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Evidence for post-mating species barriers in Ceratocystis

Markus Wilken: Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria

<div>Species of <em>Ceratocystis</em> (Microascales, Ascomycota) are all homothallic, but can outcross in artificial matings between self-sterile strains. Often, such laboratory crosses produce viable progeny, showing that the species are interfertile under artificial conditions. This sexual compatibility has been used to support the view that closely related species such as <em>C. eucalypticola</em>, <em>C. manginecans </em>and<em> C. fimbriata </em>represent host-specific strains of <em>C. fimbriata sensu stricto</em>, rather than discrete taxa. In this study, laboratory crosses were made between self-sterile isolates of <em>C. fimbriata</em> <em>sensu stricto</em>, <em>C. eucalypticola sensu stricto</em> and <em>C. manginecans sensu stricto</em> to consider whether post-zygotic barriers to sexual reproduction might be present. The mating tests produced normal ascomata from which ascospores could be recovered. Single ascospore progeny showed segregation of tested genetic markers, confirming the crosses represented true matings. However, analyses of the progeny showed they were the products of interspecific crosses, with reduced levels of fertility and non-random segregation of unlinked genetic markers. These characteristics are commonly associated with post-mating reproductive barriers found between two distinct taxa. The results provide evidence that sexual compatibility in laboratory tests can be misleading when invoking the biological species concept. Therefore, mating in culture including the production of viable progeny can fail to adequately consider potential post-reproductive barriers.</div>