Effects of fragmentation phenomena on the genetic structure and gene flow in Centaurea cineraria group (Asteraceae) in the Mediterranean Basin

The complex history of the Mediterranean region illustrates how ancient and recent phenomena are closely associated with species distribution and the creation of phylogeographic divisions within Mediterranean flora. A good model to explore the genetic consequences of fragmentation can be found in Centaurea cineraria and its close relatives. We applied simple sequence repeat molecular markers to a dense population sampling throughout the distribution area of all C. cineraria taxa to study how fragmentation has altered the genetic structure and distribution of C. cineraria. The average gene diversity (H-e) was 0.286, and the average allelic richness (A(r)) was 3.65 and ranged from 2.15 (C. gymnocarpa) to 5.25 (C. busambarensis). The F-IS averaged a relatively high 0.223, ranging from -0.724 in C. aeolica subsp. aeolica to 0.589 in C. leucadea. Our results indicate that habitat fragmentation over several generations reduced heterozygosity due to random genetic drift in populations of C. cineraria. This heterozygosity erosion becomes more severe when the inbreeding coefficient is positive and the outcrossing rates show a significant increase. The results observed for outcrossing rates and inbreeding coefficient could also indirectly support the possibility of disrupted gene flow or mating pattern changes in fragmented C. cineraria populations.