An AFLP clock for the absolute dating of shallow-time evolutionary history based on the intraspecific divergence of southwestern European alpine plant species

The dating of recent events in the history of organisms needs divergence rates based on molecular fingerprint markers. Here, we used amplified fragment length polymorphisms (AFLPs) of three distantly related alpine plant species co-occurring in the Spanish Sierra Nevada, the Pyrenees and the southwestern Alps/Massif Central to establish divergence rates. Within each of these species (Gentiana alpina, Kernera saxatilis and Silene rupestris), we found that the degree of AFLP divergence (D-N72) between mountain phylogroups was significantly correlated with their time of divergence (as inferred from palaeoclimatic/palynological data), indicating constant AFLP divergence rates. As these rates did not differ significantly among species, a regression analysis based on the pooled data was utilized to generate a general AFLP rate. The application of this latter rate to AFLP data from other herbaceous plant species (Minuartia biflora: Schonswetter et al. 2006; Nigella degenii: Comes et al. 2008) resulted in a plausible timing of the recolonization of the Svalbard Islands and the separation of populations from the Alps and Scandinavia (Minuartia), and of island population separation in the Aegean Archipelago (Nigella). Furthermore, the AFLP mutation rate obtained in our study is of the same magnitude as AFLP mutation rates published previously. The temporal limits of our AFLP rate, which is based on intraspecific vicariance events at shallow (i.e. late glacial/Early Holocene) time scales, remains to be tested.