Kjell I. Flatberg

Glacial survival may matter after all: nunatak signatures in the rare European populations of two west‐arctic species

Biogeographers claimed for more than a century that arctic plants survived glaciations in ice‐free refugia within the limits of the North European ice sheets. Molecular studies have, however, provided overwhelming support for postglacial immigration into northern Europe, even from the west across the Atlantic. For the first time we can here present molecular evidence strongly favouring in situ glacial persistence of two species, the rare arctic‐alpine pioneer species Sagina caespitosa and Arenaria humifusa. Both belong to the ‘west‐arctic element’ of amphi‐Atlantic disjuncts, having their few and only European occurrences well within the limits of the last glaciation. Sequencing of non‐coding regions of chloroplast DNA revealed only limited variation. However, two very distinct and partly diverse genetic groups, one East and one West Atlantic, were detected in each species based on amplified fragment length polymorphisms (AFLPs), excluding postglacial dispersal from North America as explanation for their European occurrences. Patterns of genetic diversity and distinctiveness indicate that glacial populations existed in East Greenland and/or Svalbard (A. humifusa) and in southern Scandinavia (S. caespitosa). Despite their presumed lack of long‐distance dispersal adaptations, intermixed populations in several regions indicate postglacial contact zones. Both species are declining in Nordic countries, probably due to climate change‐induced habitat loss. Little or no current connectivity between their highly fragmented and partly distinct populations call for conservation of several populations in each geographic region.

Genetic variation in three Chinese peat mosses (Sphagnum) based on microsatellite markers, with primer information and analysis of ascertainment bias

Abstract Primer sequences are provided for amplification of 21 microsatellite-containing loci in Sphagnum. Although these primers were developed for species in Sphagnum section Subsecunda, they amplify microsatellite loci in most species that have been tested across the genus Sphagnum. Results are described from a survey of genetic variation in three species of Sphagnum collected in China: S. junghuhnianum in section Acutifolia, and S. palustre and S. imbricatum in section Sphagnum. Six and eight multilocus genotypes were detected within one population each of S. junghuhnianum and S. palustre, respectively. Four populations of S. imbricatum were sampled; they vary substantially in allele frequencies and in the amount of genetic diversity detected; overall, approximately 40% of the genetic variation sampled within S. imbricatum could be attributed to differentiation among populations. Microsatellite profiles indicate that S. palustre gametophytes are diploid whereas those of S. junghuhnianum and S. imbricatum are haploid.

Origin, taxonomy and population structure of the allopolyploid peat mossSphagnum majus

The polyploid peat mossSphagnum majus shows considerable phenotypic plasticity along ecological gradients in mires. It is considered taxonomically heterogeneous, and two subspecies have been described. Isozyme analyses were carried out on populations ofS. majus from Central Norway and from eastern coast of North America in order to assess the origin, taxonomy and population structure of this species. High levels of fixed heterozygosity in the populations demonstrate thatS. majus is a genetic allopolyploid. At all ‘loci’ screened, extant populations ofS. cuspidatum shared enzyme bands withS. majus. The other most likely progenitor based on morphology,S. annulatum, was fixed for enzyme bands not found inS. majus. The progenitor genotype ofS. annulatum may have been missed because of inadequate sampling or extinction. Alternatively, another extinct or undetected taxon may constitute the second progenitor. The observed patterns of genetic variation and linkage disequilibria were uncorrelated with the previously proposed subspecific classification ofS. majus. Lack of genetic divergence between continents suggests that the origins ofS. majus in Europe and North America were not independent. Low mutation rates and large effective population sizes may be important causing populations to diverge slowly, and may explain the observed patterns without hypothesising frequent long-distance dispersal.

The Narrow Endemic Sphagnum troendelagicum is an Allopolyploid Derivative of the Widespread S. balticum and S. tenellum

Abstract Sphagnum troendelagicum is only known from five localities in central Norway. Three populations were analyzed to assess its genetic affinities with other Sphagnum species. Isozyme and cytological data indicate that the species is allopolyploid. Morphological, RAPD, and isozyme data further indicate that it has originated from hybridization between Sphagnum tenellum (sect. Mollusca) and S. balticum (sect. Cuspidata). Sphagnum troendelagicum is morphologically distinct, with unique combinations of character states found in sect. Cuspidata and sect. Mollusca. Sphagnum tenellum is genetically similar to S. balticum, although these species are morphologically divergent. Our data support the inclusion of S. tenellum within sect. Cuspidata. Sphagnum troendelagicum appears to have originated recurrently; thus its restricted distribution cannot be ascribed to a single origin. The progenitor species are widespread in the Northern Hemisphere and often grow sympatrically in boreal areas. Hypotheses that may account for the restricted distribution of S. troendelagicum, including ecological tolerance of the allopolyploid and opportunities for hybridization between the progenitors, are discussed. Communicating Editor: Kathleen A. Kron

Genetic Variability in the Rare Norwegian Peat Moss Sphagnum troendelagicum

Abstract Three small populations of the rare allopolyploid peat moss species Sphagnum troendelagicum are studied using RAPD markers. Contrary to expectations, levels of neutral genotypic and haplotypic variation are moderately high in this seemingly asexual species. A model is presented for estimating relative impact of recombination on genetic variability. Recombinations appear to occur rarely in studied populations compared to mutation events, even though little significant linkage disequilibrium exists. We hypothesize that multiple origins of the species due to recurrent hybridization events may partially account for the observed variability.

