Distribution of cladoceran assemblages across environmental gradients in Nova Scotia (Canada) lakes

Cladocera sub-fossils have widely been recognized as useful environmental indicators. Nevertheless, investigations into the distribution and environmental controls on Cladocera are scarce in North America, hindering their use in paleolimnological studies. Here, we examine cladoceran assemblage and size structure from the surface sediments of 49 soft-water Nova Scotia (Canada) lakes to provide ecological data on this key taxonomic group, the first study of its kind for the northern Atlantic coast of North America. We found that Nova Scotia lakes contain a diverse chydorid assemblage, but were generally dominated by the smaller pelagic herbivore Eubosmina longispina. Daphnia, a larger pelagic herbivore, was relatively uncommon in these lakes. Redundancy analyses (RDA) identified maximum lake depth and dissolved organic carbon (DOC) as the environmental variables that best explained the structuring of these cladoceran assemblages. Generalized linear models were then used to better characterize the ecological associations for individual taxa. Body size of the bosminids in these lakes was significantly correlated only to total nitrogen (TN), with larger bosminids in lakes with lower TN values. Bosminid mucro length, an indication of invertebrate and fish predation pressure, was significantly related to TN, maximum lake depth, and lake surface area. The ecological information provided by this study should assist the interpretation of paleolimnological assessments of environmental change in these and other similar lakes.     

The effect of local anthropogenic habitat heterogeneity on assemblages of carabids (Coleoptera,Caraboidea) endemic to the Alps

We assessed the response of a guild of endemic medium and large-bodied carabid species to the local (fine-grained) habitat heterogeneity induced by man. The study was conducted by means of trapping (without killing and preservative agents) and radio-tracking methods (to collect data on the spatial ecology of the endangered species Carabus olympiae Sella). Habitat differentiation induced by man (a mosaic of beech forests, alpen rose shrubberies and pastures) affected species richness and abundance of the guild, which were significantly higher in forests and/or shrubberies than in pastures. Most species preferred forests and shrubberies, with the only exception of Carabus concolor Fabricius, which preferred open areas. Species distribution was also affected by stone density and cattle grazing intensity. In particular, petrophilous species peaked on the roadside because of the high stone density there (stones amassed during road construction), while species abundances significantly lowered in overgrazed pastures. The compactness of the paths made by C. olympiae individuals (evaluated through a tortuosity index) was significantly higher in beech forests than in alpen rose shrubberies, indicating movements in the latter habitat type were bound by the spatial distribution of shrubs, which imposes a limit on path tortuosity. Our findings suggest that local ground beetle species diversity strongly depends on small-scale anthropogenic variables (namely habitat type, stone density and grazing intensity), and that habitat modifications (namely from forest to shrubbery) may significantly affect species movement patterns. General and local conservation management suggestions are given in conformity with these results.     

The quantification of local substrate heterogeneity in streams and its significance for macroinvertebrate assemblages

The effect of substrate heterogeneity on the structure of stream macroinvertebrate assemblages (total abundance, taxon richness, and evenness) is still not clear, but this could be due to the lack of standard methods for quantifying substrate heterogeneity. An accurate quantification of substrate heterogeneity was obtained from photographs of sampled areas (each 225 cm²), which were used to create maps that were subsequently digitized and analyzed using image analysis software. These maps allowed the calculation of multiple metrics quantifying two aspects of substrate heterogeneity: composition and spatial configuration of substrate patches. The diversity of substrate types (calculated as the Shannon diversity index), and the heterogeneity of patch compactness (calculated as the coefficient of variation of the relationship between patch dimensions) were the metrics explaining more biotic variance at the sample scale, but at higher scales there were no relationships between assemblage structure and substrate heterogeneity. Most variation in substrate heterogeneity occurred at the sample scale, while some metrics varied significantly at riffle or segment scales; these patterns of variation match those of macroinvertebrate assemblages, which had been previously studied. The importance of quantifying substrate heterogeneity and considering the spatial scales of its study are discussed.     

