Life history of Maurolicus muelleri in fjordic and oceanic environments

Life history parameters are compared for populations of Maurolicus muelleri from Norwegian fjords and the Norwegian Sea in 1995 and 1996. The mortality rate was higher in the oceanic population (2·55 for males, 2·00 for females) than in the fjords (1·15 for males, 0·97 for females). Fish from the Norwegian Sea population occupied a depth with higher light levels, which may have contributed to the higher mortality through increased visibility to predators. Differences in growth, condition and gonad weight indicated different resource levels caused by different population densities. Recruitment was weak in many fjords in 1994, but not in the Norwegian Sea. It is suggested that wind-generated advection may affect recruitment in fjords on the western coast of Norway.     

Late-glacial vegetational ecotones and climatic patterns in Western Norway

The mapping of Weichselian late-glacial interstadial (13-11 ka B.P.) and Younger Dryas stadial (11-10 ka B.P.) pollen percentages for selected taxa demonstrates vegetational and hence climatic differentiation in Western Norway during these times. In the south, early interstadial Salix dominance was replaced by Betula woodland development. During Younger Dryas time, Betula pollen declined to values consistent with a modern vegetational analogue of the vegetation at the upper forest limit. In the inner fjord areas north of Stavanger, the interstadial vegetation contained scattered birch trees, the density depending on local topography and soils. During the Younger Dryas, vegetation resembling the modern mid- and low-alpine vegetation developed. On the outer coast, the interstadial vegetation was probably treeless, and dominated by Salix spp., including S. herbacea, and herbs. The vegetation became even more open during the Younger Dryas, resembling that of the modern mid- and high-alpine zones. The spatial ecotones delimiting the three areas of different vegetation development during both the interstadial and the Younger Dryas can be placed north of Stavanger, separating the southern region, and between the outer coast and inner fjord areas to the north. The Younger Dryas drop in temperature in all areas was up to about 5°C, enough to pass ecotonal thresholds in time in all areas.     

Genetic response to human‐induced habitat changes in the marine environment: A century of evolution of European sprat in Landvikvannet,Norway

Habitat changes represent one of the five most pervasive threats to biodiversity. However, anthropogenic activities also have the capacity to create novel niche spaces to which species respond differently. In 1880, one such habitat alterations occurred in Landvikvannet, a freshwater lake on the Norwegian coast of Skagerrak, which became brackish after being artificially connected to the sea. This lake is now home to the European sprat, a pelagic marine fish that managed to develop a self‐recruiting population in barely few decades. Landvikvannet sprat proved to be genetically isolated from the three main populations described for this species; that is, Norwegian fjords, Baltic Sea, and the combination of North Sea, Kattegat, and Skagerrak. This distinctness was depicted by an accuracy self‐assignment of 89% and a highly significant F _ST between the lake sprat and each of the remaining samples (average of ≈0.105). The correlation between genetic and environmental variation indicated that salinity could be an important environmental driver of selection (3.3% of the 91 SNPs showed strong associations). Likewise, Isolation by Environment was detected for salinity, although not for temperature, in samples not adhering to an Isolation by Distance pattern. Neighbor‐joining tree analysis suggested that the source of the lake sprat is in the Norwegian fjords, rather than in the Baltic Sea despite a similar salinity profile. Strongly drifted allele frequencies and lower genetic diversity in Landvikvannet compared with the Norwegian fjords concur with a founder effect potentially associated with local adaptation to low salinity. Genetic differentiation (F _ST) between marine and brackish sprat is larger in the comparison Norway‐Landvikvannet than in Norway‐Baltic, which suggests that the observed divergence was achieved in Landvikvannet in some 65 generations, that is, 132 years, rather than gradually over thousands of years (the age of the Baltic Sea), thus highlighting the pace at which human‐driven evolution can happen.     

