The catchment and climate regulation of pCO2 in boreal lakes

The regulation of surface water pCO₂ was studied in a set of 33 unproductive boreal lakes of different humic content, situated along a latitudinal gradient (57°N to 64°N) in Sweden. The lakes were sampled four times during one year, and analyzed on a wide variety of water chemistry parameters. With only one exception, all lakes were supersaturated with CO₂ with respect to the atmosphere at all sampling occasions. pCO₂ was closely related to the DOC concentration in lakes, which in turn was mainly regulated by catchment characteristics. This pattern was similar along the latitudinal gradient and at different seasons of the year, indicating that it is valid for a variety of climatic conditions within the boreal forest zone. We suggest that landscape characteristics determine the accumulation and subsequent supply of allochthonous organic matter from boreal catchments to lakes, which in turn results in boreal lakes becoming net sources of atmospheric CO₂.     

Dispersal and dormancy strategies among insect species competing for a pulsed resource

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Peribacteroid space acidification: a marker of mature bacteroid functioning in Medicago truncatula nodules

Legumes form a symbiotic interaction with Rhizobiaceae bacteria, which differentiate into nitrogen‐fixing bacteroids within nodules. Here, we investigated in vivo the pH of the peribacteroid space (PBS) surrounding the bacteroid and pH variation throughout symbiosis. In vivo confocal microscopy investigations, using acidotropic probes, demonstrated the acidic state of the PBS. In planta analysis of nodule senescence induced by distinct biological processes drastically increased PBS pH in the N₂‐fixing zone (zone III). Therefore, the PBS acidification observed in mature bacteroids can be considered as a marker of bacteroid N₂ fixation. Using a pH‐sensitive ratiometric probe, PBS pH was measured in vivo during the whole symbiotic process. We showed a progressive acidification of the PBS from the bacteroid release up to the onset of N₂ fixation. Genetic and pharmacological approaches were conducted and led to disruption of the PBS acidification. Altogether, our findings shed light on the role of PBS pH of mature bacteroids in nodule functioning, providing new tools to monitor in vivo bacteroid physiology.     

Cold‐induced expression of diapause in Praon volucre: fitness cost and morpho‐physiological characterization

Cold exposure (2°C for 7 days) in constant darkness at mummy stage induces diapause expression in 9% of the Praon volucre Haliday population. Diapausing parasitoids show a significant delay in emergence time compared with nondiapausing counterparts. A diapause‐mediated polyphenism is observed in mummy colour, with diapausing mummies being clearly darker than nondiapausing ones. The diapause status of dark mummies is confirmed by a significant reduction in metabolic rate. Diapausing parasitoids also display specific morphological characteristics: they are heavier (fresh and dry mass) and accumulate larger fat reserves than nondiapausing counterparts. The diapause status is associated with a fitness cost in terms of adult longevity. There is no evidence of diapause‐related change in supercooling ability.     

Micro‐ and nano‐scale ultrastructure of cell walls in Cryogenian microfossils: revealing their biological affinity

Moczyd?owska, M., Schopf, J.W. & Willman, S. 2009: Micro‐ and nano‐scale ultrastructure of cell walls in Cryogenian microfossils: revealing their biological affinity. Lethaia, Vol. 43, pp. 129–136. Recently established protocols and methods in advanced microscopy and spectrometry applied to studies of ancient unicellular organic‐walled microfossils of uncertain biological affinities (acritarchs) provide new evidence of the fine ultrastructure of cell walls and their biochemistry that support the interpretation of some such microfossils as photosynthesizing microalgae. The micro‐scale and nanoscale ultrastructure of the cell walls of late Cryogenian sphaeromorphic acritarchs from the Chichkan Formation (Kazakhstan) revealed by the advanced techniques and studied originally by Kempe et al. (2005) is here further analysed and compared with that of modern microalgal analogues. On the basis of such comparison, we interpret the preserved cell wall ultrastructure to reflect original layering and lamination within sub‐layers of the fossil wall, rather than being a result of taphonomic and diagenetic alteration. The outer thick layer represents the primary wall and the inner layer the secondary wall of the cell, whereas the laminated amorphous sub‐layers, 10–20 nm in thickness and revealed by transmission electron and atomic force microscopy, are recognized as trilaminar sheath structure. Because two‐layered cell walls, trilaminar sheaths and the position of the TLS within the fossil cell wall are characteristic of the mature developmental state in cyst morphogenesis in modern microalgae, we infer that the Chichkan sphaeromorphs are probably resting cells (aplanospores) of chlorophyceaen green microalgae from the order Volvocales. □Biological affinity, cell wall, Cryogenian, microfossils, ultrastructure.     

