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Joelle Kröll (Innsbruck University)

The two until now as subgernera adressed forms should be handled as two distinct species. The left, S. (pubescens subsp.) pubescens, occurs in the eastern Pyrenees, along the more or less continuous mountain range south and east of the Cerdanya/Cerdagne valley. The rightS. (pubescens subsp.) iratiana occurs on the highest summits and crests of the central and western Pyrenees. Photos: Pau Carnicero

Joelle Kröll's Master thesis was awarded with the Prize for the Best Plant Science Master Thesis, which was carried out at Innsbruck University in the year 2020.

Title: Allopolyploidy, introgression and morphological differentiation in the Pyrenean endemic Saxifraga pubescens of awarded thesis

Multiple data sources unravel inconspicuous diversity in a Pyrenean high mountain endemic: from one to two species, genome duplications and recurring hybridization

Hybridization is an important evolutionary force in plants, which can either lead to reduction of differentiation through introgressive hybridization or increase in diversity due to the appearance of a new evolutionary entity through hybrid speciation. For the latter to take place, hybrids need to overcome two major challenges, i.e. hybrid sterility and backcrossing with the parental lineages. One way to overcome both of these problems is allopolyploidy. Recurrent hybridization with co-occurring species has been reported in the Pyrenean endemic Saxifraga pubescens, but its evolutionary consequences as well as its link to polyploidy remain to date uncertain. Although two subspecies with allopatric distributions are recognised, i.e. S. pubescens subsp. pubescens and S. pubescens subsp. iratiana, some contradictory reports indicate overlapping distributions. Since the species is protected in some areas both in Spain and in France, it is necessary to clarify the intraspecific systematics of S. pubescens. For this purpose, we integrate morphological, relative genome size and molecular data from RADseq and plastid DNA sequencing to infer the evolutionary and biogeographical history of the species, with special focus on hybridization and polyploidy and to propose a congruent systematics framework. We observe both occasional occurrences of hybrids in populations of S. pubescens as well as entirely hybrid populations. Homoploid hybridization seems to generate the occasional hybrids, while the entirely hybrid populations consist of allopolyploids, which indicates fertility of the hybrids and their potential to create hybrid lineages (and eventually species). Morphology allows the proper identification of the two subspecies as well as the hybrids, with the exception of individuals with imbalanced introgression. In addition, the molecular data resolve both subspecies as monophyletic, but the species itself as polyphyletic and indicate that the two subspecies are consistently well-differentiated entities, and should be recognised as two separate species.

The Master thesis of Joelle Kröll was published (in : https://diglib.uibk.ac.at/ulbtirolhs/download/pdf/5341778?originalFilename=true


Joelle Kröll conducted this work at the Institute for Botany in the working group Evolutionary Systematics of Univ.-Prof. Mag. Dr. Peter Schönswetter and Ass. Dr. Pau Carnicero.