Genetic diversity and structure of the endemic Tanacetum cinerariifolium as a consequence of multiple processes operating at different temporal scales

In this study on Dalmatian pyrethrum (Tanacetum cinerariifolium (Trevir.) Sch.Bip.), we combined genetic analysis and ecological niche modeling to investigate the intraspecific diversity, genetic structure, historical and contemporary distribution, and factors determining the observed diversification patterns of this endemic species from the eastern Adriatic coast. The study included 12 newly developed microsatellite markers that exhibited high polymorphism allowing the characterization of different populations. The level of genetic diversity (H_E) ranged from 0.399 to 0.616, with an average value of 0.534. Genetic differentiation (F_ST) between populations was 0.178. Most of the genetic diversity was attributed to differences among individuals within populations, but highly significant φ_ST values indicate the existence of genetic differentiation among populations. Bayesian analysis of population structure revealed the existence of two to four genetic clusters, and a correlation was found between environmental conditions and genetic clustering patterns, suggesting that local ecological conditions contributed to the emergence of distinct genetic patterns. The results of ecological niche modeling suggest that the Pleistocene climate has shaped the patterns of demographic history and diversification of this species in accordance with the refugia-within-refugia hypothesis. Understanding genetic diversity and structure provides important baseline information for the conservation of T. cinerariifolium genetic resources and for future breeding programs.