Using genetic markers to investigate natural selection in fungal populations

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Abstract
Naturally occurring genetic markers can be exploited in a number of ways to measure natural selection in fungal populations. The potentials and pitfalls of these approaches are outlined. A review of existing experiments that have used genetic markers to estimate selection coefficients (s) in experimental and natural fungal populations indicates that differences in fitness between clones, populations, and subspecies may be substantial (mean s = 0.322), and that significant changes in the intensity and direction of selection may occur when environmental conditions alter. A reciprocal transplant experiment is described in which the relative selective values of three genetically marked populations of the canker pathogen Crumenulopsis sororia were compared under natural conditions. Large differences in selective value were found both among populations and within sites, but there was no evidence that genetic differentiation among populations was adaptive. The potential application of genetic markers for experimentally investigating mechanisms of speciation, adaptive genetic differentiation, and response to environmental change in fungi is discussed. Key words: genetic marker, natural selection, selection coefficient, Crumenulopsis sororia.