Reidar Elven

Glacial survival or tabula rasa? The history of North Atlantic biota revisited

The possibility that northern refugia for arctic and boreal biota existed in geographic regions other than Beringia during the ice ages has stimulated continuous debates among botanists, zoologists, and geologists. A voluminous literature has accumulated presenting biogeographic and other evidence to propose numerous high-latitude refugia, such as nunataks protruding above the ice caps and exposed coastal shelves. Similar discussions have addressed possible “intraglacial” refugia in southern mountain regions, for example the European Alps (reviewed by Stehlik, 2002, 2003; Tribsch & Schönswetter, 2003). In this paper, we revisit the evidence proposed to support the hypothesis of “in situ glacial survival” (the “nunatak” hypothesis; originally formulated by Blytt, 1876, 1882; Warming, 1888; and Sernander, 1896) or the alternative “tabula rasa” hypothesis stating that postglacial immigration is responsible for the entire presentday biota in various North Atlantic regions. Up to the 1960s, there was virtually complete consensus among biogeographers that the occurrence of endemics and disjunct distributions in this area could not be explained without postulating in situ survival, at least during the last glaciation. In the concluding remarks for the Reykjavik Symposium on the North Atlantic Biota and their History, the Icelandic botanist Áskell Löve (1963: 391) stated that the theory of survival of plants within the glaciated areas replaces “the now merely historical tabula rasa idea”. In Scandinavia, many mountain plants were thought

Fifty thousand years of Arctic vegetation and megafaunal diet

Although it is generally agreed that the Arctic flora is among the youngest and least diverse on Earth, the processes that shaped it are poorly understood. Here we present 50 thousand years (kyr) of Arctic vegetation history, derived from the first large-scale ancient DNA metabarcoding study of circumpolar plant diversity. For this interval we also explore nematode diversity as a proxy for modelling vegetation cover and soil quality, and diets of herbivorous megafaunal mammals, many of which became extinct around 10 kyr bp (before present). For much of the period investigated, Arctic vegetation consisted of dry steppe-tundra dominated by forbs (non-graminoid herbaceous vascular plants). During the Last Glacial Maximum (25–15 kyr bp), diversity declined markedly, although forbs remained dominant. Much changed after 10 kyr bp, with the appearance of moist tundra dominated by woody plants and graminoids. Our analyses indicate that both graminoids and forbs would have featured in megafaunal diets. As such, our findings question the predominance of a Late Quaternary graminoid-dominated Arctic mammoth steppe.

Using next-generation sequencing for molecular reconstruction of past Arctic vegetation and climate

Palaeoenvironments and former climates are typically inferred from pollen and macrofossil records. This approach is time‐consuming and suffers from low taxonomic resolution and biased taxon sampling. Here, we test an alternative DNA‐based approach utilizing the P6 loop in the chloroplast trnL (UAA) intron; a short (13–158 bp) and variable region with highly conserved flanking sequences. For taxonomic reference, a whole trnL intron sequence database was constructed from recently collected material of 842 species, representing all widespread and/or ecologically important taxa of the species‐poor arctic flora. The P6 loop alone allowed identification of all families, most genera (>75%) and one‐third of the species, thus providing much higher taxonomic resolution than pollen records. The suitability of the P6 loop for analysis of samples containing degraded ancient DNA from a mixture of species is demonstrated by high‐throughput parallel pyrosequencing of permafrost‐preserved DNA and reconstruction of two plant communities from the last glacial period. Our approach opens new possibilities for DNA‐based assessment of ancient as well as modern biodiversity of many groups of organisms using environmental samples.

Trans-Atlantic dispersal and large-scale lack of genetic structure in the circumpolar, arctic-alpine sedge Carex bigelowii s. l. (Cyperaceae).

Paradoxically, several of the ecologically most important plant groups in the Arctic are little understood in terms of taxonomy and biogeographic history. The circumpolar Carex bigelowii s. l. (Cyperaceae) is abundant in the Arctic and is one of the most complicated arctic plant groups. While its ecology and population genetics have been extensively studied, its taxonomy is largely unexplored. We analyzed the large-scale geographical structuring of amplified fragment length polymorphisms (AFLPs) covering most of the distribution range. We detected high levels of genetic variation, most (66%) within populations, and a fairly weak genetic structure. Only the Central Asian populations, referred to as C. orbicularis, were strongly divergent. For the remaining populations, Bayesian clustering separated three distinct clusters (one European, one amphi-Atlantic, and one broadly amphi-Beringian), probably reflecting different major glacial refugia and recent transoceanic dispersal. The isolated central European populations were most closely related to those from a larger distribution area in northern Europe. Differences in genetic diversity suggest that the Alpine and Tatra populations have experienced strong bottlenecks, whereas the Krkonoše population may have been part of a continuous distribution area during the cold stages of the Pleistocene. Finally, we discuss the relevance of our results for a uniform, range-wide taxonomic concept.

Northern hemisphere biogeography of Cerastium (Caryophyllaceae): insights from phylogenetic analysis of noncoding plastidnucleotide sequences

Phylogenetic relationships and biogeography of the genus Cerastium were studied using sequences of three noncoding plastid DNA regions (trnL intron, trnL-trnF spacer, and psbA-trnH spacer). A total of 57 Cerastium taxa was analyzed using two species of the putative sister genus Stellaria as outgroups. Maximum parsimony analyses identified four clades that largely corresponded to previously recognized infrageneric groups. The results suggest an Old World origin and at least two migration events into North America from the Old World. The first event possibly took place across the Bering land bridge during the Miocene. Subsequent colonization of South America occurred after the North and South American continents joined during the Pliocene. A more recent migration event into North America probably across the northern Atlantic took place during the Quaternary, resulting in the current circumpolar distribution of the Arctic species. Molecular clock dating of major biogeographic events was internally consistent on the phylogenetic trees. The arctic high-polyploid species form a polytomy together with some boreal and temperate species of the C. tomentosum group and the C. arvense group. Lack of genetic variation among the arctic species probably indicates a recent origin. The annual life form is shown to be of polyphyletic origin.

