Variability in exchange of CO2 across 12 northern peatland and tundra sites

Many wetland ecosystems such as peatlands and wet tundra hold large amounts of organic carbon (C) in their soils, and are thus important in the terrestrial C cycle. We have synthesized data on the carbon dioxide (CO₂) exchange obtained from eddy covariance measurements from 12 wetland sites, covering 1–7 years at each site, across Europe and North America, ranging from ombrotrophic and minerotrophic peatlands to wet tundra ecosystems, spanning temperate to arctic climate zones. The average summertime net ecosystem exchange of CO₂ (NEE) was highly variable between sites. However, all sites with complete annual datasets, seven in total, acted as annual net sinks for atmospheric CO₂. To evaluate the influence of gross primary production (GPP) and ecosystem respiration (R_eco) on NEE, we first removed the artificial correlation emanating from the method of partitioning NEE into GPP and R_eco. After this correction neither R_eco (P= 0.162) nor GPP (P= 0.110) correlated significantly with NEE on an annual basis. Spatial variation in annual and summertime R_eco was associated with growing season period, air temperature, growing degree days, normalized difference vegetation index and vapour pressure deficit. GPP showed weaker correlations with environmental variables as compared with R_eco, the exception being leaf area index (LAI), which correlated with both GPP and NEE, but not with R_eco. Length of growing season period was found to be the most important variable describing the spatial variation in summertime GPP and R_eco; global warming will thus cause these components to increase. Annual GPP and NEE correlated significantly with LAI and pH, thus, in order to predict wetland C exchange, differences in ecosystem structure such as leaf area and biomass as well as nutritional status must be taken into account.     

Latitudinal gradients and the shaping of life‐history traits in a gregarious caterpillar

The present study aimed to investigate how the impact of several factors linked to geography would shape life‐history traits in a gregarious species, using the pine processionary moth (PPM) Thaumetopoea pityocampa as a model system. PPM has a wide geographical distribution over the Mediterranean Basin, and it is a strictly gregarious species throughout larval development, where the total reproductive output of each female forms a colony. We reviewed both published and unpublished data on PPM from all over its distribution in the Mediterranean Basin and extracted data on fecundity, egg size, egg parasitoid mortality, flight period, and development time. These life‐history traits were then related to location, expressed as latitude and altitude, local average temperatures, and host tree species. We found that PPM fecundity increaseed with latitude, concomitant with an increase in the length of development and an earlier onset of adult flight. These results are the opposite of that found in other Lepidoptera species with a wide geographical distribution, as well as in insects in general. We propose that a large colony size in PPM is important at higher latitudes because this confers an advantage for thermoregulation and tent building in areas where larvae have to face harsher conditions during the winter, thus shifting the optimal trade‐off between the number and size of eggs with latitude. However, host tree species also affected the relationship between egg number and size and the optimal outcome of these traits is likely a compromise between different selection pressures. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 224–236.     

An ecosystem-level perspective of allelopathy

Allelopathy is an interference mechanism by which plants release chemicals which affect other plants; while it has often been proposed as a mechanism for influencing plant populations and communities, its acceptance by plant ecologists has been limited because of methodological problems as well as difficulties of relating the results of bioassays used for testing allelopathy to vegetation patterns in the field. Here we argue that the concept of allelopathy is more appropriately applied at the ecosystem-level, rather than the traditional population/community level of resolution. Firstly, we consider the wide ranging effects of secondary metabolites (widely regarded as allelochemicals) on organisms and processes which regulate ecosystem function, including herbivory, decomposition and nutrient mineralization. It is apparent that plants with allelopathic potential against other organisms induce net changes in ecosystem properties, which may in turn impact upon the plant community in the longer term. We then illustrate these concepts using two contrasting examples of how invasive plant species with allelopathic potential may alter ecosystem properties through the production of secondary metabolites, i.e. Carduus nutans (nodding thistle) in New Zealand pastures and Empetrum hermaphroditum (crowberry) in Swedish boreal forests. In both cases the production of secondary metabolites by the invasive species induces important effects on other organisms and key processes, which help determine how the ecosystem functions and ultimately the structure of the plant community. These examples help demonstrate that the concept of allelopathy is most effectively applied at the ecosystem-level of resolution, rather than at the population-level (i.e. plant-plant interference).     

