Primary hybrid zone formation in Tephroseris helenitis (Asteraceae), following postglacial range expansion along the central Northern Alps

<p>Secondary vs. primary hybrid zone formation remains a challenging task as the time window in which these historical (vicariant) vs. contemporary (environmental-selective) processes are distinguishable may be relatively narrow.</p> <p>To examine the origin and structure of a transition zone between two subspecies of <i>Tephroseris helenitis</i> along the central Northern Alps, molecular (AFLP) and morphological (achene type) data as well as ecological niche models (ENMs) were used. Samples were collected over a <i>c.</i> 350 km-long transect, largely covered by ice during the Last Glacial Maximum (LGM).</p> <p>Genetically non-admixed individuals of subspp. <i>helenitis</i> vs. <i>salisburgensis</i> dominated the westernmost vs. eastern transect areas, with admixed individuals occurring in between. Cline for achene morphology was steep, largely non-coincidental, and displaced to the east of the cline centre for neutral AFLPs. During the LGM, ssp. <i>helenitis</i> should have been able to persist in a refugium southwest of the transect, while suitable habitat for ssp. <i>salisburgensis</i> was apparently absent at this time.</p> <p>Patterns of genetic and clinal variation in combination with our ENM data are suggestive of a primary hybrid zone that originated after the species' postglacial, eastward expansion.</p> <p> </p>