Regional enrichment of local assemblages is robust to variation in local productivity, abiotic gradients, and heterogeneity

Theory predicts that the effects of regional richness on the richness of local communities may depend on the productivity, resource availability, and/or heterogeneity of local sites. Using the wetland plant communities of 50 independent streams as 'regions', we tested whether: (1) local richness in 1-m² quadrats and 50-m stream segments was positively related to regional richness, even after environmental influences were considered; and (2) the effect of regional richness would interact with the effects of biomass, soil moisture, and/or heterogeneity on local richness. In models that explained up to 88% of variation in local richness, we found that richness at both local scales was positively related to regional richness, and that regional richness did not interact with any of the environmental gradients that also shaped local richness. We conclude that species availability from the regional pool may consistently enrich local communities, even while other constraints on local richness operate.     

The artificial infection of the cladoceran Moina macrocopa (Crustacea: Phyllopoda) with the microsporidia Gurleya sp. (Microsporidia: Gurleyidae)

Microcrustaceans Moina macrocopa (Straus, 1820) have been collected in a small vernal pond and cultured under laboratory conditions. The infection of this culture with the microsporidia Gurleya sp. was detected and high virulence of this microsporidian species allowed us to carry out the transmission experiments. Horizontal transmission, the high host specificity and maximal spore production in the hypodermal and fat body cells through 5-6 days after per oral experimental infection have been revealed. Histological investigations demonstrated that Gurleya sp. reduces drastically host reproductive success without a considerable influence on the microcrustaceans' mortality.     

Alona stochi n.sp. – the third cave-dwelling cladoceran (Crustacea: Cladocera) from the Dinaric region

Nemerteans (phylum Nemertea) have been viewed by mostzoologists as descended from, or closely related to,the flatworms. This view is based mainly on theirsupposedly acoelomate body. Their ancestry, however,is a point of controversy and there is evidence for acoelomate, protostomous origin. Notwithstanding thesedifferent views, most zoologists consider nemerteansto be phylogenetically distant from the chordates.Four authors (Hubrecht, Macfarlane, Jensen, Willmer),however, have postulated that nemerteans instead areclosely related to the chordates and that they sharea most recent common ancestor with the vertebrates. We argue that this view is based on a flawed view ofhomology and of seeing evolution as a series ofprogressions, which has no support in modernevolutionary thinking. Since there are nomorphological synapomorphies supporting aChordata-Nemertea clade, these authors instead guesswhat characteristics in extant nemerteans gave rise tocharacters observed in recent chordates. For example,they propose that the nemertean proboscis sheath hasevolved into the notochord. This is mere speculation,lacking testable propositions and is hence void ofinformation, and thus becomes futile in our view. However, the idea of a nemertean-vertebrate sisterrelationship as such is a testable hypotheses, and wetest it by applying the parsimony criterion to a setof morphological characters, and a set of molecular(the 18S rRNA gene) characters. Both tests reject thehypothesis.     

New data on crinoid assemblages from the oldest sedimentary rocks of the Polish Outer Carpathians (Jurassic-Cretaceous)

Crinoids (Crinoidea) preserved in the so-called Cieszyn Beds (Tithonian-Hauterivian; southern Poland) are relatively numerous, especially in some levels, but not highly diversified. They are absent in the Lower Cieszyn Shale (Tithonian) and the Upper Cieszyn Shale (Valanginian-Hauterivian). The Lower Cieszyn Limestone (Tithonian) yielded crinoid remains classified as Isocrinus cf. amblyscalaris (Thurmann) and Isocrinida indet. In the Upper Cieszyn Limestone (Berriasian) crinoids are much more numerous and diversified. The following taxa are recorded: Isocrinus? annulatus (Roemer), Balanocrinus subteres (Münster), B. cf. smithi Hess and Gale, and Hemicrinus sp. The presence of specimens resembling Isocrinus amblyscalaris (Thurmann) in the Tithonian strata is surprising since the last occurrence of this taxon was reported from the Kimmeridgian. The Lower Cieszyn Limestone crinoidal assemblage is dominated by isocrinids (Isocrinida). This probably reflects the much shallower sedimentary environment of these sediments compared to that of the Upper Cieszyn Limestone, where excepting isocrinids, hemicrinids (Hemicrinidae, Cyrtocrinida) typical for deep marine environments were found. It is consistent with the analytical results from the foraminiferal assemblages, among which the benthic forms known from shelfal and paralic epicontinental environments first dominated, and then were supplanted by deep-sea taxa at the turn of the Jurassic and Cretaceous.     

