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.

Filipendula vulgaris is a characteristic species of dry nonacidic grasslands in Denmark. This habitat type occurs only on marginal areas not suitable for agriculture or urbanization and that are by their nature fragmented. The population genetic structure of F. vulgaris was investigated in 17 populations within two regions of Denmark, using isozyme electrophoresis. Small populations were found to have significantly fewer polymorphic loci than larger populations, but all populations maintained the same common allelic variants. The degree of isolation of individual populations did not affect the amount of genetic variation. Offspring arrays revealed a very high outcrossing rate (0.96). The field study demonstrated a very high level of gene flow between populations considering that small insects are thought to be the main pollinators of this species. An experiment to verify whether pollen transport by wind could explain the results from the field study demonstrated long-distance transport from isolated plants to bagged plants. Filipendula vulgaris pollen grains are very small and this explains why outcrossed progeny were found using pollination bags with small pore sizes. We conclude that wind pollination is indeed possible and together with insect pollination is causing the observed patterns of genetic variation. The substantial gene flow between populations may be reducing the effects of genetic drift in the small fragmented populations of F. vulgaris.

Genetic variation encoded by five isozyme loci was investigated in 17 populations of Armeria maritima in Denmark. A. maritima maintains most of its isozymic variation within populations and it is concluded that gene dispersal within populations is relatively high since random union of gametes was found in all populations. From the level of differentiation between populations, an estimate of gene flow was obtained. This intermediate level of gene flow is not sufficient to keep the investigated populations together in geographical clusters, in spite of the fact that the species is very common and widespread, and that dispersal corridors, in the form of roadside verges, are abundant. A comparison of plant diameter, which is a measure of plant age, and individual heterozygosity revealed no correlation between these two variables. The size of populations was found to be significantly correlated with the level of isozymic variation, measured as He, mean number of alleles and number of polymorphic loci. In addition, the small populations showed a higher genetic differentiation (Fst= 0.30) than the larger populations (Fst= 0.17).

International audienc

An electrophoretic study of segregation of isocitrate dehydrogenase (IDH) was undertaken in polyploid white clover (Trifolium repem L.). The study aimed to test the conflicting theories on enzyme inheritance patterns in this species. A number of controlled selfings and reciprocal crosses were performed as well as a study of distribution of alleles in a natural Danish population of white clover. The result of the selfing experiment was that the chosen material is strongly self-incompatible, The offspring from the crosses showed that two isoloci were present and that the alleles in these segregate in a Mendelian fashion. Five different IDH-phenotypes, composed of two alleles, where found in the natural population. This contrasts with previous findings, for this and other allotetraploid species, of one variant and one invariant isolocus. Maximum likelihood analysis of the distribution of these phenotypes showed that the two alleles were equally common on an overall population basis. Each of these alleles were, however, most frequent in one of the isoloci. The findings reported here strongly support the theory that white clover is an allotetraploid, showing disomic inheritance.