Isolating mechanisms in fungi—prezygotic, postzygotic, and azygotic
Persoonia - Molecular Phylogeny and Evolution of Fungi , Volume 7 - Issue 2 p. 249- 260
What then are the biological processes that influence fungal speciation? Three aspects of fungal biology discussed herein deserved to be reemphasized. First, the great majority of fungi are haploid organisms. Secondly, fungi have expended a considerable amount of genetic energy to control the formation and maintenance of specific heterokaryons. Thirdly, the fungi taken as a group are paradoxical; against a background of extravagant and varied sexual cycles, fungi have a tendency to restrict gene flow and recombination. The prevalence of haploidy, the strict control of heterokaryosis, and an irregular but definite trend toward apomixis are attributes of fungal biology. These phenomena undoubtedly influence the operational details of fungal evolution and must be accommodated by any model which intends to explain the origin of fungal species. Virtually nothing is known about rates of evolution in fungal populations. However, at least three patterns are now evident among fungi with regard to their potential for change in gene frequency through time. The first pattern is that exhibited by imperfect fungi. Evolution in these fungi would be dependent largely upon mutation and selection with, at best, some parasexual activity but generally impaired gene flow. The second pattern is typified by Schizophyllum commune. This pattern includes sexuality; gene flow is continuous and controlled through homogenic incompatibility. The third pattern is recognized in Podospora anserina as well as in several basidiomycetes, Sistotrema brinkmannii, Mycocalia demdata, and Fomes pinicola. These species combine opposite effects for recombination, and gene flow within the species is discontinuous. Evolution in species of the third pattern should occur in quantum jumps rather than as a continuum. Sewall Wright (1931, 1932) in considering rates of evolution among populations has suggested that most rapid evolution might progress through subpopulations partially isolated which only occasionally or indirectly exchange genetic material. We simply do not now have sufficient data from fungal populations to integrate the fungi into such evolutionary theory.
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Lemke, P. A. (1973). Isolating mechanisms in fungi—prezygotic, postzygotic, and azygotic. Persoonia - Molecular Phylogeny and Evolution of Fungi, 7(2), 249–260.