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Spatial Genetic Structure within Populations of Sorbus torminalis (L.) Crantz: Comparative Analysis of the Self-incompatibility Locus and Nuclear Microsatellites
Distribution of genetic diversity among and within plant populations may depend on the mating system and the
mechanisms underlying the efficiency of pollen and seed dispersal. In self-incompatible species, negative frequency-
dependent selection acting on the self-incompatibility locus is expected to decrease intensity of spatial genetic
structure (SGS) and to reduce population differentiation. We investigated two populations (peripheral and more
central) of wild service tree (Sorbus torminalis (L.) Crantz), a self-incompatible, scattered tree species to test the
differences in population differentiation and spatial genetic structure assessed at the self-incompatibility locus and
neutral nuclear microsatellites. Although, both populations exhibited similar levels of genetic diversity regardless
of the marker type, significant differentiation was noticed. Differences between FST and RST suggested that in the
case of microsatellites both mutations and drift were responsible for the observed differentiation level, but in the
case of the S-RNase locus drift played a major role. Microsatellites indicated a similar and significant level of
spatial genetic structure in both populations; however, at the S-RNase locus significant spatial genetic structure
was found only in the fragmented population located at the north-eastern species range limits. Differences in SGS
between the populations detected at the self-incompatibility locus were attributed mainly to the differences in
fragmentation and population history