Genetic distances and phylogeography of selected disjunct moss populations in Europe

Abstract

Disjunct ranges are a common phenomenon in bryophytes. To test, whether these disjunctions are the result of the former continuous ranges (and therefore relicts) or the result of long-distance dispersal (and therefore result of spreading), five moss species were chosen for a case study: Campylopus oerstedianus, Hilpertia velenovskyi, Isothecium holtii, Rhytidium rugosum and Dichelyma capillaceum.<br /> Also, the problem of genetic diversity in space and time within the species morphologically not very variable has been studied. <br /> For the determination of genetic distances between the populations, the variation of the nuclear ribosomal non coding DNA region of the Internal Transcribed Spacer (ITS) and the trnL-F region of the chloroplast DNA was used. <br /> Campylopus oerstedianus has a scattered circum tethyan distribution ranging from Costa Rica to Georgia, the Pyrenees, the southern Alps and northern Greece. It is worldwide sterile and can propagate only vegetatively. In addition it is found in the Massif Central and the Vosges, in France. The molecular results showed that the populations in the Pyrenees, southern Alps and Greece have no genetic exchange and are possibly separated for long time. The disjunct populations in France are clustering with the population in the Pyrenees and are therefore possibly derived from the latter. The Greek population is highly isolated and genetically unrelated to the other European populations of C. oerstedianus, which counts for a very long isolation. <br /> Hilpertia velenovskyi is mainly a species of cold loess steppes in inner Asia. It is also found in Europe on loess cliffs from southern Poland to northern Serbia. It was recently discovered in Germany (Saxony and Rhinehessia). The molecular tree shows that Saxonian population is related to the Czech and both cluster with all other European populations except that from Rhinehessia. The latter is totally isolated also from a Chinese one which means that it has spread from somewhere else, probably from some populations which were not included in the study, or it has to be interpreted as an result of long lasting isolation since the last Ice Age. The continuity of the habitat (loess cliff), however, support this hypothesis. It would be the first molecular proof of a glacial relict among bryophytes.<br /> Isothecium holtii has been regarded either as good species, dubious species, or as a variety of either I. alopecuroides or I. myosuroides. Its distribution range includes the British Isles, western France and western Norway, with disjunct occurrences in Central Europe and Turkey. A molecular study was designed to clarify the taxonomic position of this taxon as well as to assess whether the disjunct populations in Germany are a result of recent migration or whether they are relicts of a wider distribution in more humid climatic periods. The analysis of nuclear ribosomal DNA sequences (ITS) revealed that Isothecium holtii is a good species, and that it is closer related to I. myosuroides than to I. alopecuroides. The disjunct populations in Germany are heterogenous. Two from the Harz Mts. cluster with different populations in Western Europe, indicating independent dispersal events, whereas another from the Eifel Mts. is genetically isolated, indicating a long separation and a relict. The populations in Brittany and the Massif Central in France are genetically related but rooted with the populations from Britain and Ireland and indicate that they are relicts of a former continuous range.<br /> The boreal moss Rhytidium rugosum, today widely but scattered spread over Europe, is considered to be a glacial relict of its wide but scattered holarctic range. Due to molecular data, it survived glaciation in southern European refugia, but also in some regions of central and western Europe. According to haplotypes distinguished in Europe, the species range is a result of migrations, range extension, colonization and spreading events. However, some relic haplotypes remain within some regions of Europe. The species extremely rarely produces spores and spreads mainly vegetatively. The geographical regions of higher genetic diversity among populations can be the regions where some relic haplotypes survived and afterwards were settled by some other haplotypes during migrations, as well. South-western and western Germany is determined as one of these region in Europe. According to molecular data sampled from selected European, American and Asian populations, a high genetic diversity of this species is present although it is mostly sterile. <br /> Dichelyma capillaceum is a rare and protected pleurocarpous moss from riparian habitats with scattered amphi-atlantic distribution. The European center of its distribution is concentrated within Scandinavia with 85 populations mostly in Sweden. Outside Scandinavia two further population are still present in Europe (in W. Germany and NW France). It is sterile although there are a few rare old records with sex organs or sporophyte from herbaria. The German population of D. capillaceum is genetically long time separated but originated from some ancestor from Scandinavia. According to the genetical data obtained it is rather result of relatively recent long distance dispersal event than of relict origin. Due to bio-geographical and molecular data, it can be assumed that the Scandinavian populations derived from North American. This can be proved by the fact that genetic variation among European populations studied is lower compared to all studied populations, which means a longer existence of American populations. It is furthermore is supported by the fact that atlantic North America is centre of species diversity of the genus Dichelyma. <br /> From the molecular data obtained, from the dispersal strategies of the species and from the geographical interpretations, the following conclusions can be drawn:<br /> 1. Both, long distance dispersal and relicts are responsible for the present distribution of the species studied. <br /> 2. The basal position of the southern and western European populations in species like Campylopus oerstedianus and Isothecium holtii supports the refugial hypothesis during the last Ice Age, from which the species established populations in Central Europe by long distance dispersal. The site of Dichelyma capillaceum in Germany has originated from the Scandinavian population by long distance dispersl, too. <br /> 3. In case of Hilpertia velenovskyi and Rhytidium rugosum, persistence during and since the last Ice Age in Central Europe can be postulated.<br /> 4. Long-distance dispersal is possible in the species studied, although they are sterile at present and lack specialized brood bodies. It can only be explained by the fact that fragments of plants can serve even for long distance dispersal.