The genus Stauroneis (Bacillariophyceae) in the Antarctic region

Aim To provide a detailed biogeography of the diatom genus Stauroneis in the Antarctic and sub‐Antarctic regions and to establish the biogeographical relationships between the different constituent locations to test the application of a precise and refined taxonomy in generating accurate polar biogeographies. Location The Antarctic and sub‐Antarctic region comprising the islands South Georgia, Crozet, Kerguelen, Marion, Heard and the Antarctic Peninsula. Methods Diatom samples from different habitats in a large part of the sub‐Antarctic and Antarctic region were investigated for their Stauroneis content. Presence/absence data were investigated using Sørensen's similarity index. An additional 500 samples from Arctic locations were used to provide a bipolar comparison. Using reliable literature data, gaps in the distribution of the Stauroneis taxa were filled. Results The Stauroneis flora of the Antarctic and sub‐Antarctic regions is quite distinct from its Arctic equivalent, with only five species (out of 60) common to both areas. Within the (sub‐)Antarctic group, the islands of the Indian Ocean have the most diverse Stauroneis composition, which is clearly separated from the rest of the region. The South Georgia Stauroneis composition has some affinities with the Antarctic Peninsula but the latter has far fewer species. These results are in clear contrast to older data showing no biogeographical difference between the Arctic and Antarctic regions. Main conclusions Using only a single genus, a clear biogeography of the (sub‐)Antarctic region can be produced that separates the Indian Ocean islands from other sampling locations. When based on a precise taxonomy, biogeographical relationships between locations in the region become much more reliable. Contrary to previous work, there is almost no similarity in the diatom floras of the Arctic and Antarctic regions.     

Diversity, ecology and biogeography of the freshwater diatom communities from Ulu Peninsula (James Ross Island, NE Antarctic Peninsula)

The diversity, ecology and biogeography of diatoms in lakes, seepage areas and streams on the Ulu Peninsula, a large ice-free area in the northern part of James Ross Island (Weddell Sea), were studied. A diverse diatom flora of 123 taxa was observed, dominated by several Nitzschia taxa, Psammothidium papilio, Eolimna jamesrossensis, Fragilaria capucina and Fistulifera saprophila. The results from the similarity and diversity analysis suggest James Ross Island to be biogeographically positioned within the Maritime Antarctic region, yet with some affinities with the flora of Continental Antarctica, as shown by the presence of Luticola gaussii and Achnanthes taylorensis. Based on our data, James Ross Island can thus be located close to the boundary of the two main Antarctic biogeographical regions. Diatom communities present in streams and seepage areas could be clearly distinguished from those in lakes, the latter being much more species rich. Based on the multivariate analysis, conductivity and nutrients were selected as the two main environmental factors determining the diatom composition in the Ulu Peninsula lakes. The revised taxonomy of the Antarctic diatom flora induced the construction of a transfer function for water conductivity in the studied lakes that can be applied in further palaeoecological studies.     

Diversity and biogeography of the Antarctic flora

Aim To establish how well the terrestrial flora of the Antarctic has been sampled, how well the flora is known, and to determine the major patterns in diversity and biogeography. Location Antarctica south of 60° S, together with the South Sandwich Islands, but excluding South Georgia, Bouvetøya and the periantarctic islands. Methods Plant occurrence data were collated from herbarium specimens and literature records, and assembled into the Antarctic Plant Database. Distributional patterns were analysed using a geographic information system. Biogeographical patterns were determined with a variety of multivariate statistics. Results Plants have been recorded from throughout the Antarctic, including all latitudes between 60° S and 86° S. Species richness declines with latitude along the Antarctic Peninsula, but there was no evidence for a similar cline in Victoria Land and the Transantarctic mountains. Multi‐dimensional scaling ordinations showed that the species compositions of the South Orkney, South Shetland Islands and the north‐western Antarctic Peninsula are very similar to each other, as are the floras of different regions in continental Antarctica. They also suggest, however, that the eastern Antarctic Peninsula flora is more similar to the flora of the southern Antarctic Peninsula than to the continental flora (with which it has traditionally been linked). The South Sandwich Islands have a flora that is very dissimilar to that in all Antarctic regions, probably because of their isolation and volcanic nature. Main conclusions The Antarctic flora has been reasonably well sampled, but certain areas require further floristic surveys. Available data do, however, allow for a number of robust conclusions. A diversity gradient exists along the Antarctic Peninsula, with fewer species (but not fewer higher taxa) at higher latitudes. Multi‐dimensional scaling ordination suggests three major floral provinces within Antarctica: northern maritime, southern maritime, and continental. Patterns of endemism suggest that a proportion of the lichen flora may have an ancient vicariant distribution, while most bryophytes are more recent colonists.     

