Contrasting seasonal niche separation between rare and abundant taxa conceals the extent of protist diversity

With the advent of molecular methods, it became clear that microbial biodiversity had been vastly underestimated. Since then, species abundance patterns were determined for several environments, but temporal changes in species composition were not studied to the same level of resolution. Using massively parallel sequencing on the 454 GS FLX platform we identified a highly dynamic turnover of the seasonal abundance of protists in the Austrian lake Fuschlsee. We show that seasonal abundance patterns of protists closely match their biogeographic distribution. The stable predominance of few highly abundant taxa, which previously led to the suggestion of a low global protist species richness, is contrasted by a highly dynamic turnover of rare species. We suggest that differential seasonality of rare and abundant protist taxa explains the—so far—conflicting evidence in the ‘everything is everywhere’ dispute. Consequently temporal sampling is basic for adequate diversity and species richness estimates.     

Peptide-Induced Morphogenesis in the Nematode-Trapping Fungus Arthrobotrys oligospora

The present investigation shows the ability of peptides to induce capture organ formation in Arthrobotrys oligospora when applied in a synthetic low nutrient medium. Under certain conditions casitone was shown to induce capture organ formation. The active principle in casitone was concentrated and purified by alternating procedures of ion exchange chromatography and gel chromatography in pyridine-acetic acid buffers. Crude casitone solutions were applied to columns of Dowex 50 W-X2 and eluted stepwise with 0.1–1.0 M pyridine-acetic acid pH 3.2–5.1. Active portions, free from most acid and neutral amino acids, were further purified on columns of Sephadex G-10 in 0.1 M pyridine-acetic acid pH 4.6. Aromatic amino acids and large molecules in the void volume could be separated from an active peptide mixture which was subjected to renewed ion exchange chromatography on Bio-Rad AG 50 W-X2. By stepwise and/or gradient elution in 0.1–0.5 M pyridine-acetic acid pH 3.2 fairly purified peptides were obtained. The composition of the test medium is an important factor in spontaneous capture organ formation. The peptides isolated from casitone induced capture organ formation, when given to the fungus in a synthetic mineral salt medium supplied with thiamin and biotin. Similar effects were obtained with small synthetic peptides in the same concentration (0.1 mg/ml). A large variety of peptides seem to be active when applied in a suitable medium. This was especially true for peptides with Rf > Rf_leu on thin layers of cellulose developed with butanol-acetic acid-water (4: 1: 1). Of the peptides investigated valyl-peptides exerted the most drastic effect.     

Immediate and long-term nitrogen oxide emissions from tropical forest soils exposed to elevated nitrogen input

Tropical nitrogen (N) deposition is projected to increase substantially within the coming decades. Increases in soil emissions of the climate‐relevant trace gases NO and N₂O are expected, but few studies address this possibility. We used N addition experiments to achieve N‐enriched conditions in contrasting montane and lowland forests and assessed changes in the timing and magnitude of soil N‐oxide emissions. We evaluated transitory effects, which occurred immediately after N addition, and long‐term effects measured at least 6 weeks after N addition. In the montane forest where stem growth was N limited, the first‐time N additions caused rapid increases in soil N‐oxide emissions. During the first 2 years of N addition, annual N‐oxide emissions were five times (transitory effect) and two times (long‐term effect) larger than controls. This contradicts the current assumption that N‐limited tropical montane forests will respond to N additions with only small and delayed increases in soil N‐oxide emissions. We attribute this fast and large response of soil N‐oxide emissions to the presence of an organic layer (a characteristic feature of this forest type) in which nitrification increased substantially following N addition. In the lowland forest where stem growth was neither N nor phosphorus (P) limited, the first‐time N additions caused only gradual and minimal increases in soil N‐oxide emissions. These first N additions were completed at the beginning of the wet season, and low soil water content may have limited nitrification. In contrast, the 9‐ and 10‐year N‐addition plots displayed instantaneous and large soil N‐oxide emissions. Annual N‐oxide emissions under chronic N addition were seven times (transitory effect) and four times (long‐term effect) larger than controls. Seasonal changes in soil water content also caused seasonal changes in soil N‐oxide emissions from the 9‐ and 10‐year N‐addition plots. This suggests that climate change scenarios, where rainfall quantity and seasonality change, will alter the relative importance of soil NO and N₂O emissions from tropical forests exposed to elevated N deposition.     