A demographic comparison of two Nordic populations of Greylag Geese Anser anser

Greylag Geese Anser anser have been neck-banded on an annual basis in Scania, southern Sweden since 1984 and in Norway since 1986 as part of a Nordic Greylag project. This has yielded a large database of resightings, which we used here to estimate and compare survival rates between the two populations by means of mark–recapture models. Estimated adult survival was sex-dependent in the Scanian population, probably a result of differential neck band retention rates in this population. Mean juvenile survival was about 12% higher in the Scanian population (0.603 vs. 0.485). Adult survival in the Norwegian population was 0.728 (males 0.733; females 0.725), and in males and females from the Scanian population was 0.711 (0.752 after accounting for higher neck band loss in males) and 0.771, respectively. Over the course of the study, juvenile survival in the Scanian population increased substantially, and adult survival was constant, whereas both these parameters declined in the Norwegian population. This study demonstrates that the two Nordic populations are demographically distinct and gives further support to the notion that they should be treated as separate management units. The decline of 10% in adult survival in the Norwegian population, the cause of which still remains uncertain, is likely to have had a major impact on the growth of this population.     

Suggestive Structural Evidence for Macronuclear "Subnuclei" in Tetrahymena pyriformis GL

SYNOPSIS Structural changes in the Feulgen-positive material of the Tetrahymena pyriformis GL macronucleus have been observed during the cell cycle. From the finely granulated appearance in the interphase cell it appears as small rods, often arranged in pairs (probably the endomitotic stage) during early morphogenesis and as larger (and fewer) aggregates of granules during the nuclear division. These latter aggregates are also visible in dividing nuclei in the electron microscope where groups of chromation granules are separated by fairly empty nucleoplasm. It is suggested that these Feulgen positive aggregates in dividing nuclei are macronuciear segregation units or "subnuclei." The number per dividing macronucleus may vary from one experiment to another, but the variation seems to be related to cell volume. The distribution of the aggregates among the daughter nuclei is almost equal. The total number per dividing macronucleus is about 80 which is close to the estimated number of "subnuclei" in the T. pyriformis macronucleus (Allen and Nanney, 1958).
Some calculations are made on the polyploidy of the T. pyriformis GL macronucleus. Using published electron micrographs of micronuclei of known age to calculate the total number of chromatin granules per haploid nucleus, the polyploidy of the strain GL macronucleus is about 40. This figure is half of that expected from Allen and Nanney's estimation, since they assumed that the "subnuclei" were diploid; however, it is in agreement with the reported haploid nature of the "subnuclei" as found by Woodard, Gorovsky & Kaneshiro, 1968. Further calculations suggest that each macronuclear "chromosome" is composed of about 40 chromatin granules; an indication of such a chain arrangement of the chromatin granules has been observed in the phase contrast and electron microscope during the earliest macronuclear events, i.e., at the macronuclear "prophase."     

Characteristics of oligotrophic hardwater lakes in a postglacial land-rise area in mid-Sweden