Ciliate biogeography in Antarctic and Arctic freshwater ecosystems: endemism or global distribution of species?

Ciliate diversity was investigated in situ in freshwater ecosystems of the maritime (South Shetland Islands, mainly Livingston Island, 63 degrees S) and continental Antarctic (Victoria Land, 75 degrees S), and the High Arctic (Svalbard, 79 degrees N). In total, 334 species from 117 genera were identified in both polar regions, i.e. 210 spp. (98 genera) in the Arctic, 120 spp. (73 genera) in the maritime and 59 spp. (41 genera) in the continental Antarctic. Forty-four species (13% of all species) were common to both Arctic and Antarctic freshwater bodies and 19 spp. to both Antarctic areas (12% of all species). Many taxa are cosmopolitans but some, e.g. Stentor and Metopus spp., are not, and over 20% of the taxa found in any one of the three areas are new to science. Cluster analysis revealed that species similarity between different biotopes (soil, moss) within a study area was higher than between similar biotopes in different regions. Distinct differences in the species composition of freshwater and terrestrial communities indicate that most limnetic ciliates are not ubiquitously distributed. These observations and the low congruence in species composition between both polar areas, within Antarctica and between high- and temperate-latitude water bodies, respectively, suggest that long-distance dispersal of limnetic ciliates is restricted and that some species have a limited geographical distribution.     

Surface lithofacies,biofacies, and diatom diversity patterns as models for delineation of climatic change in the southeast Atlantic Ocean

Distribution of diatom species in surface sediments of the southeast Atlantic Ocean is regulated by present-day oceanographic and hydrodynamic processes. Five assemblages (vectors) defined by factor-vector analysis, reflect different environments and conditions. Assemblage A is a high diversity flora associated with the nutrient-rich, relatively cold waters south of the Polar Front in the diatom ooze belt. Occurrence of this flora on Maud Rise and vicinity may reflect periodic occurrence of a polynya in that area. Assemblage B is a reworked assemblage that dominates the southern portion of the study area. Productivity there is low, reflecting sea ice cover during most of the year. The area north of the Polar Front is dominated by Assemblage C, whose characteristic species reflect the relatively warm Subantarctic Surface Water. Winnowing and frustule breakage have altered Assemblage D (found in three isolated samples) by removing relatively delicate forms leaving lag deposits of more robust species. Assemblage E is a low diversity stress flora, reflecting unstable, unpredictable environments along the Polar Front, Antarctic slope, and the northern boundary of winter sea ice. These sites are characterized by the sinking of cold water. Downcore analysis of cores lying adjacent to the Polar Front and the diatom ooze—pelagic clay boundary show evidence for past climatic variation. The low trophic level occupied by diatoms and the subsequent sensitivity of these organisms to abiotic environmental parameters such as light quality, make relative diatom abundance a useful tool for monitoring fluctuations of winter sea ice and the temperature changes responsible for these fluctuations. The position of the Polar Front has migrated at least three times within the last 0.015 m.y. B.P. Within the last 0.3 m.y. B.P. warm maxima have occurred at approximately 0.0, 0.015, 0.125 and 0.3 m.y. B.P.     

