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Summary While angiosperm clocks can be described as an intricate network of interlocked transcriptional feedback loops, clocks of green algae have been modelled as a loop of only two genes. To investigate the transition from a simple clock in algae to a complex one in angiosperms, we performed an inventory of circadian clock genes in bryophytes and charophytes. Additionally, we performed functional characterization of putative core clock genes in the liverwort Marchantia polymorpha and the hornwort Anthoceros agrestis.Phylogenetic construction was combined with studies of spatiotemporal expression patterns and analysis of M. polymorpha clock gene mutants.Homologues to core clock genes identified in Arabidopsis were found not only in bryophytes but also in charophytes, albeit in fewer copies. Circadian rhythms were detected for most identified genes in M. polymorpha and A. agrestis, and mutant analysis supports a role for putative clock genes in M. polymorpha.Our data are in line with a recent hypothesis that adaptation to terrestrial life occurred earlier than previously expected in the evolutionary history of charophyte algae. Both gene duplication and acquisition of new genes was important in the evolution of the plant circadian clock, but gene loss has also contributed to shaping the clock of bryophytes.

Summary1 Islands representing four stage classes, dated by their height above sea level, in a Baltic land uplift area were used to study genet level dynamics during colonization of the clonal moss Hylocomium splendens . Allozyme electrophoresis involving 10 polymorphic loci enabled accurate identification of 103 haplotypes from a sample of 694 shoots collected along transects across 10 islands. 2 The populations consisted initially of scattered colonies with single clones. The number of clones, and the tendency of colonies to be multiclonal, increased significantly with increasing age of islands, whilst their mean size decreased significantly. In the Skeppsvik Archipelago, H. splendens thus shows repeated recruitment. 3 The percentage male or female fertile shoots relative to sterile shoots was positively correlated with age of the islands. The sex ratios were skewed during early colonization. 4 Spore capsules were found only in the oldest succession stage-classes. This can be explained by a greater chance for fertile males and females to grow within the fertilization range, which is limited to a few centimetres. 5 Genetic variation was accumulating with increasing population age. Correlations were stronger for mean number of alleles per locus ( A ) than for gene diversity ( H S ). 6 No isolation by distance was detected among populations, indicating efficient and essentially random gene flow, probably occurring via wind-dispersed spores.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Ecology.Summary 1 A study of allozyme variation in vegetatively propagating populations of the rhizomatous sedge Carex bigelowii, revealed high levels of clonal diversity (genet diversity) within populations. The structure of allelic variation within the populations suggests that sexual reprodugtion has played a significant role in these C. bigelowii populations, despite present lack of seedling recruitment. The study was carried out in moss-heath communities on Icelandic lava-fields. Two adjacent populations were studied at one site, while a third population was studied at a second site, 35 km away from the first two populations. 2 The number of genets detected in each population, among 85-88 analysed ramets, ranged from 41 to 55 (minimum estimate). Samples were taken every 4 m along transects in the populations. Ramets with the same allozyme genotype were often spatially aggregated. No seedlings have been observed in the populations during five years of demographic studies. 3 All the populations studied showed a diploid expression of allozymes and high levels of allelic variation, with on average 49% polymorphic loci (P), 1.77 alleles per locus (A) and an allelic diversity (Hs) of 0.167. Similar levels of within-population variability are found in many wind-pollinated and outcrossing plant species. 4 The difference between observed and expected heterozygosity was small in all populations, suggesting high levels of outbreeding. 5 Comparisons with other Carex taxa show that the levels of and structuring of allozyme diversity in C. bigelowii is similar to that in other outbreeding species (usually rhizomatous), and much higher than in inbreeding species (which are usually caespitose). 6 Only 5% of the total allelic diversity was explained by differences between the two study sites (GST = 0.055), suggesting extensive recent or historic gene-flow.

Among flowering plants, animals commonly act as pollinators. We showed that fertile moss shoots attract springtails and mites, which in turn carry moss sperm, thereby enhancing the fertilization process. Previously, fertilization of mosses was thought to depend on the capacity of individual sperm to swim through a continuous water layer. The role of microarthropods in moss fertilization resembles the role of animals as pollinators of flowering plants but may be evolutionarily much older because of the antiquity of the organism groups involved.