Impact of hydrology on free-living and particle-associated microorganisms in a river floodplain system (Danube, Austria)

1. A floodplain segment of the Danube River downstream of Vienna was studied during the hydrologically most dynamic phase (spring–summer) to evaluate the significance of connection between the main channel and the floodplain segment for particle abundance and quality as well as for bacterial and viral parameters, both free‐living and attached to particles. 2. Hydrological connectivity between the main channel and its floodplain segment (expressed as water age) influenced particle abundance and quality. Polysaccharide‐containing particles [Alcian positive‐stained particles (ASP)] and protein‐containing particles [Coomassie positive‐stained particles (CSP)] each contributed a substantial fraction to total suspended solids and were both positively related to water age. ASP were about twice as abundant as CSP. 3. Water age influenced bacterial and viral abundance and the bacterioplankton productivity in the surrounding water. Free‐living bacterial abundance and their bacterial secondary production (BSP) increased continuously with water age, best described by a linear regression. Water age also significantly impacted BSP and per cell BSP of bacteria attached to particles. The abundance of attached bacteria and viruses was not influenced by water age. 4. Bacteria and viruses on particles were influenced by particle quality. Their abundance on particles was closely related to particle size. Particle‐attached bacteria accounted on average for 30.34% (± 3.09) of the total bacterial abundance. A variable and occasionally significant proportion of viruses, between 0.43% and 35.06%, were associated with particulate material. 5. Bacteria attached to particles were significantly more productive than their free‐living counterparts. Their per‐cell activity was on average 8.6 times higher than that of the free‐living fraction. 6. Hydrological connectivity between the Danube River and its floodplain is crucial not only for the exchange of water, sediment and nutrients, but also for microbiota, thus influencing microbial life, distribution and activity.     

Impact of a social parasite on ant host populations depends on host species,habitat and year

Parasites often affect the abundance and life‐history traits of their hosts. We studied the impact of a social parasite – a slavemaking ant – on host ant communities using two complementary field manipulations. In the first experiment, we analysed the effect of social parasite presence on host populations in one habitat. In a second experiment, conducted in two habitats, we used a cross‐fostering design, analysing the effect of sympatric and allopatric social parasites. In the first experiment, host colonies benefited to some extent from residing in parasite‐free areas, showing increased total production. Yet, in the second experiment, host colonies in plots containing social parasites were more productive, and this effect was most evident in response to allopatric social parasites. We propose several explanations for these inconsistent results, which are related to environmental variability. The discrepancies between the two habitats can be explained well by ecological variation as a result of differences in altitudes and climate. For example, ant colonies in the colder habitat were larger and, for one host species, colonies were more often polygynous. In addition, our long‐term documentation – a total of four measurements of community structure in 6 years – showed temporal variation in abundance and life‐history traits of ant colonies, unrelated to the manipulations. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 559–570.     

Bacterial metabolism in the River Danube: parameters influencing bacterial production

