Genetically based population divergence of Silene latifolia from two climate regions

Background: Plants in hot and dry climates often flower earlier, make thicker leaves, and produce fewer flowers than conspecifics from relatively wet, cool climates. Silene latifolia, a dioecious, short-lived, flowering perennial, grows in both of these climates in Europe. Question: Is variation in traits seen among populations with divergent climates a result of genetic changes in response to local environmental conditions, differences in the degree of sexual dimorphism, or phenotypic plasticity? Hypothesis: Traits will differ between populations in a common garden as a result of genetic divergence, and exhibit a pattern of variation that is congruent with adaptation to climate. Methods: Morphological and phenological measurements were taken during two flowering seasons on plants growing in Croatia (relatively wet and cool) and Spain (hot and dry). Seeds from both regions were grown to flowering in the greenhouse and several traits were measured. Results: Significant divergence in traits existed between Croatia and Spain that persisted in the common garden (greenhouse), indicating that populations in these two regions likely represent different ecotypes. Plants from Spain flowered earlier in the field, made thicker leaves, and produced fewer flowers than plants from Croatia. Plants from Spain also showed greater sexual dimorphism than those from Croatia.