Genetic differentiation between Arctic and Antarctic monothalamous foraminiferans

Monothalamous (single-chambered) foraminifers are a major component of the benthic meiofauna in high latitude regions. Several morphologically similar species are common in the Arctic and Antarctic. However, it is uncertain whether these morphospecies are genetically identical, or whether their accurate identification is compromised by a lack of distinctive morphological features. To determine the relationship between Arctic and Antarctic species, we have compared SSU rDNA sequences of specimens belonging to four morphotaxa: Micrometula, Psammophaga, Gloiogullmia, and one morphospecies Hippocrepinella hirudinea from western Svalbard (Arctic) and McMurdo Sound (Antarctic). Wherever possible, we include in our analyses representatives of these taxa from the deep Arctic and Southern Oceans, as well as from Northern European fjords. We found that in all cases, the bipolar populations were clearly distinct genetically. As expected, Arctic specimens were usually more closely related to those from Northern Europe than to their Antarctic representatives. The deep-sea specimens from Weddell Sea branched as a sister to the McMurdo Sound population, while those from the Arctic Ocean clustered with ones from Norwegian fjords. Our study has revealed a high number of cryptic species within each of the examined genera, and demonstrates the unexplored potential of monothalamous foraminifers for use as a tool to evaluate the origin and biogeography of polar meiofauna.     

Habitats and Distribution Patterns of Marine Luminous Bacteria in the Western Baltic Sea

Numbers of luminous bacteria were counted at three stations of the brackish water ecosystem of the western Baltic Sea from July 1985 to July 1986. Additional samples were taken during three cruises from stations at the North Atlantic Ocean, the Norwegian Sea and adjacent marine areas. — In Kiel Bight (western Baltic) values varied between 0 and 68,000 luminous cfu 1⁻¹. With exception of the coastal station a distinct seasonal distribution pattern was shown in a water depth of 20 m: high numbers found in summer were opposed to low numbers in winter, the peaks being rather high in comparison to those of other areas. Statistical analysis showed that the results of 20 m were significantly different from those of 0 and 10 m depth; however, there was no correlation with temperature and salinity. Taxonomic studies revealed that the population consisted primarily of the genus Photobacterium. — The optimum of salinity was not a brackish but a marine one and was about 30% for the majority of the strains tested. A smaller number of strains grew best at a salinity between 10 and 15%. Optima of temperature ranged from 15 to 20 °C for most of the test strains. — Taxonomic analysis was also performed with luminous strains from marine areas adjacent to the western Baltic Sea, Photobacterium being the dominant genus here, too. Luminous bacteria were also enriched from the external surface and the gut contents of whitings (Merlangius merlangus) and cods (Gadus morhua). A model is proposed which explains the distribution pattern found. According to this, the gut-dwelling luminous bacteria are transported by their hosts from the North Sea into the western Baltic Sea. Here they are released into the environment, thus inhabiting another niche.     

Paleoceanographic history around the Tsugaru Strait between the Japan Sea and the Northwest Pacific Ocean since 30 cal kyr BP

The paleoceanographic history around the Tsugaru Strait since 30.0 cal kyr BP was reconstructed using ecological and biogeographical habitats of diatom species and Q-mode factor analysis of diatom flora in six piston cores. At 30.0-17.5 cal kyr BP, a fall in sea level and the intensification of the Oyashio Current caused erosion of submarine sediments near the shore in the eastern area of the Strait and led to deposition of the third and second sequences of thinly laminated layers (TL3 and TL2) in the Japan Sea. At 17.5-11.5 cal kyr BP, cooling intensified around the Strait, producing an inflow of Oyashio water into the Japan Sea through the Strait. At 15.5-14.5 cal kyr BP, a cold-water mass around the Strait developed from subarctic sea-ice to arctic waters. At 13.0-11.2 cal kyr BP, the Younger Dryas cooling was clearly recorded by the increasing of oceanic cold-water diatom species in the eastern area of the Tsugaru Strait but not in the Japan Sea. At 15.5-13.0 cal kyr BP and 11.25-10.25 cal kyr BP, the warming around the Younger Dryas resulted in the deposition of thinly laminated layers off Shimokita in the eastern area of the Strait. At 9.5 cal kyr BP, the Oyashio Current water intruded into deep depths in the mixed water region off Sanriku. At 9.5-7.0 cal kyr BP, the fluctuation of 1.5-kyr intervals in the strength of the Tsushima Warm Current system in the Japan Sea was initiated.     

