Extreme variation in flowering time between populations of Silene nutans

A large variation in flowering phenology has been observed among Danish populations of Silene nutans. To test whether this variation is genetically determined, we grew plants from 15 different Danish and one Swedish population in a common garden experiment, and analysed their flowering time. The extreme differences in onset of flowering observed in the field were maintained 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 flowers were left on plants from the other populations. Genetic differences in flowering phenology were also found among offspring from crossings within and between two populations from the same region. Genetic variation within these was relatively low, with estimated narrow sense heritabilities of 0.23 and 0.04, respectively. Differences in flowering time between populations were also to some extent co-dominantly inherited, although unexplained reciprocal differences complicated its interpretation. Our results, when compared to others on isozyme divergence, suggest that unknown selective processes have affected the phenology of these populations.