Diatom communities from the sub-Antarctic Prince Edward Islands: diversity and distribution patterns

During an extensive survey of the freshwater and moss-inhabiting diatoms of the Prince Edward Islands, a total of 214 taxa belonging to 60 genera were found. Three main communities can be found on the two islands. A large part of the samples was grouped into an aquatic group, bringing together all samples from lentic and lotic waterbodies. A second, contrasting, group was formed by all dry samples whereas in a third group all habitats with higher mineral contents were found. The habitats differed clearly in taxa composition reflecting that way possible environmental differences. Although the diatom composition between the two islands of this island group (Marion and Prince Edward Island) showed some minor qualitative differences, no marked quantitative differences have been observed. The diatom flora shows a distinct similarity with the other islands in the southern Indian Ocean, such as the Crozet archipelago and the Kerguelen Islands forming a biogeographical entity in this part of the ocean, distinctly separated from the non-marine diatom flora in other parts of the (sub-)Antarctic Region.     

The diversity, distribution and ecology of diatoms from Antarctic inland waters

Diatoms are abundant and diverse in many Antarctic freshwaters, with a general trend of decreasing diversity moving southwards. They form an important component of many benthic algal communities in streams and standing waters but are generally less common in the phytoplankton. Diatoms are excellent ecological indicator species and, because their remains are preserved in many sedimentary environments, there appears to be a great potential for palaeoenvironmental reconstruction and the examination of past diversity. A lack of taxonomic precision and consistency, coupled with the insufficient collection from some geographical areas, makes the estimation of the number of Antarctic diatom species problematic.     

Brittle stars from Southern Ocean (Echinodermata: Ophiuroidea)

The present biogeographic study on the ophiuroid fauna from the Southern Ocean (SO) contains an updated checklist, based on a compilation of all the published information provided for the Antarctic and sub-Antarctic regions as well as the information available in SCAR-MarBIN database. Faunal composition and geographical and bathymetric distribution are included. So far, 219 species have been recorded, of which 126 are endemic to the SO, 76 are exclusive to Antarctic waters, and 30 are exclusive to sub-Antarctic waters. This study corroborated the circumpolar and eurybathic character of the ophiuroid fauna of the SO, but some differences are discussed when considering shelf and deep-sea fauna in the whole SO, or in the Antarctic and sub-Antarctic regions separately. The biogeographic affinities of 17 areas considered in the SO are revised, based on a presence/absence datamatrix of the 219 species. This similarity analysis shows three main groups, two of them including sub-Antarctic areas and one for Antarctic areas. The faunal movement patterns between the main geographical connections have been based on historical site records of each species. These movements have a level of faunal exchange that exceeds that of other Antarctic benthic groups. Such movements are mainly from Antarctic and sub-Antarctic regions to the subtropical waters of South America, and from New Zealand and southern Australian waters to sub-Antarctic areas. In this context, the origin of the ophiuroid Antarctic fauna is discussed.     

Characterization of Bacterial,Archaeal and Eukaryote Symbionts from Antarctic Sponges Reveals a High Diversity at a Three-Domain Level and a Particular Signature for This Ecosystem

Sponge-associated microbial communities include members from the three domains of life. In the case of bacteria, they are diverse, host specific and different from the surrounding seawater. However, little is known about the diversity and specificity of Eukarya and Archaea living in association with marine sponges. This knowledge gap is even greater regarding sponges from regions other than temperate and tropical environments. In Antarctica, marine sponges are abundant and important members of the benthos, structuring the Antarctic marine ecosystem. In this study, we used high throughput ribosomal gene sequencing to investigate the three-domain diversity and community composition from eight different Antarctic sponges. Taxonomic identification reveals that they belong to families Acarnidae, Chalinidae, Hymedesmiidae, Hymeniacidonidae, Leucettidae, Microcionidae, and Myxillidae. Our study indicates that there are different diversity and similarity patterns between bacterial/archaeal and eukaryote microbial symbionts from these Antarctic marine sponges, indicating inherent differences in how organisms from different domains establish symbiotic relationships. In general, when considering diversity indices and number of phyla detected, sponge-associated communities are more diverse than the planktonic communities. We conclude that three-domain microbial communities from Antarctic sponges are different from surrounding planktonic communities, expanding previous observations for Bacteria and including the Antarctic environment. Furthermore, we reveal differences in the composition of the sponge associated bacterial assemblages between Antarctic and tropical-temperate environments and the presence of a highly complex microbial eukaryote community, suggesting a particular signature for Antarctic sponges, different to that reported from other ecosystems.     