Depth-related radiolarian assemblage in the water-column and surface sediments of the Japan Sea

Plankton tows and surface sediments from the Japan Sea, a marginal sea of the northwestern Pacific, were examined to study the depth distribution of modern radiolarians. The depth distribution patterns between the living assemblage in the water-column and the thanatocoenose in surface sediments are similar to each other, indicating that the depth-related assemblage in sediments is closely related to the living depths of major species. Four clear restrictions of many species to discrete depth zones are recognized in the water-column, from the surface down to 2000 m: (1) upper subsurface-water species, which are abundant from 40 to 120 m (Larcopyle butschlii juvenile form, Spirocyrtis subscalaris, Spongodiscus resurgens and Lipmanella virchowii); (2) lower subsurface-water species, which are abundant from 40 to 300 m (Larcopyle butschlii adult form, Ceratocyrtis histricosa and Spongotrochus glacialis); (3) intermediate-water species, which have population maxima from 160 to 300 m (Ceratospyris borealis); and (4) deep-water species, which have maxima between 1000 and 2000 m (Cycladophora davisiana and Actinomma boreale). Only a few specimens of A. boreale were found in the water-column ranging from 1000 to 2000 m depth, although this is a dominant species in surface sediments from depths below 2000 m of which the dominance increases with water depth. A. boreale may live mainly in the bottom water. Cycladophora davisiana and A. boreale, which characterize the Japan Sea deep assemblage, are naturally shallow or intermediate dwellers in other oceans. On the other hand, the typical deep-dwellers (e.g. Cornutella profunda, Cyrtopera languncula and Peripyramis circumtexta) of other oceans have not been found in the Japan Sea. Such a peculiar deep assemblage is a result of the deep circulation system in the Japan Sea and the shallow depths of the sills around it.     

Structure and specific features of formation of aggregations of deepwater redfish <Emphasis Type="Italic">Sebastes mentella</Emphasis> (Scorpaenidae) in the Norwegian Sea pelagial

Results of studies of the structure and specific features of formation of aggregations of deepwater redfish Sebastes mentella in the Norwegian Sea pelagial are provided. Data on the biological characteristics of S. mentella from different regions of the Norwegian Sea pelagial do not allow us to consider its aggregations as separate populations. On the basis of comparative analysis of the structure of aggregations in the Norwegian Sea and of population parameters and specific features of the life cycle of S. mentella in different parts of the Atlantic Ocean, its complex intraspecies organization at sites of overlapping of two largest populations—North Atlantic and Norwegian-Barents Sea-was established. The formation of pelagic aggregations in the water area of the Norwegian Sea occurs due to migration of maturing and mature individuals from the adjoining water areas. In the southern areas of the Norwegian Sea, dominant recruitment comes from the pelagial of the northeastern part of the Irminger Sea, which is promoted by the direction of streams of the North-Atlantic Current; it is not excluded either that fish can migrate to the southern part of the sea from the slopes of the Faeroes, Faeroes-Icelandic threshold, and the western coast of Norway. Migration to the northern areas of the sea is mainly performed by rapidly maturing fish from the rearing region from the western slopes of the Barents Sea and Spitsbergen Archipelago. The presence of seasonal migrations hinders the formation in the pelagial of perch isolated groups and promotes their migration.     