One hundred years of instability in ensiferan relationships

Although Ensifera is a major insect model group, its phylogenetic relationships have been understudied so far. Few phylogenetic hypotheses have been proposed, either with morphological or molecular data. The largest dataset ever used for phylogeny reconstruction on this group is molecular (16S rRNA, 18S rRNA and 28S rRNA sequences for 51 ensiferan species), which has been used twice with different resultant topologies. However, only one of these hypotheses has been adopted commonly as a reference classification. Here we re‐analyse this molecular dataset with different methods and parameters to test the robustness and the stability of the adopted phylogeny. Our study reveals the instability of phylogenetic relationships derived from this dataset, especially for the deepest nodes of the group, and suggests some guidelines for future studies. The comparison between the different classifications proposed in the past 70 years for Ensifera and our results allows the identification of potential monophyletic clades (katydids, mole crickets, scaly crickets + Malgasia, true crickets, leaf roller crickets, cave crickets) and the remaining unresolved clades (wetas, Jerusalem crickets and most of the highest rank clades) in Ensifera phylogeny.     

Infestation of commercial bumblebee (Bombus impatiens) field colonies by small hive beetles (Aethina tumida)

Abstract.  1. The small hive beetle, Aethina tumida , is a parasite of honeybee ( Apis mellifera ) colonies native to sub-Saharan Africa and has become an invasive species. In North America the beetle is now sympatric with bumblebees, Bombus , not occurring in its native range. Laboratory studies have shown that small hive beetles can reproduce in bumblebee colonies but it was not known whether infestations occur in the field.
2. For the first time, infestation of bumblebee colonies by small hive beetles was investigated in the field. Commercial Bombus impatiens colonies ( n = 10) were installed in proximity to infested apiaries. Within 8 weeks, all colonies that were alive in the 5-week observation period ( n = 9) became naturally infested with adult small hive beetles and successful small hive beetle reproduction occurred in five colonies.
3. In four-square choice tests, the beetles were attracted to both adult bumblebee workers and pollen from bumblebee nests, suggesting that these odours may serve as cues for host finding.
4. The data indicate that bumblebee colonies may serve as alternative hosts for small hive beetles in the field. To foster the conservation of these essential native pollinators, investigations on the actual impact of small hive beetles on wild bumblebee populations are suggested.     

Harmonising the bioassessment of large rivers in the absence of near‐natural reference conditions – a case study of the Danube River

1. International river catchments pose challenges for effective water resource management. Catchment‐wide strategies are often complicated by differences in national bioassessment and quality classification. Intercalibration efforts aim to harmonise these differences, but rely on the consistent delineation of near‐natural reference sites that are almost unavailable in today’s landscape, especially for large rivers. 2. We introduce the concept of alternative benchmarking that is based on the notion of aquatic communities at similar (low) levels of impairment associated with least‐disturbed conditions (LDC) as defined by abiotic criteria. Using data acquired during the second Joint Danube Survey, we defined LDC sites based on a multivariate gradient of anthropogenic pressures, mostly related to morphological deterioration, that spans the entire navigable Danube. 3. The river was subdivided into four stretches, each featuring homogeneous biological assemblages. Indirect gradient analysis revealed relationships between the pressure gradient and selected features of the macroinvertebrate and macrophyte community but not for diatoms or phytoplankton. 4. We identified biological metrics suitable for the quality classification of individual stretches or the entire river. Impoundment is the major hydromorphological alteration on the Danube but various metrics still responded significantly to differences in the morphological condition of sites not affected by impoundment. 5. A comparison of macroinvertebrate sampling techniques (airlift versus kick‐and‐sweep) revealed differences in how the acquired data reflect the effects of anthropogenic pressure. Biological metrics based only on kick‐and‐sweep sample data were insensitive to habitat deterioration in the heavily modified Upper Danube. 6. This study exemplifies the empirical approach of alternative benchmarking in intercalibration and offers practical solutions to some of the challenges of large river bioassessment.