Regional distribution of diatom assemblages in the headwater streams of Luxembourg

The aim of this study was to determine the influence of environmental variables on the structure of benthic diatom assemblages, and to propose type assemblages of diatoms characterizing unpolluted headwater streams of Luxembourg. A total of 289 diatom samples were collected in the headwater streams of Luxembourg. At each sampling site, physical and chemical variables were also measured. The relationships between environmental variables and the distribution of the taxa were estimated using univariate and multivariate statistical analyses. On the basis of geology and stream water chemistry, Luxembourg could be separated in two regions. The streams in the schistose northern part of Luxembourg presented a low carbonate hardness (median 3.5° F); the streams in the southern part of Luxembourg presented a high carbonate hardness (median 21.8° F) notably connected to the presence of sandstone and limestone substrata. A Twinspan classification carried out on diatom assemblages defined two groups of samples corresponding to these two regions. The carbonate hardness that is related to the nature of the geological substratum appeared to be the major structuring variable for the assemblage composition. Anthropogenic pollution was a secondary structuring variable for diatom assemblages since each group could be subdivided in subgroups presenting statistically different nutrient and organic matter concentrations. The diatom assemblages of these subgroups were characterised by differences of saprobic and trophic preferences. On the basis of these results, two type assemblages of diatoms are proposed for the unpolluted headwater streams in the two regions of Luxembourg. The presence of these different type assemblages in Luxembourg shows the necessity to adapt diatom bioindication to the different regions of the country.     

Diatom, chrysophyte and protozoan distributions along a latitudinal transect in Fennoscandia

Diatoms, chrysophyte scales and cysts, and the siliceous plates of thecoamoebae were studied from the surface sediments of 20 freshwater habitats in Fennoscandia The study sites are distributed along a latitudinal transect extending from southern Finland to northern Norway, spanning boreal forest through arctic tundra vegetational zones Diatom assemblages were usually dominated by acidophilic, periphytic members of the genera Achnanthe, Fragilaria and Navicula Marked shifts in diatom assemblage composition were recorded along the latitudinal transect, whereas scaled chrysophytes were rare in all study sites Meanwhile, siliceous protozoa were common, but did not exhibit any noticeable trends in assemblage composition with changing latitude A comparison of the Fennoscandian diatom assemblages with those recorded from freshwater sites near Yellowknife (central Northwest Territories, Canada) revealed similar trends in diatom assemblage composition with changing ecoclimatic zones in both regions Moreover, canonical correspondence analysis showed that diatom assemblages in cold, dilute tundra sites were effectively separated from sites with forested catchments from both the Fennoscandian and Canadian transects The general similarity between the two regions suggests that autecological data and the resulting environmental transfer functions based on diatom assemblages may eventually be joined from North American and European regions     

Composition and community structure of pelagic copepods in the Indian sector of the Antarctic Ocean during the end of the austral summer

