Polyploid evolution and Pleistocene glacial cycles: A case study from the alpine primrose Primula marginata...

Area of Science:

• Evolutionary Biology
• Plant Speciation
• Genomics

Background:

• Pleistocene climatic cycles influenced polyploid speciation and diversity reservoirs in Alpine refugia.
• The endemic hexaploid and dodecaploid cytotypes of Primula marginata lack ecological or morphological distinctions.
• Understanding the evolutionary history of P. marginata cytotypes is crucial for Alpine biodiversity research.

Purpose of the Study:

• To investigate the geographic distribution and variation of hexaploid and dodecaploid cytotypes in P. marginata.
• To infer the evolutionary history and determine the auto- vs. allopolyploid origin of dodecaploid populations.
• To elucidate the role of southern Alpine refugia in the speciation of P. marginata.

Main Methods:

• Flow cytometry was used to assess cytotype variation and distribution.
• Chloroplast (cp) and nuclear ribosomal (nr) DNA sequences (ITS region) were analyzed.
• Phylogenetic analyses of cpDNA and nrDNA were conducted to infer evolutionary relationships.

Main Results:

• Hexaploid cytotypes were found in the western range, and dodecaploids in the eastern range of P. marginata.
• Conflicting phylogenetic signals were observed between cpDNA (suggesting shared ancestry with P. latifolia) and nrDNA (implying common origins with P. allionii).
• Dodecaploid accessions exhibited higher ITS polymorphisms and nucleotide diversity than hexaploid accessions.

Conclusions:

• An initial chloroplast capture event likely occurred between ancestral P. latifolia and P. marginata lineages.
• Polyploidization between P. marginata-like and P. allionii-like lineages in a Maritime Alps refugium led to dodecaploid formation.
• The genetic data support an allopolyploid origin for the dodecaploid cytotypes of P. marginata.