Microrefugia

The concept of microrefugia is widely accepted to explain the post-glacial colonization of continents, which led to the present-day biotic configuration of the Earth. However, so far, microrefugia are no more than a 'theoretical necessity' without an appropriate biogeographical and ecological characterization. Here, a tentative definition and a classification of microrefugia, based on the existing literature, are proposed for discussion. A deeper biogeographical analysis of the concept is suggested using novel ecological models and methods, in order to develop new hypotheses to be tested with palaeoecological and molecular phylogenetic tools.     

Plant remains from the Kreftenheye Formation (Eemian) at Raalte,The Netherlands

The Kreftenheye Formation is a fluviatile deposit occurring in the central part of the Netherlands. The present study deals with the plant remains found in suction-dredged bulk samples from its largely Eemian Zutphen Member, a clayey sediment formerly known as the clay–peat bed or the Salvinia bed. It reports the discovery of a large number of galls induced by the asexual generation of the currently southeast European oak gall wasp Andricus hungaricus. The associated plant remains include seeds, fruits, conifer cones, wood, spines, leaf fragments, buds, bud scales, stem fragments, bryophytes, sporangia, oospores, palynomorphs, galls, jet and amber. The palynomorph samples indicate the Late Eemian pollen zone E5b of the Carpinus phase as the origin of the galls, but the other macrofossils may have a wider stratigraphic range, including possibly also material from (a part) of the zones E3–E5a. Several elements, such as Celtis, Chamaecyparis, Juglans, Magnolia and Pterocarya, date almost certainly from earlier interglacials. The list of plant remains is dominated by fresh water plants, riparian elements and ancient woodland taxa, which reflects the ecological range of the IJssel valley and adjacent ice-pushed ridges very well. Thermophilous elements include Brasenia schreberi, Buxus sempervirens, Cornus mas, Najas minor, Salvinia natans, Trapa natans and possibly also Andricus hungaricus. Quercus cerris, the probable host of the sexual generation of A. hungaricus was not found.     

Refugial origins of reindeer (Rangifer tarandus L.) inferred from mitochondrial DNA sequences

The glacial-interglacial cycles of the upper Pleistocene have had a major impact on the recent evolutionary history of Arctic species. To assess the effects of these large-scale climatic fluctuations to a large, migratory Arctic mammal, we assessed the phylogeography of reindeer (Rangifer tarandus) as inferred from mitochondrial DNA (mtDNA) sequence variation in the control region. Phylogenetic relationships among haplotypes seem to reflect historical patterns of fragmentation and colonization rather than clear-cut relationships among extant populations and subspecies. Three major haplogroups were detected, presumably representing three separate populations during the last glacial. The most influential one has contributed to the gene pool of all extant subspecies and seems to represent a large and continuous glacial population extending from Beringia and far into Eurasia. A smaller, more localized refugium was most likely isolated in connection with ice expansion in western Eurasia. A third glacial refugium was presumably located south of the ice sheet in North America, possibly comprising several separate refugial populations. Significant demographic population expansion was detected for the two haplogroups representing the western Eurasian and Beringian glacial populations. The former apparently expanded when the ice cap retreated by the end of the last glacial. The large continuous one, in contrast, seems to have expanded by the end of the last interglacial, indicating that the warm interglacial climate accompanied by marine transgression and forest expansion significantly confined population size on the continental mainland. Our data demonstrate that the current subspecies designation does not reflect the mtDNA phylogeography of the species, which in turn may indicate that morphological differences among subspecies have evolved as adaptive responses to postglacial environmental change.     

The Pleistocene easternmost distribution in Eurasia of the species associated with the Eemian Palaeoloxodon antiquus assemblage

• 1 The Palaeoloxodon antiquus large‐mammal assemblage was typical of the late middle and late Pleistocene interglacials in Europe. This review examines the assemblage's origins, dispersal and cohesiveness in Eurasia.
• 2 During the more climatically equable middle‐Pleistocene periods, the Palaeoloxodon assemblage (or closely related) species occurred across central Eurasia almost simultaneously. In Central and Western Europe, these species responded to climatic changes together as an unvarying interglacial assemblage, whereas in Eastern Europe and Siberia, they occurred in diverging assemblages. The boundary of the Palaeoloxodon assemblage can be drawn roughly from Poland to Romania.
• 3 In Central and Western Europe this interglacial assemblage last occurred during the Eemian. During this period many of the Palaeoloxodon assemblage species may also have co‐occurred in south‐eastern Europe and, except for Bubalus murrensis and Hippopotamus amphibius, further eastwards. The extinct species of the Palaeoloxodon assemblage disappeared in Siberia and Central Asia prior to Europe and the Caucasus whereas the extant species were already present in their modern distribution areas.
• 4 A quantitative study of faunal associations across Eurasia, following much‐needed comprehensive systematic reviews, would further elucidate the patterns of faunal change associated with local and global climatic changes during the middle to late Pleistocene.