The present paper describes latitudinal and vertical changes in the composition, abundance and diversity of copepods in the Indian sector of the Antarctic Ocean, during the end of austral summer along a transect on 66°30′E between 43 and 62°S, within three layers (600–0, 200–0, 100–0 m). Highest copepod densities were noted in the central part of the transect, between the Antarctic Divergence and the Antarctic Convergence, with a maximum in the Antarctic Divergence zone, particularly in the upper levels of the water column. A total number of 80 copepod species were identified over the entire survey area. The south end and the central part of the transect comprised a small number of species. North of the Antarctic Convergence, this number increased markedly with the progressive disappearence of those species characteristic of Antarctic waters and their replacement by temperate and subtropical species. Generally, small copepods, particularly Oithona similis, Oithona frigida and Ctenocalanus citer, dominated in numbers in both Antarctic and sub-Antarctic areas. The contribution of large species to total copepod numbers was much lower, with Calanus simillimus in the central part of the transect, Pleuromamma borealis in the subtropical zone and Calanus propinquus in the southern part. Correspondence analysis showed a marked latitudinal gradient in population structure with four groups of samples and species corresponding to four latitudinal zones. Community structure (species richness, relative dominance index, evenness, Shannon species diversity index) and species abundance patterns (as rank-frequency diagrams) suggested that the maturity and species richness increased gradually from south to north. A low diversity index and evenness were observed in the area of the Antarctic Divergence, whereas the convergence zone showed high diversity and evenness. Conversely, the frontal zone showed high diversity and evenness. Distribution appeared unrelated to chlorophyll concentrations and on the large scale was related to the hydrologic characteristics. Received: 8 May 1996 / Accepted: 27 August 1996     

Spatiotemporal changes in diatom ecological profiles: implications for biomonitoring

Diatom indices developed in certain geographic regions are frequently used elsewhere, despite the strong evidence that such metrics are less useful when applied in regions other than that where species–environment relationships were originally assessed, showing that species have particular autoecological requirements in different geographic areas. In this study, we define the ecological profiles for selected environmental variables in three common epilithic diatom species in the Duero Basin (NW Spain), comparing our results with data gathered from different geographic regions. We assess differences in autoecological parameters obtained from the northern and southern subbasins, and from different years, in order to observe whether significant small-scale, spatiotemporal changes exist. Our results show that there are variations in species’ autoecological parameters between different regions. Furthermore, there are significant changes comparing northern and southern Duero subbasins for certain species and physiochemical variables. Additionally, different autoecologies have been observed for certain diatoms and environmental factors comparing two different years. It can be concluded that freshwater diatom autoecologies can vary between different geographic areas. This implies that, in order to improve water-quality bioassessments, autoecology-based diatom metrics should be developed by quantifying species distributions along environmental gradients, using datasets representative of the areas or river types where the metrics will be applied.     

Phylogenetic diversity of culturable bacteria from Antarctic sandy intertidal sediments

The diversity of culturable bacteria associated with sandy intertidal sediments from the coastal regions of the Chinese Antarctic Zhongshan Station on the Larsemann Hills (Princess Elizabeth Land, East Antarctica) was investigated. A total of 65 aerobic heterotrophic bacterial strains were isolated at 4°C. Microscopy and 16S rRNA gene sequence analysis indicated that the isolates were dominated by Gram-negative bacteria, while only 16 Gram-positive strains were isolated. The bacterial isolates fell in five phylogenetic groups: Alpha- and Gammaproteobacteria, Bacteroidetes, Actinobacteria and Firmicutes. Based on phylogenetic trees, all the 65 isolates were sorted into 29 main clusters, corresponding to at least 29 different genera. Based on sequence analysis (<98% sequence similarity), the Antarctic isolates belonged to at least 37 different bacterial species, and 14 of the 37 bacterial species (37.8%) represented potentially novel taxa. These results indicated a high culturable diversity within the bacterial community of the Antarctic sandy intertidal sediments.     

Diatoms are better indicators of urban stream conditions: A case study in Beijing,China

