Ecological niche differentiation between tetra- and octoploids of Jacobaea vulgaris.

Polyploid speciation is an ongoing, important source of angiosperm diversity. However, the ecogeographical differences between polyploids and their lower-ploid progenitors remain poorly understood. Here we explore patterns in the distributions of three Jacobaea vulgaris ploidy levels (4x, 6x and 8x) in Slovakia, which involved sampling at 203 sites and collecting information on the ploidy levels/chromosome numbers of 1023 individuals. For a subset of sites (171), we analysed the ecological differentiation between the two major ploidy levels, the tetra- and octoploids, which are recognized as separate subspecies, J. vulgaris subsp. vulgaris (2n = 4x = 40) and its autopolyploid derivative J. vulgaris subsp. pannonica (2n = 8x = 80). At most of the sites sampled (89.7%) only one ploidy level (subspecies) was recorded. Only 1.4% of the plants analysed were of the minority (6x) ploidy level and they occurred only together with plants of other ploidy level(s). The two major ploidy levels (subspecies) occurred in slightly different environments based on the 123 environmental variables studied. Separation of ploidy levels was mostly associated with type of habitat, habitat naturalness, geology, altitude, precipitation and temperature. In contrast to tetraploids, octoploids are restricted to warm and dry locations at low altitudes and in areas little affected by man. Despite the ecological niche separation between tetra- and octoploids along habitat and climatic gradients, and the more widespread distribution of tetraploids in the area studied, the ecological niche breadths of the two ploidy levels in Slovakia do not differ significantly.