Reconstruction of Late Pleistocene-Holocene palaeobathymetries from Ostracoda on the Tyrrhenian continental shelf

Quantitative analyses of ostracod assemblages from three cores recovered on the Tyrrhenian shelf (Gaeta and Salerno Gulfs) have been applied to construct palaeobathymetric curves. Palaeoclimatic curves obtained from planktonic foraminifera, calcareous nanoplankton, pteropods and pollen are available for the same cores, in addition to sedimentological, mineralogical, geochemical (δ¹⁸O, ¹⁴C, C/N, CaCO₃) and volcanological data with regard to the two cores from the Salerno Gulf. The palaeobathymetric curves reflect the climatic events through the Late Pleistocene-Holocene interval. The climatic events of the Last Glacial (and within it, the Last Glacial Maximum), the Late Glacial (with Oldest Dryas, Bølling-Allerød, Younger Dryas events) and Postglacial have been recognised. The palaeobathymetric curves are also in agreement with palaeoclimatic curves of planktonic assemblages and pollen.     

Late Pleistocene-Holocene radiolarian paleotemperatures in the Norwegian Sea based on artificial neural networks

Artificial Neural Networks (ANN) were trained by using an extensive radiolarian census dataset from the Nordic (Greenland, Norwegian, and Iceland) Seas. The regressions between observed and predicted Summer Sea Temperature (SST) indicate that lower error margins and better correlation coefficients are obtained for 100 m (SST₁₀₀) compared to 10 m (SST₁₀) water depth, and by using a subset of species instead of all species. The trained ANNs were subsequently applied to radiolarian data from two Norwegian Sea cores, HM 79-4 and MD95-2011, for reconstructions of SSTs through the last 15,000 years. The reconstructed SST is quite high during the Bølling-Allerød, when it reaches values only found later during the warmest phase of the Holocene. The climatic transitions in and out of the Younger Dryas are very rapid and involve a change in SST₁₀₀ of 6.2 and 6.8 °C, taking place over 440 and 140 years, respectively. SST₁₀₀ remains at a maximum during the early Holocene, and this Radiolarian Holocene Optimum Temperature Interval (RHOTI) predates the commonly recognized middle Holocene Climatic Optimum (HCO). During the 8.2 ka event, SST₁₀₀ decreases by ca. 3 °C, and this episode marks the establishment of a cooling trend, roughly spanning the middle Holocene (until ca. 4.2 ka). Successively, since then and through the late Holocene, SST₁₀₀ follows instead a statistically significant warming trend. The general patterns of the reconstructed SSTs agree quite well with previously obtained results based on application of Imbrie and Kipp Transfer Functions (IKTF) to the same two cores for SST₀. A statistically significant cyclic component of our SST record (period of 278 years) has been recognized. This is close to the de Vries or Suess cycle, linked to solar variability, and documented in a variety of other high-resolution Holocene records.     

The contribution of single and colonial cells of Phaeocystis pouchetii to spring and summer blooms in the north-eastern North Atlantic

Studies of the phytoplankton ecology in different localities in north-Norwegian fjords, the White Sea and the Barents Sea were carried out in spring and early summer to investigate the contribution of single and colonial stages of Phaeocystis pouchetii to phytoplankton abundance. Three different types of flagellated and four colonial cells were observed in all localities. P. pouchetii was rare under the ice of the Barents and White Seas, but their abundance increased rapidly during ice retreat. Single cell C dominated over colonial cell C, often by 50 times or more. The highest share of colonial cells was encountered in April in northern Norwegian fjords, in May in the Barents Sea and in May–June in the White Sea. At times the single cell dominated the total P. pouchetii biomass in Balsfjord (April 1999, 2001) with hardly any colonies present. In the White Sea colonies of P. pouchetii were less abundant than in the other regions. Cell carbon of P. pouchetii colonies appears never to be as dominating in the north-eastern North Atlantic as P. globosa blooms in coastal regions such as the southern North Sea. However, the lobal matrix of P. pouchetii colonies appears to be less solid than that of P. globosa and partly dissolution of the colony matrix during handling and storage of fixes samples induces uncertainty about the absolute numbers of P. pouchetii colonial cell counts. Despite of that, single cells of P. pouchetii seem to dominate significantly over colonial cell biomass at most sites and during some years and in some regions colonial cells seem rare. We speculate that top-down regulation of Phaeocystis spp. blooms possibly determines the ratio between single and colonial cells.     