Urbanization dramatically affects hydrology, water quality and aquatic ecosystem composition. Here we characterized changes in diatom assemblages along an urban-to-rural gradient to assess impacts of urbanization on stream conditions in Beijing, China. Diatoms, water chemistry, and physical variables were measured at 22 urban (6 in upstream and 16 in downstream) and 7 rural reference stream sites during July and August of 2013. One-way ANOVA showed that water physical and chemical variables were significantly different (p < 0.05) between urban downstream and both reference and urban upstream sites, but not between reference and urban upstream sites (p > 0.05). Similarly, structural metrics, including species richness (S), Shannon diversity (H′), species evenness (J′) and Simpson diversity (D′), were significantly different (p < 0.05) between urban downstream and both reference and urban upstream sites, but not (p > 0.05) between reference and urban upstream sites. However, diatom assemblages were very different among all sites. Achnanthidium minutissima was a consistent dominant species in reference sites; Staurosira construens var. venter and Pseudostaurosira brevistriata were the dominant species in urban upstream sites; and Nitzschia palea was the dominant species in urban downstream sites. Clustering analyses based on the relative abundance of diatom species, showed all the samples fit into three groups: reference sites, urban upstream sites, and urban downstream sites. Canonical correspondence analysis (CCA) and Monte Carlo permutation tests showed that concentration of K⁺, EC, TN, Cl⁻ and pH were positively correlated with relative abundance of dominant diatom species in urban downstream samples; WT and F⁻ were correlated with reference and urban stream diatom composition. Our results demonstrate that the composition of diatom species was more sensitive to urbanization than the water physical and chemical parameters, and that diatom assemblage structure metrics more accurately assessed water quality. Some species, such as Amphora pediculus and Cocconeis placentula were among the dominant species in low nutrients stream sites; however, they were considered to be high nutrient indicators in some streams in USA. We suggest using caution in applying indicator indices based on species composition from other regions. It is necessary to build a complete set of diatom species data and their co-ordinate environment data for specific regions.     

The development of planktonic biogeography in the Southern Ocean during the Cenozoic

