Geographical parthenogenesis, genome size variation and pollen production in the arctic-alpine species Hieracium alpinum

Abstract

Hieracium alpinum L. (Asteraceae) is an arctic-alpine species distributed throughout Europe with both diploid and triploid cytotypes. We determined the ploidy levels of plants from 23 populations from Austria, Bosnia and Herzegovina, Finland, Italy, Norway, Romania, Slovakia, Switzerland and Ukraine. Data showed a non-overlapping pattern of cytotype distribution: sexually reproducing diploids (2n = 2x = 18) occur solely in the Eastern and Southern Carpathians, while apomictic triploids (2n = 3x = 27) cover the rest of the range. Such clear-cut allopatry is rather rare in vascular plants with geographical parthenogenesis. Comparison of absolute genome size indicates genome downsizing (by on average 3.7%) of haploid DNA amount in triploids relative to diploids. Genome size further correlated with longitude and latitude in the Alps, with decreasing absolute DNA content from west to east, and from south to north. While previously published data indicated complete male sterility of triploid plants, we found that plants from the Alps and Bosnia and Herzegovina commonly produced some pollen, whereas populations from the Western Carpathians and Scandinavia seemed to be almost completely pollen sterile. Scenarios about the evolution of geographical parthenogenesis in H. alpinum are discussed.