Causes for mass occurrences of the jellyfish Periphylla periphylla: a hypothesis that involves optically conditioned retention

The mesopelagic coronate medusa Periphylla periphylla has beenvery abundant (20–320 individuals m^–2), with asmany as 2.5 individuals m^–3, for more than a decade incertain Norwegian fjords. These abundances are two to threeorders of magnitude higher than reported from open ocean environments.Comparisons of the size, density and behavior of this jellyfishin three fjords (Lurefjorden, Sognefjorden and Halsafjorden)support the hypothesis that retention of P. periphylla is relatedto basin topography, light attenuation and photosensitivity.Furthermore, we hypothesize that the abundances of P. periphyllain Lurefjorden and Halsafjorden, but not in Sognefjorden, havebeen stimulated by increased light absorbance of water massesformed in the North Sea.     

The distribution, natural habitats and availability of wild cereals in relation to their domestication in the Near East: multiple events, multiple centres

In this article we examine the natural habitats and distribution of the six wild cereals: Triticum urartu (wild urartu wheat), T. boeoticum aegilopoides (single-grained wild einkorn), T. boeoticum thaoudar (two-grained wild einkorn), T. dicoccoides (wild emmer wheat), Secale spp. (wild ryes) and Hordeum spontaneum (wild barley). A comparison of late Pleistocene/early Holocene archaeobotanical assemblages in the Near East with present-day distributions of wild cereals shows a good correlation. The regional variation in the archaeobotanical cereal assemblages and the ensuing domestication provide evidence that different cereal species were domesticated independently in different areas. Some sites were not situated near wild cereal habitats and a few were located outside the limits of distribution, even accounting for moister climatic conditions. I argue here that current models which try to explain the shift to farming have tended to over-emphasize the effect of the Younger Dryas climatic change. First, it would have had only a minor effect on cereal availability. Secondly, agriculture appears to have been established after the Younger Dryas. Thirdly, there is no evidence for a single centre of origin; agriculture arose in widely separated geographic and climatic regions. And fourthly, agriculture depends on stable climatic conditions which were not established until after the Younger Dryas.     

Evidence for Two Highly Differentiated Herring Groups at Goose Bank in the Barents Sea and the Genetic Relationship to Pacific Herring, Clupea pallasi

Genetic studies on Atlantic herring, Clupea harengus, have generally revealed a low level of genetic variation over large geographic areas. Genetically distinct herring populations in some of the Norwegian fjords are exceptions, and juvenile herring from the large oceanic herring, Norwegian Spring Spawners (NSS), are often found in mixture with local fjord populations as well as widely distributed in the Barents Sea. Research surveys in the eastern Barents Sea (Goose Bank) in 1993, 1994 and 2001 included collection of herring samples for allozyme analyses. As expected the results identified juveniles from NSS stock, but an additional unique group of herring (low vertebrae number), being almost fixed for alternative alleles at several allozyme loci, was detected. In some cases, the two groups of herring were taken in the same trawl catches as documented by highly significant departure from Hardy—Weinberg expectation with large excess of homozygotes providing evidence for population mixing. Large genetic differences (Nei's genetic distance = 1.53; F_ST = 0.754) were detected in pairwise comparisons based on five allozyme loci. The two herring groups were also compared with reference samples of Pacific herring, Clupea pallasi, including one sample from Japan Sea and three Alaskan samples. UPGMA dendrogram based on five allozyme loci revealed a close genetic relationship between the low vertebrae herring in the Barents Sea and the group of samples of Pacific herring. Although significant different in allele frequencies, one of the herring samples clustered together with the reference sample from Bering Sea with genetic distance of 0.008 and F_ST value of 0.032. The close genetic relationship found in this paper, suggest a re-evaluation of the taxonomic status of the Barents Sea herring populations investigated.     

