Habitat fragmentation is known to cause genetic differentiation between small populations of rare species and decrease genetic variation within such populations. However, common species with recently fragmented populations have rarely been studied in this context. We investigated genetic variation and its relationship to population size and geographical isolation of populations of the common plant species, Lychnis flos-cuculi L., in fragmented fen grasslands. We analysed 467 plants from 28 L. flos-cuculi populations of different sizes (60 000-54 000 flowering individuals) in northeastern Switzerland using seven polymorphic microsatellite loci. Genetic differentiation between populations is small (F(ST) = 0.022; amova; P < 0.001), suggesting that gene flow among populations is still high or that habitat fragmentation is too recent to result in pronounced differentiation. Observed heterozygosity (H(O) = 0.44) significantly deviates from Hardy-Weinberg equilibrium, and within-population inbreeding coefficient F(IS) is high (0.30-0.59), indicating a mixed mating breeding system with substantial inbreeding in L. flos-cuculi. Gene diversity is the only measure of genetic variation which decreased with decreasing population size (R = 0.42; P < 0.05). While our results do not indicate pronounced effects of habitat fragmentation on genetic variation in the still common L. flos-cuculi, the lower gene diversity of smaller populations suggests that the species is not entirely unaffected.

Summary 1.Habitat fragmentation and variation in habitat quality can both affect plant performance, but their effects have rarely been studied in combination. We thus examined plant performance in response to differences in habitat quality for a species subject to habitat fragmentation, the common but declining perennial herb Lychnis flos-cuculi. 2. We reciprocally transplanted plants between 15 fen grasslands in north-east Switzerland and recorded plant performance for 4 years. 3. Variation between the 15 target sites was the most important factor and affected all measures of plant performance in all years. This demonstrates the importance of plastic responses to habitat quality for plant performance. 4. Plants from smaller populations produced fewer rosettes than plants from larger populations in the first year of the replant-transplant experiment. 5. Plant performance decreased with increasing ecological difference between grassland of origin and target grassland, indicating adaptation to ecological conditions. In contrast, plant performance was not influenced by microsatellite distance and hardly by geographic distance between grassland of origin and target grassland. 6. Plants originating from larger populations were better able to cope with larger ecological differences between transplantation site and site of origin. 7. Synthesis : In addition to the direct effects of target grasslands, both habitat fragmentation, through reduced population size, and adaptation to habitats of different quality, contributed to the performance of L. flos-cuculi . This underlines that habitat fragmentation also affects species that are still common. Moreover, it suggests that restoration projects involving L. flos-cuculi should use plant material from large populations living in habitats similar to the restoration site. Finally, our results bring into question whether plants in small habitat remnants will be able to cope with future environmental change.

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Performance of Lychnis flos-cuculi from fragmented populations under experimental biotic interactions AbstractTo study genetic effects of habitat fragmentation on plant performance and plant response to biotic interactions, we performed a greenhouse study with plants from 27 populations of the common plant Lychnis flos-cuculi differing in size, isolation, and microsatellite heterozygosity. We germinated seeds of 449 plants and grew up to nine offspring per maternal plant in single pots assigned to a factorial competition-by-pathogen infection treatment. We applied competition by sowing seeds of the grass Anthoxanthum odoratum into half of the pots. Moreover, half of the plants were inoculated with infective sporidia of the anther smut Microbotryum violaceum. Significant variation among populations in most size measures indicated genetic differentiation between populations. Plants from smaller populations developed fewer flowers than plants from larger populations indicating a genetic Allee effect. A decrease in flower number was also observed for populations with decreased microsatellite heterozygosity, suggesting higher inbreeding depression. Competition and pathogen infection reduced plant size independently from one another and independent from the fragmentation of the habitats of plant origin. While pathogen infection increased the total number of flowers per plant, it decreased the number of uninfected flowers per plant. This study demonstrates that even common species are negatively affected by habitat fragmentation. At the same time, it suggests little effect of habitat fragmentation on plant response to experimental competition and pathogen infection. Abstract. To study genetic effects of habitat fragmentation on plant performance and plant response to biotic interactions, we performed a greenhouse study with plants from 27 populations of the common plant Lychnis flos-cuculi differing in size, isolation, and microsatellite heterozygosity. We germinated seeds of 449 plants and grew up to nine offspring per maternal plant in single pots assigned to a factorial competition-by-pathogen infection treatment. We applied competition by sowing seeds of the grass Anthoxanthum odoratum into half of the pots. Moreover, half of the plants were inoculated with infective sporidia of the anther smut Microbotryum violaceum. Significant variation among populations in most size measures indicated genetic differentiation between populations. Plants from smaller populations developed fewer flowers than plants from larger populations indicating a genetic Allee effect. A decrease in flower number was also observed for populations with decreased microsatellite heterozygosity, suggesting higher inbreeding depression. Competition and pathogen infection reduced plant size independently from one another and independent from the fragmentation of the habitats of plant origin. While pathogen infection increased the total number of flowers per plant, it decreased the number of uninfected flowers per plant. This study demonstrates that ...

We cloned microsatellite repeats from ragged robin Lychnis flos‐cuculi (Caryophyllaceae) and developed 20 primer pairs for microsatellite marker analysis. We used 18 individuals of a large Swiss population to screen microsatellites. Seven loci were polymorphic. Between seven and 11 alleles were found per locus and the observed heterozygosity was between 0.308 and 0.813. Observed heterozygote deficits were significant in five of the seven loci, in line with the mixed mating system of L. flos‐cuculi.