The noncosmopolitanism paradigm of freshwater zooplankton: insights from the global phylogeography of the predatory cladoceran Polyphemus pediculus (Linnaeus, 1761) (Crustacea,Onychopoda)

A major question in our understanding of eukaryotic biodiversity is whether small bodied taxa have cosmopolitan distributions or consist of geographically localized cryptic taxa. Here, we explore the global phylogeography of the freshwater cladoceran Polyphemus pediculus (Linnaeus, 1761) (Crustacea, Onychopoda) using two mitochondrial genes, cytochrome c oxidase subunit I and 16s ribosomal RNA, and one nuclear marker, 18s ribosomal RNA. The results of neighbour‐joining and Bayesian phylogenetic analyses reveal an exceptionally pronounced genetic structure at both inter‐ and intra‐continental scales. The presence of well‐supported, deeply divergent phylogroups across the Holarctic suggests that P. pediculus represents an assemblage of at least nine, largely allopatric cryptic species. Interestingly, all phylogenetic analyses support the reciprocal paraphyly of Nearctic and Palaearctic clades. Bayesian inference of ancestral distributions suggests that P. pediculus originated in North America or East Asia and that European lineages of Polyphemus were established by subsequent intercontinental dispersal events from North America. Japan and the Russian Far East harbour exceptionally high levels of genetic diversity at both regional and local scales. In contrast, little genetic subdivision is apparent across the formerly glaciated regions of Europe and North America, areas that historical demographic analyses suggest that were recolonized just 5500–24 000 years ago.     

Chydorid assemblages in the sedimentary sequence of Lake La Cruz (Spain) subject to water level changes

Changes among chydorid assemblages in Lake La Cruzsediments, from a core of 178 cm length, have beenstudied using community structure indices andmultivariate methods (cluster analysis, principalcomponents analysis).The results revealed the existence of two main sourcesof variation in these assemblages. One (axis I ofPCA1) is associated with the trophic level of thelake, which is hypothetised to be greater in thebottom and upper part of the core. Both zones arecharacterised by an increase in the relative frequencyof Chydorus sphaericus, accompanied by a markedreduction in the relative frequency of the mostabundant species throughout the history of the lake,Acroperus neglectus.The other source of variation (axis II of PCA1) may beinterpreted as the alternation of periods of dryer and wetter weather. Ouranalyses show the separation of two assemblages whichalternatively prevail in the sedimentary sequence, oneconstituted by Pleuroxus laevis, Alona guttata,Graptoleberis testudinaria and, sometimes, Alonarectangula, and another dominated by Chydorussphaericus, Alona quadrangularis, Alona affinis andsometimes Leydigia species. According to theecological preferences of these species, the dominanceof the first chydorid assemblage can be related toepisodes of higher temperature and with very low andfluctuating water level, or with a high water levelbut a very reduced extent of shallow water in thelake. Prevalence of the second group corresponds toepisodes with a colder environment and permanentwaters, the level of which could be variable but insuch a way that a benthic sublittoral zone maydevelop. The structure of the community is stronglyaffected by changes in lake level. High indices offluctuation in community structure and small mean bodysize of the chydorid assemblage marked the period withmore extreme dry conditions, characterised by Alona rectangula maxima. The peaks of C. sphaericuscoincided with peaks of the index offluctuation D₀ and prevalence of smaller speciesof the chydorid assemblage.     