Late Weichselian and Holocene sedimentary environments and ice rafting in Isfjorden, Spitsbergen

Multi-proxy analyses of two sediment cores from central Isfjorden were used to reconstruct the glacial history in central Spitsbergen during the Late Weichselian and the Holocene, and to relate iceberg rafting and sea-ice rafting to climatic and oceanographic changes in the north Atlantic region. A basal till was deposited beneath an ice stream prior to 12,700 cal. years BP (calendar years before the present). Several tidewater glaciers influenced the sedimentary environment during the Younger Dryas and probably already during the Allerød. The Younger Dryas cooling might be reflected by enhanced sea-ice formation and suspension settling, as well as reduced iceberg rafting. The final deglaciation was dominated by intense iceberg rafting. It terminated around 11,200 cal. years BP. Optimum Holocene climatic and oceanographic conditions with significantly reduced ice rafting occurred between c. 11,200 and 9000 cal. years BP. Ice rafting occurred almost exclusively from icebergs after 10,200 cal. years BP. The icebergs most probably originated from tidewater glaciers on east Spitsbergen, indicating the presence of a strong east–west temperature gradient at this time. An increase of iceberg rafting around 9000 cal. years BP, followed by enhanced sea-ice rafting, reflects the onset of a general cooling in the western Barents Sea–Svalbard region. Comparatively intense rafting from icebergs and sea ice between 9000 and 4000 cal. years BP is related to this cooling. A general reduction in ice rafting after 4000 cal. years BP is most probably the result of the enhanced formation of shore-fast and/or more permanent sea-ice cover, reducing the drift of icebergs and sea ice in the fjord. The results indicate that the palaeoenvironmental conditions on central Spitsbergen to a large degree depended on the oceanographic conditions in the western Barents Sea and west off Spitsbergen. However, climatic trends affecting Greenland and the entire north Atlantic region can also be identified.     

Glacial Holocene environment of the southeastern Okhotsk Sea: evidence from geochemical and palaeontological data

Environmental conditions and productivity changes in the southeastern Okhotsk Sea have been reconstructed for the last 20 ka using planktonic and benthic foraminiferal oxygen isotope records and calcium carbonate, organic carbon and opal content data from two sediment cores. Species variability in benthic foraminiferal and diatom assemblages provides additional palaeoceanographic evidence. AMS radiocarbon dating of the sediments and oxygen isotope stratigraphy serve as the basis for the age models of the cores for the last 20 ¹⁴C kyr and for correlation between environmental variations in the Okhotsk Sea, and regional and global climate changes. Benthic foraminiferal assemblages in the two cores (depth 1590 and 1175 m) varied with time, so that we could recognise seven zones with different species composition. Changes in the benthic foraminiferal assemblages parallel major environmental and productivity variations. During the last glaciation, fluxes of organic matter to the sea floor showed strong seasonal variations, indicated by the presence of abundant A. weddellensis and infaunal Uvigerina spp. Benthic foraminiferal assemblages changed with warming at 12.5–11 and 10–8 ¹⁴C kyr BP, when productivity blooms and high organic fluxes were coeval with global meltwater pulses 1A and 1B. Younger Dryas cooling caused a decline in productivity (11–10 kyr BP) affecting the benthic faunal community. Subsequent warming triggered intensive diatom production, opal accumulation and a strong oxygen deficiency, causing significant changes in benthic fauna assemblages from 5.26–4.4 kyr BP to present time.     