Deep-sea drilling at high latitudes of the Southern Hemispheres has provided almost the only available data to evaluate the biogeographic development of the planktonic biota in the Southern Ocean during the Cenozoic (65 m.y. to Present Day). Paleontological investigations on Deep Sea Drilling Project (DSDP) materials have shown that the development of Cenozoic planktonic biogeography of the Southern Ocean is intimately linked with the evolution of the Southern Ocean water masses themselves. During the Cenozoic, this has included the development of the Circum-Antarctic Current system as obstructing land masses moved apart, the refrigeration and later extensive glaciation of the continent, and the development of the Antarctic Convergence (Polar Front) with related oceanic upwelling.Almost all evolution of calcareous planktonic microfossils has occurred outside of the Antarctic—Subantarctic region followed by limited migration into these water masses. Virtually no endemism occurs amongst calcareous microfossil groups at these latitudes. In contrast, conspicuous and widespread evolution has occurred within the siliceous microfossil groups especially during the Neogene. Low diversity and differences in stratigraphic ranges of Antarctic calcareous microfossils makes them only broadly useful for correlation. Relatively higher diversities within the Subantarctic provide a firmer basis for more detailed correlation, although the ranges of fossils are often different than at lower latitudes because of different paleoceanographic and paleoclimatic controls. Within the Antarctic water mass south of the Antarctic Convergence, siliceous microfossilsbiostratigraphy, oxygen isotopic stratigraphy and magnetostratigraphy, provide the only firm basis for correlation with low-latitude sequences.Eocene (55-38 Ma) sediments contain abundant calcareous microfossils even closely adjacent to the continent. Antarctic calcareous planktonic microfossils of this age exhibit relative high diversity, although this is lower than assemblages of equivalent age at middle and low latitudes. Within the Subantarctic region, Eocene planktonic foraminifera exhibit strong affinities with those in the temperate regions. Biogeographic differences exist between various sectors of the Southern Ocean related to biogeographic isolation preceding the development of the Circum-Antarctic Current. Subantarctic calcareous nannofossil assemblages of Paleocene and Eocene age exhibit higher diversity than Oligocene and Neogene assemblages. Siliceous microfossils are poorly represented or at best poorly known.One of the most dramatic changes in Southern Ocean planktonic biogeography occurred near the Eocene/Oligocene boundary (38 Ma). Since then, Antarctic planktonic foraminiferal assemblages have exhibited distinct polar characteristics, marked in particular by low diversity, and this event thus reflects the initiation of the Antarctic faunal and floral provinces. Profound paleoceanographic changes at this time, which triggered the biogeographic crisis, appear to be related to the initiation of widespread Antarctic sea-ice formation, and rapid cooling of deep and intermediate waters, in turn associated with increased Antarctic glaciation. During the Oligocene, planktonic microfossil diversity was low in all groups throughout the world's oceans. In Antarctic waters, the early Oligocene foraminiferal fauna is monospecific (Subbotina angiporoides), while in the later Oligocene two species (S. angiporoides and Catapsydrax dissimilis) were recorded. Calcareous nannofossil assemblages are of low diversity compared with the Eocene. Subantarctic foraminiferal faunas of Oligocene age display much higher diversity than those in the Antarctic, but early and middle Oligoceae faunas still exhibit the lowest diversities for the entire Cenozoic. Siliceous assemblages remain relatively inconspicuous in most regions of the Southern Ocean.The Paleogene-Neogene transition (22 Ma) is marked by a major change in the global planktonic biogeography, i.e. modern patterns developed in which permanent, steep faunal and floral diversity gradients existed between tropical and polar regions; a gradient which has persisted even during the most severe glacial episodes. Oligocene assemblages of low diversity and almost cosmopolitan distribution were replaced by distinctive belts of planktonic assemblages arranged latitudinally from the tropics to the poles. The establishment of the steep planktonic diversity gradients and latitudinal provinces near the beginning of the Neogene almost certainly were linked to the development of the Circum-Antarctic Current in the late Oligocene which effectively separated high- and low-latitude planktonic assemblages. These fundamental global circulation and biogeographic patterns have persisted through the Neogene.During the Neogene (22 Ma to Present Day), Antarctic calcareous microfossil assemblages exhibit persistent low diversity and high dominance, while Subantarctic assemblages are of much greater diversity. The beginning of the Neogene (= beginning of Miocene) heralded the development of the high-latitude siliceous microfossil assemblages towards their present-day dominant role. Siliceous biogenec productivity began to increase. These changes were linked to the initial development and later intensification of circulation associated with the Antarctic Convergence and Antarctic Divergence. The Antarctic Convergence sharply separates dominantly siliceous assemblages to the south from calcareous assemblages to the north. Radiolarian assemblages became more endemic. Relatively warm early and middle Miocene conditions are reflected by slightly higher diversity of planktonic foraminifera and by the presence, in the northern Subantarctic, of conspicuous discoasters in early Miocene sediments. In Antarctic waters, calcareous nannofossils become unimportant as biogenic elements after the middle Miocene.The latest Miocene ( 5 m.y. ago) was marked by northward movement of the Antarctic Convergence, corresponding expansion of the Antarctic water mass, and low diversity of calcareous assemblages. Pliocene planktonic foraminifera seem to be largely monospecific in Antarctic and southern Subantarctic sequences. During the Quaternary, Antarctic waters reached a maximum northward expansion and exhibit highest siliceous biogenic productivity for the Cenozoic. In the Subantarctic, Quaternary foraminiferal diversities are much higher than in Pliocene sequences. Although calcareous nannofossil diversity may be high, only a few species are abundant. Large northward shifts of Antarctic and Subantarctic water masses have occurred during the Quaternary although no southward penetrations have occurred much beyond that of the present day. Several radiolarian and foraminiferal species disappeared or appeared at or close to a number of paleomagnetic reversals during the last 4 m.y. These faunal events, which provide valuable datums, do not seem to be associated with major climatic changes.     

Local environment rather than past climate determines community composition of mountain stream macroinvertebrates across Europe

