Growth, leaf freezing resistance and reproductive fitness differ between sexual diploid and apomictic tetraploid Ranunculus kuepferi plants along a climatic elevation transect and at natural growing sites

Apomictic plant taxa often show latitudinally and elevationally larger distribution ranges than their sexual relatives and tend to colonize previously glaciated areas more frequently. Despite numerous studies, the impact of the environment on this phenomenon is not fully understood. The present common-garden experiment on the alpine model plant Ranunculus kuepferi, with diploid sexual populations restricted to the south-western European Alps and tetraploid apomicts widespread throughout the Alpine Arc, should reveal how the cytotypes respond to the increasingly colder climate along a 1000 m elevation transect from the subalpine to the subnival zone in the Austrian Alps. Individuals originating from different populations in the European Alps were transplanted to plots at 4 elevations, and growth, leaf freezing resistance and reproductive fitness were recorded during the following 3 years. Additional measurements were carried out in natural populations. Diploids and tetraploids differed in their response to the respective site conditions along the elevation transect. Sexuals performed equal or even better than apomicts also at the highest site. Otherwise, tetraploids showed features, which could be advantageous in a cold climate: leaf mass per leaf area and rhizome mass increased with elevation, higher leaf freezing resistance, and larger diaspores prone to persist in seed banks. These traits, in combination with other factors, may have facilitated the postglacial establishment of tetraploids in higher regions of the Alps. The results suggest that both different responses to site conditions and different modes of reproduction may have led to the cytotype-specific geographical distribution patterns.