Evidence of Large Change in Unionid Mussel Abundance from Selective Muskrat Predation,as Inferred by Shell Remains Left on Shore

Three species of unionid mussels (Pyganodon grandis, Lampsilis siliquoidea, and Toxolasma parvus) were preyed on by muskrats (Ondatra zibethicus) that left shell remains at feeding sites (middens) along the shore of Lake LaSalle (West) in western New York State, USA. Mussels became established within five years of the construction of this small artificial lake, and individuals of all three species have grown rapidly to large size. The abundance of prey in middens in 1988–1990 and a marked decline in subsequently deposited shells indicate how dramatically muskrats had exploited this food source. They consumed > 2700 individuals of P. grandis (by far the most common prey item) through 1990, yet only 20 newly deposited shells were found in 1993. At a midden where prey depletion was directly catalogued during 1988, larger specimens of P. grandis were consumed first, suggesting size selection. L. siliquoidea has been least affected by predation, and was the mussel most often found alive in the littoral zone. No live T. parvus were ever collected, and this species is known only from middens. Complete collections of shell remains from the shoreline through 1999 suggest that the mussel population may be recovering slowly. Muskrat predation may be more important in influencing mussel population structure than previously realized, and the effects can be dramatic spatially and temporally.     

<Emphasis Type="Italic">Actinostola callosa</Emphasis> (Verrill, 1882) (Actinostolidae,Anthozoa), a medusivorous sea anemone and its mass occurrence in the Lurefjord,Norway

The seafloor of two Norwegian fjords (Lurefjord and Sognefjord) was studied using a remotely operated vehicle (ROV). Two large sea anemone species, Actinostola callosa and Bolocera tuediae, are part of the benthic fauna of these fjords. The first species is the most abundant in the Lurefjord north of Bergen. A special linear model to calculate the distances between specimens was constructed using the Geographic Information System data from the ROV. A. callosa was found to be medusivorous. Its biomass and high abundance seem to be correlated with a mass occurrence of its important local prey, the coronate medusa Periphylla periphylla.Communicated by H.-D. Franke     

Late Quaternary history of Hippophaë rhamnoides L. (Elaeagnaceae) inferred from chalcone synthase intron (Chsi) sequences and chloroplast DNA variation

Fossil pollen records indicate that Hippophaë rhamnoides (Sea Buckthorn) was widespread on late‐ and early postglacial raw soils throughout much of central and northern Europe, but that Early Holocene reforestation restricted populations to northern coastal habitats, or along mountain streams in the Alps, Pyrenees, and Carpathians. We used sequence variation at the nuclear chalcone synthase intron (Chsi), in conjunction with chloroplast DNA–restriction fragment length polymorphism data, to investigate the intraspecific phylogeny, phylogeographic structure, and expansion demographic history of this dioecious and wind‐pollinated shrub at its range‐wide scale in Europe and Asia Minor. Four major Chsi phylogroups of unresolved relationships were identified with estimated divergences ～172 000 years ago. Large‐scale phylogeographic structures of nuclear and cytoplasmic markers were congruent in identifying (i) southeastern Europe as the most likely source of colonization into central Europe and Scandinavia, and (ii) the area just north of the Alps as a contact zone between populations from the Alps and the east/central European‐Scandinavian lineage. Coalescence‐based analyses (i.e. nested clade analysis and mismatch distributions) of Chsi variation were able to detect at least four major episodes of population growth, all within about the last 40 000 years. In particular, these analyses identified a nearly synchronized timing of population expansions in various parts of the species’ range in central‐eastern Europe/Asia Minor, most likely correlating with the Younger Dryas Stadial (～13 000–11 600 years ago). It remains to be established whether the phylogeographic history of H. rhamnoides, and particularly its rapid response to the rapid environmental changes of the Younger Dryas cold snap, is unique to the species, or whether it is shared with other cold‐tolerant shrub (or grassland) species known from late‐glacial raw soils in Europe.     

How long was the Younger Dryas? Preliminary evidence from annually laminated sediments of Soppensee (Switzerland)

Despite extensive AMS-¹⁴C dating series on Late-glacial terrestrial plant remains, a precise estimate of the duration of the Younger Dryas biozone (sensu Ammann & Lotter, 1989) is hampered by the occurrence of a period of constant ¹⁴C-age at 10 000 yr B.P. However, varve counts at Soppensee suggest that the Younger Dryas biozone comprises approx. 680–720 varves, and that the phase of constant radiocarbon age includes between 270–310 varves.