浅水湖泊表层沉积物记录的枝角类群落空间分布特征

浅水湖泊污染负荷能力较低,对环境变化敏感,过度开发会导致生态功能明显退化甚至发生稳态转变.本研究通过提取云南18个浅水湖泊的表层沉积物枝角类信息,识别枝角类群落的空间分布特征并甄别其群落构建的环境驱动因子.结果表明:表层沉积物枝角类群落的地理分布存在显著的空间差异,滇西北的枝角类群落以底栖物种占绝对优势,而随着营养水平的增加,滇东南湖泊枝角类优势物种由底栖型向浮游型转变.统计分析表明,海拔和水体总磷水平是驱动群落分布空间差异的关键环境因子,分别独立解释了枝角类群落变化的22.0%和7.7%,反映了海拔梯度及其指示的气候环境过程是控制枝角类群落空间分布的重要因子.同时枝角类群落随营养水平的变化出现差异性的结构特征,可能指示了流域开发、污染物输入、水生植被变化等人类活动扰动的综合影响.同时,海拔和总磷水平表现出显著的相互作用并解释了枝角类群落变化的26.3%,指示了云南地区的人类活动强度随着海拔梯度呈现显著的空间差异,并通过营养盐输入等过程调控了枝角类群落的结构特征.     

Environmental heterogeneity,not distance,structures montane epigaeic spider assemblages in north-western Patagonia (Argentina)

There is considerable controversy around the patterns and processes that influence spatial variation in taxonomic composition in mountain environments. We analysed elevational variation in the taxonomic composition of epigaeic spider assemblages across five mountains in north-western Patagonia (Argentina) to examine the relative importance of dispersal (distance) limitation and environmental heterogeneity on a regional scale. The distance limitation hypothesis predicts greater taxonomic similarity between sampling sites separated by short geographical distances than between mountain peaks separated by longer distances, a lack of indicator species of macro-habitats, and weak associations between spider species composition and environmental gradients. Alternatively, the environmental heterogeneity hypothesis predicts that taxonomic differentiation will occur over short distances along elevation gradients in association with the turnover in major habitats and change in environmental conditions, and that indicator species will be present. We collected spiders using 486 pitfall traps arranged in fifty-four 100-m² grid plots of nine traps separated by ~?100 m of elevation, from the base to the summit of each mountain. Multivariate analyses identified spider assemblages that were associated with macro-habitats rather than with mountains. Local environmental variation (mainly in vegetation cover), precipitation and soil characteristics influenced the spatial variation in species composition. Characteristic indicator species showed high specificity and fidelity to macro-habitats, whereas vulnerable species showed high specificity and low fidelity to mountains or macro-habitats. We conclude that, on a regional scale, species adaptation to environmental gradients plays a more important role than dispersal limitation in structuring the taxonomic composition of spider assemblages. Moreover, the presence of indicator species suggests that spiders have a great potential as ecological indicators for evaluating the response of montane biodiversity to future climatic change.     

Cladocera (Crustacea) from Nicaragua

Thirty-one Cladocera taxa are recorded from lakes, rivers and ponds of Western Nicaragua. They include Alona bromelicola sp. nov. found in water accumulations in epiphytic Bromeliads. The Cladocera recorded are neotropical and circumtropical. Other invertebrates found are also listed.     

Seasonal dynamics and composition of cladoceran and copepod assemblages in ponds of a Hungarian cutaway peatland

Seasonal dynamics of cladoceran and copepod zooplankton were studied over a one‐year period in five permanent ponds of a cutaway peatland, situated in the Danube−Tisza Interfluve, Central Hungary. 17 cladoceran, 11 cyclopoid copepod and 6 harpacticoid copepod species were identified and most of them were typical of small lowland ponds. Nevertheless, some taxa like Cyclops insignis, Ceriodaphnia setosa and Macrocyclops distinctus are considered to be rare in Hungary. The microcrustacean assemblages exhibited apparent seasonal succession with typical seasonal species. There appears to be at least two main successional patterns in the five ponds. After general cyclopoid copepod dominance in winter (Cyclops strenuus and Cyclops insignis), at sites with higher proportion of open water and submerged vegetation, spring was characterized by the dominance of the large cladoceran Daphnia curvirostris, which declined during summer, when microcrustacean assemblages composed mainly of smaller, littoral cladocerans. At these sites, species richness and diversity reached their maximum in autumn. In the case of duckweed covered ponds, succession led to less diverse autumn assemblages with fewer species, dominated by Simocephalus exspinosus. Our results draw the attention to the importance of long‐term investigations and the often neglected winter sampling in the accurate evaluation of species richness (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Environmental calcium and mitochondrial DNA polymorphism among local populations of Gammarus fossarum (Crustacea, Amphipoda)