Interploidal gene flow and introgression in bryophytes: Sphagnum girgensohnii × S. russowii, a case of spontaneous neotriploidy

Abstract Hybrid zones between female sporophyte-bearing haploid Sphagnum girgensohnii and male allodiploid S. russowii were studied. The existence of hybrids was initially hypothesized based on incidence of conspicuously large sporophytes in S. girgensohnii in the presence of male S. russowii. Measurements of nuclear DNA content, morphology and isozymes provide the first evidence of spontaneous hybridization across ploidal levels in bryophytes. Viable spores from the hybrid capsules yielded triploid protonemata and juvenile gametophores in culture. Isozyme profiles of the triploid gametophores displayed unbalanced heterozygous patterns containing two alleles. As S. russowii is an allodiploid species with S. girgensohnii and S. rubellum as progenitors, isozyme banding patterns of the triploids are interpreted as consisting of a single allele copy from the S. rubellum genome in S. russowii, and two copies of another allele at the same locus inherited from S. girgensohnii. The triploid sporophytes can be considered as F2 hybrids formed by introgression. The allotriploid gametophores are formed through diplospory or syndiploidy in the hybrid capsules. Comparison of hybrid sporophyte morphology to S. girgensohnii and S. russowii confirmed that hybrid capsules are larger and with an abnormally swollen sporophyte foot. The spore sizes of the hybrid capsules were significantly larger than spores from normal, intraspecific S. girgensohnii capsules. The percentage of germinated spores was <5% in cultures from hybrid sporophytes, which is much lower than in intraspecific sporophytes. The new knowledge opens the way for re-evaluation of polyploid evolution in bryophytes with emphasis on gametic non-reduction, introgression and two-step models of polyploid formation.

High genetic diversity in a remote island population system: sans sex

It has been proposed that long-distance dispersal of mosses to the Hawaiian Islands rarely occurs and that the Hawaiian population of the allopolyploid peat moss Sphagnum palustre probably resulted from a single dispersal event. Here, we used microsatellites to investigate whether the Hawaiian population of the dioicous S. palustre had a single founder and to compare its genetic diversity to that found in populations of S. palustre in other regions. The genetic diversity of the Hawaiian population is comparable to that of larger population systems. Several lines of evidence, including a lack of sporophytes and an apparently restricted natural distribution, suggest that sexual reproduction is absent in the Hawaiian plants. In addition, all samples of Hawaiian S. palustre share a genetic trait rare in other populations. Time to most recent ancestor (TMRCA) analysis indicates that the Hawaiian population was probably founded 49-51 kyr ago. It appears that all Hawaiian plants of S. palustre descend from a single founder via vegetative propagation. The long-term viability of this clonal population coupled with the development of significant genetic diversity suggests that vegetative propagation in a moss does not necessarily preclude evolutionary success in the long term.

Population Structure and Taxonomy of Sphagnum cuspidatum and S. viride

Abstract Based on morphology, Sphagnum cuspidatum and S. viride have been recognized as two different species. Morphs corresponding to the two taxa were investigated in nine populations situated in Norway, Denmark, Canada, and U.S.A. Eleven putative isozyme loci were used to map genetic variation and to assess the taxonomic relationships. Cluster analysis of allele frequency data did not produce groups corresponding either to the two species or to geographic regions. Low evolutionary rates because of low mutation rates and large effective population sizes may account for the lack of divergence between populations, even across continents. A test of population differentiation showed significant divergence between the two morphs in one population indicating that they might be reproductively isolated. However, in five other populations containing both morphs no such patterns were found suggesting that the speciation process is incomplete. A species level recognition of these taxa is not supported by isozyme data, rather taxonomic recognition at the subspecific level may be more appropriate. A population of S. trinitense expressed unique allele combinations, supporting the view that it is a distinct species different from S. cuspidatum.

Studies of fertility of Dicranum majus in two populations with contrasted sporophyte production

Abstract Some populations of the dioicous moss Dicranum majus Sm. in southern Norway do not or only rarely produce sporophytes, while most populations in central Norway produce sporophytes frequently. Two populations of D. majus in spruce forest, one from southern Norway (without sporophytes) and one from central Norway (with many sporophytes) were investigated to find differences in sexual reproduction between them. The population in southern Norway had only a few perichaetia and neither dwarf males nor sporophytes, while perichaetia, males and sporophytes were abundant in the population from central Norway. Shoots with dwarf males formed perichaetia more often than shoots without males, and the proportion of fertilized archegonia increased with increasing numbers of males on the shoots. Genetic differences or some earlier environmental ‘disaster’ related to extreme drought or heavy pollution loads are discussed as possible explanations for the sparse sporophyte production in southern Norway. In order for sporophytes to be produced in the population in southern Norway, new males must be established from spores from outside.

Species Delimitation and Relationships of the Sphagnum recurvum Complex (Bryophyta)-as Revealed by Isozyme and RAPD Markers

Isozyme data from 26 populations of six species within the Sphagnum recurvum complex, as well as from the two outgroups S. balticum and S. lindbergii, were used to infer the relationships of these populations, and to assess to what degree these relationships are reflected in alternative classifications. A subset of eight populations, comprising four species, were analyzed for both isozyme and RAPD markers. Population aggregation analysis, cluster analysis of pairwise distances and parsimony analysis of allele fre- quency data grouped populations with brown spores in three distinct clusters corresponding to S. angusti- folium, S. flexuosum and S. recurvum s. str., whereas no clusters corresponding to any of the yellow-spored taxa (S. brevifolium, S. fallax and S. isoviitae) could be discerned. Genetic data corroborates morphological evidence suggesting that species level recognition is not warranted for S. fallax and S. isoviitae, whereas the status of S. brevifolium remains more uncertain. S. lindbergii deviated strongly from the remaining material in terms of both isozymes and RAPDs supporting its status as outgroup. S. balticum showed close genetic affinity to the yellow-spored taxa, suggesting that the S. recurvum complex is not monophyletic. Isozyme and RAPD markers yielded similar clustering patterns.