1. We describe some remarkable ephemeral, oligotrophic hardwater lakes formed because of land rise in the coastal areas of the Baltic Sea, that are unique in Sweden and probably also worldwide. Two younger, coastal lakes were studied by regular sampling for 1 year and compared with an older (i.e. greater altitude) lake, that passed through the oligotrophic hardwater stage some 3–4000 years ago. 2. Despite some differences in composition of the catchment, the two younger lakes were similar with regard to water chemistry and plankton community composition. The concentration of phosphorus was low while nitrogen was high, resulting in very high N/P quotients (101 and 131). Although water colour was moderate, the concentration of organic carbon was extremely high (average values of ≥ 20 μg TOC L^–1), consisting mainly of dissolved compounds (DOC). 3. While the plankton was poorly developed, sediments in both lakes were covered by a layer of photosynthesising micro‐organisms. This substantial `microbial mat', which has not been described in detail before, was up to 15 cm thick and dominated by cyanobacteria and purple sulphur bacteria. The concentration of sediment phosphorus was extremely low (352 μg g^–1 dw) in one of the lakes and dominated by organic‐bound (residual) phosphorus. 4. Deep sediments in the older lake, representing its oligotrophic hardwater period, differed in phosphorus composition from the currently oligotrophic hardwater lakes by having a strong dominance of HCl‐extractable (Ca‐bound) phosphorus. This indicates that phosphorus, initially organic‐bound within the microbial mat, is subsequently bound to calcium. We hypothesise that this is promoted by the environmental conditions created by the benthic photosynthetic activity, in combination with the prevailing hardwater conditions. 5. The rich and flourishing microbial community on the sediments may also explain the high concentration of DOC in the lake.     

On the mechanism of floral shifts in speciation: gained pollination efficiency from tongue- to eye-attachment of pollinia in Platanthera (Orchidaceae)

This work explores the mechanism of floral shifts that may result in speciation. The model organisms chosen were the moth-pollinated pollinator-limited orchid species Platanthera bifolia and P. chlorantha . P. bifolia exhibits tongue-attachment of pollinia on pollinators, a character state that has been found previously to be ancestral. The close relative P. chlorantha exhibits the derived state of eye-attachment of pollinia on pollinators. We reasoned that differences between the species in pollination efficiency could give insights into the mechanism of floral shifts and thus cladogenesis. Four populations per species were investigated. In three populations, where the species were growing intermixed and were sharing pollinators, there was significant difference in the pollen export and import efficiency per visit-night (night with pollen export and/or import) between the two species. P. bifolia exported pollinia more efficiently but imported pollen less efficiently than did P. chlorantha . Pollen import was 1.7–4 times faster in P. chlorantha (eye-attachment) than it was in P. bifolia (tongue-attachment). P. chlorantha had a lower risk of interference between pollen import and export. An increase in fitness through greater speed and efficiency of pollen import due to an enlargement of the stigmatic surface and a reduction in the risk of sexual interference may therefore be mechanisms of the floral shift from tongue- to eye-attachment of pollinia on pollinators.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 481–495.     

The species delimitation problem applied to the Agabus bipustulatus complex (Coleoptera, Dytiscidae) in north Scandinavia

Agabus bipustulatus (Linnaeus) is one of the most common aquatic beetles in Europe. Two species have been traditionally recognized within the Palaearctic Agabus bipustulatus complex (Coleoptera, Dytiscidae) in Scandinavia: a lowland form A. bipustulatus and a high-altitude form A. solieri Aube. The specific status of solieri has been debated for more than a century but no quantitative investigation has been made to evaluate the status of this taxon. In this study we show that there is no clear-cut delimitation between the two forms, either morphological or genetic, across an altitudinal gradient in north Scandinavia. Morphological differences between 22 populations were analysed separately for each sex with both thin-plate splines relative warp analysis and 'classical-length' morphometries. Genetic variation at five polymorphic enzyme loci was analysed among seven populations. The morphological studies showed gradual variation correlated with altitude, in particular in the character that is traditionally used to separate solieri and bipustulatus , and in both the beetles' morphometric size and the lateral width of the metasternal plate, which is connected to flight capacity. The genetic study indicates that the a-Gpdh enzyme locus, which is involved in the transfer of energy to the flight muscles, is evidently subject to directional selection. Only minor population differences were observed without this system. Subdivision was found in some populations and was probably caused by migration from outside or within the local population. The overall conclusion is that there is no clear-cut species delimitation between A. bipustulatus and A. solieri in north Scandinavia. This indicates that A. solieri is a cold-adapted altitudinal form of the variable A. bipustulatus; additional support for this is the finding of solieri 'look alikes' in cold springs in areas normally inhabited by bipustulatus.