Diploid chastity vs. polyploid promiscuity – Extensive gene flow among polyploid cytotypes blurs genetic, morphological and taxonomic boundaries among Dinaric taxa of Knautia (Caprifoliaceae)

Abstract

Heteroploid Knautia sect. Trichera constitutes a taxonomically intricate assemblage of taxa with highly complex genetic architecture, which is mirrored in high morphological variability and blurred boundaries among the species. Here, we aim to disentangle the relationships among the xerophytic taxa from the Dinaric Mountains on the western Balkan Peninsula, which, based on relative genome size estimations, comprise di-, tetra- and hexaploid populations. Our analyses of amplified fragment length polymorphisms (AFLP) revealed a clear genetic differentiation among the diploid members, which are also morphologically clearly divergent. On the other hand, the phylogenetic structure among tetraploid and hexaploid populations as well as the ties with their diploid progenitors are complex, conferring unclear boundaries among species. Tetraploids were intermingled among the divergent diploid lineages, suggesting recurrent polyploidisation and/or extensive gene flow across sympatric lineages, whereas hexaploids clustered in two groups, pointing to two separate origins. In line with the genetic pattern, there is a high overlap in morphological characters across and within different ploidies. Nevertheless, comparisons of environmental niches showed differentiation among the ploidy levels, with the niche of hexaploids being most divergent. It is thus obvious that dynamic polyploid evolution, virtual lack of crossing barriers among polyploid cytotypes pertaining to different species, and exceedingly variable morphology along with the uniformity of reproductive characters preclude establishing a clear-cut taxonomic structure. Still, albeit generally corroborating previous observations for K. sect. Trichera as a whole, our study restricted to a limited geographic and taxonomic assemblage yielded constructive insights towards a workable taxonomic framework in this complex system. As a result, we propose a revised taxonomic treatment, including description of a new species, Knautia ehrendorferi, but we are aware that species identifications will remain challenging also in the future. Data availabilityData will be made available on request.