Extreme variation in flowering time between populations of Silene nutans

A large variation in flowering phenology has been observed among Danish pop ulations of Silene nutans. To test whether this variation is genetically de termined, we grew plants from 15 different Danish and one Swedish populatio n in a common garden experiment, and analysed their flowering time. The ext reme differences in onset of flowering observed in the field were maintaine d in the common garden. Most of the populations started within overlapping time periods, but two of them flowered much later, one of them at least one month later than the early populations. At this late time only a few flowe rs were left on plants from the other populations. Genetic differences in f lowering phenology were also found among offspring from crossings within an d between two populations from the same region. Genetic variation within th ese was relatively low, with estimated narrow sense heritabilities of 0.23 and 0.04, respectively. Differences in flowering time between populations w ere also to some extent co-dominantly inherited, although unexplained recip rocal differences complicated its interpretation. Our results, when compare d to others on isozyme divergence, suggest that unknown selective processes have affected the phenology of these populations.