Multiple, polytopic replacement of diploids by tetraploids in the Patagonian and Subantarctic plant Hypochaeris incana (Asteraceae, Cichorieae) as an adaptive response to post-glacial aridification?.

K. TREMETSBERGER; E. URTUBEY; A. TERRAB; C. M. BAEZA; M. A. ORTIZ; M. TALAVERA; C. KONIG; TEMSCH; S. TALAVERA; T. F. STUESSY

Fribourg

Simposio; Symposium Polyploidization, plant fitness and trophic interactions. University of Fribourg Switzerland.; 2009

University of Fribourg Switzerland.

   We ask how tetraploids are distributed in relation to diploids in the Patagonian and Subantarctic plant Hypochaeris incana endemic to southeastern South America and how polyploids have spread and expanded their range in relation to the diploids. We applied AFLP and chloroplast DNA (cpDNA) analysis to 28 resp. 32 populations throughout the distributional range of H. incana and assessed ploidy levels using flow cytometry. While cpDNA data suggest repeated or simultaneous parallel colonization of Patagonia and Tierra del Fuego by several haplotypes and/or hybridization, AFLPs reveal three clusters corresponding to geographic regions. The central and northern Patagonian clusters (~38-51° S), which are closer to the outgroup, contain mainly tetraploid, isolated and highly differentiated populations with low genetic diversity. To the contrary, the southern Patagonian and Fuegian cluster (~51-55° S) contains mainly diploid populations with high genetic diversity and connected by high levels of gene flow. The data suggest that H. incana originated at the diploid level in central or northern Patagonia, from where it migrated south. All three areas, northern, central and southern, have similar levels of rare and private AFLP bands, suggesting that all three served as refugia for H. incana during glacial times. In southern Patagonia and Tierra del Fuego, the mainly diploid populations seem to have expanded their population system in post-glacial times, when the climate became warmer and more humid. In central and northern Patagonia, the populations seem to have become restricted to favourable sites with increasing temperature and decreasing moisture. For this region, we infer a multiple, polytopic replacement of diploids by tetraploids, i.e., a parallel replacement in local populations, thus challenging the traditional view that polyploids spread by extending the range of their diploid progenitors. The most common mechanism of polyploid evolution is via unreduced gamete formation, which can be affected by environmental conditions. Our results allow us to hypothesize that polyploidization in H. incana occurred as an adaptive response to postglacial climate warming and aridification in Patagonia. This hypothesis needs to be tested via explicit assessment of cytotype fitness in different environments.....ver PDF