Mitochondrial DNA sequence analysis was used to investigate genetic diversity and phylogeographic population structure among geographically isolated alpine populations of the amphipod Gammarus fossarum. This study was performed across a region with an important glacial history and substantial geographical variations in calcium levels, in order to evaluate the relative impact on the genetic diversity of the population history and this environmental factor known to be associated with local adaptation and population growth. Analysis of the nucleotide sequences for a 376-bp segment of the cytochrome c oxidase I gene in 84 specimens from seven different populations revealed 20 different haplotypes distributed into five major lineages that are not geographically structured. Analysis of molecular variance indicates that the populations from the crystalline massif are less diverse than those living on limestone, suggesting a global correlation between genetic diversity and calcium concentration of the water. However, the role of this environmental factor appears to be indirect, with smaller population size leading to lower genetic diversity.     

Zooplankton (Cladocera) in assessments of biologic integrity and reference conditions: application of sedimentary assemblages from shallow boreal lakes

Zooplankton are potentially powerful proxies for the assessments of biologic integrity. The paleolimnological perspective and use of fossil Cladocera also provide the means to reconstruct reference conditions and natural long-term community dynamics. Unfortunately, the use of zooplankton in lake quality assessments is currently underexploited. We studied a surface sediment dataset of 41 lakes in Finland to examine the relationship between Cladocera remains and environmental variables. Of the examined environmental variables, total phosphorus availability was found to be the most important variable in explaining the Cladocera community composition. Following the tests on species environment relations, we selected a lake trophic typology as the most suitable environmental variable for developing a new tool for limnoecological quality assessments. A test of the model on a modern and historic sample from a eutrophied lake showed that the test lake has proceeded from “mesotrophic/poor” to “eutrophic/bad” limnoecological state in agreement with previous independent evidence. The model developed here showed favorable performance that can be used to provide reliable estimates of ecological and environmental state of lakes.     

Phylogenetic analysis of Remipedia (Crustacea)

We present a cladistic analysis of the crustacean class Remipedia, including all 17 extant species currently assigned to the order Nectiopoda, with the Carboniferous fossil Tesnusocaris serving as an outgroup. We applied different methodological approaches and coding options to a basic matrix composed of 26 morphological characters. Our analyses strongly support monophyly of the Godzilliidae and affirm justification of the family Micropacteridae. However, the present taxonomic structure within the Speleonectidae is partly incompatible with our results, and we cannot exclude that the family is paraphyletic.     

Benthic predators and zooplanktonic prey: predation by Crangonyx shoemakeri (Crustacea; Amphipoda) on Daphnia obtusa (Crustacea; Cladocera)

Amphipods and cladocerans are common inhabitants of seasonal ponds throughout North America. Although amphipods are usually considered to be benthic detritivores, Crangonyx shoemakeri was found to capture and consume mosquito larvae and Daphnia obtusa. The rate of capture of Daphnia was independent of the amount of decomposing leaf matter available. However, this rate was dependent on prey density and the presence of light, indicating that these amphipods are visual predators.     

Australian Iphimediidae (Crustacea: Amphipoda)

Australian species of the iphimediid amphipod genus Iphimedia are revised. Based on new material from inshore and continental shelf habitats six new species are described: Iphimedia beesleyae; I. filmersankeyi; I. kateae; I. lisae; I. neuweileri and I. oetkeri. Four established species are redescribed: I. ambigua Haswell, 1879; I. discreta Stebbing, 1910; I. edgari (Moore, 1981) and I. warraina (Thomas and Barnard, 1991). A key to Australian species of Iphimedia is provided. Full article published online at http://www.senckenberg.de/odes/06-09.htm