1. Microbial parameters were determined at five sampling sites in the River Danube up-and downstream of Vienna, Austria, twice monthly over an annual cycle. Bacterial production (BP) was estimated from thymidine and leucine incorporations; additionally, the effect of turbulence on BP and the conversion factors for converting incorporation rates into bacterial cell production were determined using the cumulative approach. 2. BP under turbulent conditions was not significantly different from that under stagnant conditions. For thymidine, a mean annual conversion factor of 3.2 ± 10¹⁸ cells mol^?1 thymidine incorporated was calculated. For leucine, the corresponding factor was 0.07 ± 10¹⁸ cells mol^?1 leucine. Average annual BP calculated by thymidine incorporation was significantly higher than BP calculated from leucine incorporation and ranged from 47.2 to 77.5 μg C 1-^?1 day^?1 depending on the tracer and the conversion factor used. 3. Bacterial growth rates ranged from 0.1 day^?1 during winter to 1.7 day^?1 in the summer. A strong correlation was found between temperature as well as chlorophyll a and bacterial growth when temperature was greater than 5 °C; a major spring phytoplankton bloom at a temperature below 5 °C did not increase BP. 4. Dissolved organic carbon (DOC) concentrations varied between 2 and 7.2 mg C 1-^?1 and comprised between 50 and 92% of the total organic carbon pool in the River Danube, Based on the DOC concentration and an assumed bacterial growth yield of 20% we calculated mean DOC turnover times of around 60 days in the winter and less than 8 days during the summer.     

Qualitative Characterization of Some Peptides Inducing Morphogenesis in the Nematode- Trapping Fungus Arthrobotrys oligospora

Some peptides inducing capture organ formation in Arthrobotrys oligospora were characterized with regard to their amino acid contents. The N-terminal, C-terminal and total amino acids were determined as their dinitrophenyl-derivatives by thin layer chromatography on silica gel in two different solvents. The amino acid composition was further confirmed by gas-liquid chromatography. The peptides investigated had a high proportion of non-polar and aromatic residues. Thus, leucine, isoleucine, valine, proline, and tyrosine were present in all the peptides. In addition, phenyl-alanine, glycine, and alanine occurred in some preparations. Tyrosine, valine, and phenylalanine were found in N-terminal position, and leucine or isoleucine were C-terminals.     

High microbial activity on glaciers: importance to the global carbon cycle

Cryoconite holes, which can cover 0.1–10% of the surface area of glaciers, are small, water-filled depressions (typically <1 m in diameter and usually <0.5 m deep) that form on the surface of glaciers when solar-heated inorganic and organic debris melts into the ice. Recent studies show that cryoconites are colonized by a diverse range of microorganisms, including viruses, bacteria and algae. Whether microbial communities on the surface of glaciers are actively influencing biogeochemical cycles or are just present in a dormant state has been a matter of debate for long time. Here, we report primary production and community respiration of cryoconite holes upon glaciers in Svalbard, Greenland and the European Alps. Microbial activity in cryoconite holes is high despite maximum temperatures seldom exceeding 0.1 °C. In situ primary production and respiration in cryoconites during the summer is often comparable with that found in soils in warmer and nutrient richer regions. Considering only glacier areas outside Antarctica and a conservative average cryoconite distribution on glacial surfaces, we found that on a global basis cryoconite holes have the potential to fix as much as 64 Gg of carbon per year (i.e. 98 Gg of photosynthesis minus 34 Gg of community respiration). Most lakes and rivers are generally considered as heterotrophic systems, but our results suggest that glaciers, which contain 75% of the freshwater of the planet, are largely autotrophic systems.     

Effects of the introduced ectoparasite Philornis downsi on haemoglobin level and nestling survival in Darwin's Small Ground Finch (Geospiza fuliginosa)

Abstract: The physiological impacts and fitness costs of parasitism by an introduced ectoparasitic fly, Philornis downsi (Muscidae), were studied in nestlings of Darwin's Small Ground Finch, Geospiza fuliginosa (Geospizinae), on the Galápagos Archipelago. Whole blood haemoglobin (Hb) concentration was used to measure host response to ectoparasitism due to its high repeatability and validity, as well as for its key role in aerobic activities that affect fitness, such as flight capacity and nestling begging intensity. Increased numbers of ectoparasitic larvae of P. downsi were strongly correlated with lower Hb levels in nestlings in the absence of blood parasites. Furthermore, immature red blood cell counts were negatively correlated with Hb level and positively correlated with P. downsi intensity. Nestlings with high levels of parasitism suffered higher mortality, which varied with clutch size. Our results provide evidence that endemic Galápagos bird populations are physiologically compromised by P. downsi and experience substantial fitness costs due to ectoparasitism.