     

Global changes explain the long-term demographic trend of the Eurasian common lizard (Squamata: Lacertidae)

The demographic trend of a species depends on the dynamics of its local populations, which can be compromised by local or by global phenomena. However, the relevance of local and global phenomena has rarely been investigated simultaneously. Here, we tested whether local phenomena compromised a species’ demographic trend using the Eurasian common lizard Zootoca vivipara, the terrestrial reptile exhibiting the widest geographic distribution, as a model species. We analyzed the species’ ancient demographic trend using genetic data from its 6 allopatric genetic clades and tested whether its demographic trend mainly depended on single clades or on global phenomena. Zootoca vivipara’s effective population size increased since 2.3 million years ago and started to increase steeply and continuously from 0.531 million years ago. Population growth rate exhibited 2 maxima, both occurring during global climatic changes and important vegetation changes on the northern hemisphere. Effective population size and growth rate were negatively correlated with global surface temperatures, in line with global parameters driving long-term demographic trends. Zootoca vivipara’s ancient demography was neither driven by a single clade, nor by the 2 clades that colonized huge geographic areas after the last glaciation. The low importance of local phenomena, suggests that the experimentally demonstrated high sensitivity of this species to short-term ecological changes is a response in order to cope with short-term and local changes. This suggests that what affected its long-term demographic trend the most, were not these local changes/responses, but rather the important and prolonged global climatic changes and important vegetation changes on the northern hemisphere, including the opening up of the forest by humans.     

Evidence for a lacustrine faunal refuge in the Larsemann Hills, East Antarctica, during the Last Glacial Maximum

Aim  There is no previous direct evidence for the occurrence of lacustrine refuges for invertebrate fauna in Antarctica spanning the Last Glacial Maximum (LGM). In the absence of verified LGM lacustrine refuges many species are believed to result from Holocene dispersal from sub-Antarctic islands and continents further north. If freshwater lake environments were present throughout the LGM, extant freshwater species may have been associated with Antarctica prior to this glacial period. This study looked at faunal microfossils in a sediment core from an Antarctic freshwater lake. This lake is unusual in that, unlike most Antarctic lakes, the sediment record extends to c . 130,000 yr bp , i.e. prior to the LGM.
Location  Lake Reid, Larsemann Hills, East Antarctica (76°23' E; 69°23' S).
Methods  Palaeofaunal communities in Lake Reid were identified through examination of faunal microfossils in a sediment core that extended to c . 130,000 yr bp .
Results  Ephippia and mandibles from the cladoceran Daphniopsis studeri and loricae of the rotifer Notholca sp. were found at all depths in the sediment, indicating that these two species have been present in the lake for up to 130,000 years. Copepod mandibles were also present in the older section of the core, yet were absent from the most recent sediments, indicating extinction of this species from Lake Reid during the LGM.
Main conclusion  The presence of D. studeri and Notholca sp. microfossils throughout the entire Lake Reid core is the first direct evidence of a glacial lacustrine refugium for invertebrate animals in Antarctica, and indicates the presence of a relict fauna on the Antarctic continent.     

Taphonomy in the light of intrinsic shell properties and life habits: Marine bivalves from the Eemian of northern Russia

A taphonomic analysis of the bivalvesArctica islandica (Arcticidae),Astarte borealis (Astartidae),Mytilus edulis (Mytilidae), andSpisula elliptica (Mactridae) from shallow-marine last interglacial Sediments exposed along the Pyoza river, Arkhangelsk region, shows that they differ in preservation, probably because of differences in shell shape, shell structures, and life habits. The Shells indicate that the temporal sequence of taphonomic processes was as follows: (1) pre-mortem bioerosion and dissolution; (2) post-mortem bioerosion; (3) abrasion, disarticulation, and fragmentation; and (4) dissolution. A new graphic Illustration, the taphonomic constituent diagram (TCD), is proposed to illustrate the sequences of taphonomic processes. It is inspired by the ichnofabric constituent diagram used in ichnology and integrates the shell surface coverage of different taphonomic features by graphically plotting them against relative time. The taphonomic constituent diagram may display differences in the Chronologie order of paleoenvironmental processes. Also, the diagram enables a combination of both microscopic and macroscopic taphonomic features, and eases comparative studies of fossil assemblages.