Biogeography and Phylogeny of Cardamine (Brassicaceae)1

Abstract The biogeography and phylogeny of Cardamine L. were inferred based on sequences of the nuclear ribosomal ITS regions and the plastid trnL intron and trnL-F spacer regions. This genus is one of the largest and polyploid-rich genera of the Brassicaceae and has its center of diversity in Eurasia. Species were included from all populated continents, representing all sections except two monotypic ones. The results support a hypothesis of recent and rapid speciation in the genus. The traditional sectional classification was not supported. We found evidence for several extremely long-distance dispersal events. Colonization of the Southern Hemisphere and the Arctic has occurred repeatedly; we identified at least three phylogenetically distinct Arctic lineages, two distinct Oceanian lineages, and four distinct South American lineages. Polyploidization has occurred independently many times during the evolution of Cardamine. Recent divergence combined with widespread polyploidization offer an explanation for the complex taxonomy of the genus.

Taxonomy and Evolutionary Relationships in the Saxifraga rivularis Complex

Abstract In many arctic-alpine plant groups, reticulate evolutionary histories have resulted in problems with species delimitation and phylogenetic reconstruction. In the Saxifraga rivularis complex (2n  =  26, 52), the number of species accepted ranges from a single polymorphic one (S. rivularis s.l.) to several (the circumpolar S. hyperborea, the amphi-Atlantic S. rivularis, the three amphi-Pacific species S. bracteata, S. flexuosa, and S. arctolitoralis, and S. debilis in the Rocky Mountains). A combination of molecular (AFLPs), flow cytometrical, and morphological data from samples covering most of the distribution range was used to delimit taxonomic species and to unravel their evolutionary relationships. Four lineages with distinct morphological differences were recognized, representing four species: the diploids S. bracteata, S. hyperborea (including S. flexuosa), and S. debilis, and the tetraploid S. rivularis (including S. arctolitoralis). Based on a synthesis of the available data we provide a taxonomic revision of the complex and propose one rank change (S. rivularis subsp. arctolitoralis comb. et stat. nov.). Genome sizes as well as the intermediate position of the S. rivularis lineage in the molecular and morphological analyses suggest a single allopolyploid origin from the S. bracteata and the S. hyperborea lineages, most likely in Beringia.

Responses of alpine snowbed vegetation to long-term experimental warming

Abstract: In order to assess the influence of experimental warming on individual species response, species composition and richness, and the abundance of ramets in a wet late-melting snowbed, we established 20 open-top chambers (OTCs) permanently for 5 y (six growing seasons) at Finse, southwest Norway. Salix herbacea, Saxifraga stellaris, Omalotheca supina, Cerastium cerastoides, and Epilobium anagallidifolium increased in the experimentally warmed plots, while there was no significant response in Carex lachenalii, Deschampsia alpina, Poa alpina, Juncus biglumis, Saxifraga rivularis, or Veronica alpina. Species composition changed significantly with time both in the OTCs and in the control plots. Although invasion rates slightly increased in the OTCs compared to the controls, differences in overall species composition or richness were not significant between the OTCs and the control plots during the 5-y study. Our results suggest that vegetation change is going on naturally and that the effect of this change overrides the effect of the temperature treatment. We conclude that increased plant growth will result in denser vegetation in a warmer future. Whether the higher net invasion will result in more diverse vegetation is yet unclear, as the processes take more time than allowed for in this study.

Molecules and morphology in concert. II. The Festuca brachyphylla complex (Poaceae) in Svalbard

We used a combined molecular and morphological approach to unravel variation in the autogamous Festuca brachyphylla polyploid complex in the arctic archipelago of Svalbard. Forty populations were analyzed for random amplified polymorphic DNAs (RAPDs) and 46 morphological characters. Eighteen RAPD multilocus phenotypes were observed in the 86 plants analyzed, based on 30 polymorphic markers. Multivariate analyses of the RAPD data revealed four distinct groups of multilocus phenotypes; in contrast, the variation was more or less continuous in multivariate analyses of the morphological data. However, we identified several individual morphological characters that unambiguously discriminated among the four groups of RAPD multilocus phenotypes. Analysis of type material suggests that the four groups in Svalbard can be referred to Festuca baffinensis, F. brachyphylla, F. hyperborea, and F. edlundiae. This study shows that concerted analysis of molecules and morphology is a powerful tool in low-level taxonomy.

Long-distance plant dispersal to North Atlantic islands:colonization routes and founder effect

Our study provides new knowledge of two processes that are important for plant adaptation in a changing environment: 1) long-distance dispersal patterns, and 2) genetic founder effect on islands. Although the theoretical framework for the genetic founder effect on islands was proposed in 1973, we are the first to quantify it in relation to island size, dispersal distance, and plant traits. In addition, our genetic results are mainly coherent with post-glacial colonisation rather than in situ glacial survival, and should therefore bring a final end to the 140-year-long glacial survival-tabula rasa debate among northern biologists.