, Guarro J (Eds.). Biology of Dermatophytes and other Keratinophilic Fungi.
Revista Iberoamericana de Micología, Bilbao, 2000.
 
 

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