Community assembly is determined by a combination of historical events and contemporary processes that are difficult to disentangle, but eco‐evolutionary mechanisms may be uncovered by the joint analysis of species and genetic diversity across multiple sites. Mountain streams across Europe harbour highly diverse macroinvertebrate communities whose composition and turnover (replacement of taxa) among sites and regions remain poorly known. We studied whole‐community biodiversity within and among six mountain regions along a latitudinal transect from Morocco to Scandinavia at three levels of taxonomic hierarchy: genus, species and haplotypes. Using DNA barcoding of four insect families (>3100 individuals, 118 species) across 62 streams, we found that measures of local and regional diversity and intraregional turnover generally declined slightly towards northern latitudes. However, at all hierarchical levels we found complete (haplotype) or high (species, genus) turnover among regions (and even among sites within regions), which counters the expectations of Pleistocene postglacial northward expansion from southern refugia. Species distributions were mostly correlated with environmental conditions, suggesting a strong role of lineage‐ or species‐specific traits in determining local and latitudinal community composition, lineage diversification and phylogenetic community structure (e.g., loss of Coleoptera, but not Ephemeroptera, at northern sites). High intraspecific genetic structure within regions, even in northernmost sites, reflects species‐specific dispersal and demographic histories and indicates postglacial migration from geographically scattered refugia, rather than from only southern areas. Overall, patterns were not strongly concordant across hierarchical levels, but consistent with the overriding influence of environmental factors determining community composition at the species and genus levels.     

四川夹金山小型兽类区系及多样性

夹金山位于西南山地,是近年来生物多样性研究的热点地区,我们对其不同海拔和不同生境类型的小型兽类进行了调查,共捕获927 号个体,隶属4 目8 科35 种,其中啮齿类16 种,食虫类16 种,鼠兔类有3 种。数据分析显示:(1) 因南北气候差异,夹金山南坡物种(31)显著高于北坡(20);(2)在35 个物种中,中国特有种高达15 种,同样,该地区食虫类具有较高物种多样性;(3)北坡古北界成分显著高于南坡古北界成分,夹金山在一定程度上限制了古北界和东洋界物种的南北交流;(4)南坡小型兽类物种多样性最高见于中海拔区域(2 400 ～ 3 000 m),低海拔区域人类干扰严重,高海拔区域植被类型单一,然而北坡由于低海拔区域气候干旱,多样性最高的海拔区域(3 000 ～ 3 600 m)呈现上移。夹金山内复杂的地形有助于物种分化,并为小型兽类提供了多样化的栖息生境。因此,该地区特有种和物种多样性较丰富。该区域内具丰富的食虫类物种,其原因可能是食虫类具有较多的进化优势.     

PERIPHYTIC DIATOM ASSEMBLAGES FROM ULTRA‐OLIGOTROPHIC AND UV TRANSPARENT LAKES AND PONDS ON VICTORIA ISLAND AND COMPARISONS WITH OTHER DIATOM SURVEYS IN THE CANADIAN ARCTIC1

Periphytic diatoms are potentially powerful indicators of environmental change in climatically‐sensitive high latitude regions. However, only a few studies have examined their taxonomic and ecological characteristics. We identified and enumerated diatom assemblages from sediment, rock, and moss habitats in 34 ultra‐oligotrophic and highly transparent lakes and ponds on Victoria Island, Arctic Canada. The similar limnological characteristics of the sites allowed us to examine the influence of habitat, independent of water chemistry, on the diatom assemblages. As is typical in shallow arctic water bodies, benthic taxa, including species of Achnanthes, Caloneis, Cymbella, Navicula, and Nitzschia, were most widely represented. Minor gradients in our measured environmental variables did not significantly explain any variance in diatom species, but there were marked differences in diatom assemblages among sites. Pond ephemerality seems to explain some diatom variation, because aerophilic taxa such as Achnanthes kryophila Petersen and A. marginulata Grunow were dominant in shallow sites that had undergone appreciable reductions in volume. We identified several taxa that exhibited strong habitat preferences to sediment, moss, or rock substrates and also found significant differences (P < 0.01) in diatom composition among the three habitats. In comparisons with three similar diatom surveys extending over 1200 km of latitude, we determined that surface sediment assemblages differed significantly (P < 0.001) among all regions examined. Diatom species diversity was inversely related to latitude, a result likely explained by differences in the lengths of growing seasons. These data contribute important ecological information on diatom assemblages in arctic regions and will aid in the interpretation of environmental changes in biomonitoring and paleolimnological studies.