Massive introgression weakens boundaries between a regionally endemic allopolyploid and a widespread congener

Abstract

Polyploidy is a significant driver of plant diversity and is, along with homoploid hybridisation, widely accepted as a common and important evolutionary force in plants. Here, we employed Amplified Fragment Length Polymorphism (AFLP) fingerprinting, ploidy level and genome size determination via flow cytometry and morphometry in order to disentangle origin and evolutionary history of tetraploid Knautia norica, endemic to the eastern Central Alps in Austria. Our data clearly support parapatric diploid K. carinthiaca, endemic to a single mountain slope, as one of the parental species. The AFLP data as well as morphological evidence suggest co-occurring and widespread diploid K. arvensis as second parent. Allopolyploidisation has thus obviously contributed to the greater evolutionary success of K. norica, compared with its stenoendemic progenitor K. carinthiaca. There is strong evidence for recent massive introgression of morphologically divergent K. drymeia into K. norica, which might present a threat to the long-term persistence of the latter species due to genetic erosion.