Chemical and genetic variability of Thymus algeriensis Boiss. et Reut. (Lamiaceae), a North African endemic species

Abstract

Genetic and essential oil variations from eight Tunisian natural populations of Thymus algeriensis Boiss. et Reut. (Synonym Thymus hirtus Willd. subsp. algeriensis Boiss. et Reut.), a North African endemic species, were assessed using 47 terpenoids and 154 RAPD markers amplified by seven selected primers. Populations were collected from different geographical regions belonging to the sub-humid, upper semi-arid, mean semi-arid, lower semi-arid and upper arid bioclimates. Essential oil composition varied among populations. Five chemotypes according to main compounds have been distinguished: caryophyllene oxide/1,8-cineole/α-pinene, 1,8-cineole/α-pinene, 1,8-cineole/α-pinene/camphor, linalool and thymol chemotypes. A high genetic diversity within population and high genetic differentiation among them, based on RAPDs, were revealed (Hpop=0.303 and GST=0.339) caused both by the habitat fragmentation, the low size of most populations and the low level of gene flow among them. The genetic and chemical structures are in accordance with geography distances indicating isolation by distance. The UPGMA dendrogram and PCA analysis based on volatiles yielded higher separation among populations indicated specific adaptation of populations to the local environments. While the results obtained through RAPDs separated populations into three distinct clusters each of them including populations closed to their geographical origin. Genetic and chemical data were correlated based on Mantel test. Population differentiation performed on the two sets of data was similar to that shown using RAPDs suggesting higher accuracy of these markers. Given the high differentiation among all populations, conservation strategies should take into account genetic diversity and chemical variation levels in relation to bioclimatic and geographic location of populations.