Productivity, herbivory, and species traits rather than diversity influence invasibility of experimental phytoplankton communities

Biological invasions are a major threat to natural biodiversity; hence, understanding the mechanisms underlying invasibility (i.e., the susceptibility of a community to invasions by new species) is crucial. Invasibility of a resident community may be affected by a complex but hitherto hardly understood interplay of (1) productivity of the habitat, (2) diversity, (3) herbivory, and (4) the characteristics of both invasive and resident species. Using experimental phytoplankton microcosms, we investigated the effect of nutrient supply and species diversity on the invasibility of resident communities for two functionally different invaders in the presence or absence of an herbivore. With increasing nutrient supply, increased herbivore abundance indicated enhanced phytoplankton biomass production, and the invasion success of both invaders showed a unimodal pattern. At low nutrient supply (i.e., low influence of herbivory), the invasibility depended mainly on the competitive abilities of the invaders, whereas at high nutrient supply, the susceptibility to herbivory dominated. This resulted in different optimum nutrient levels for invasion success of the two species due to their individual functional traits. To test the effect of diversity on invasibility, a species richness gradient was generated by random selection from a resident species pool at an intermediate nutrient level. Invasibility was not affected by species richness; instead, it was driven by the functional traits of the resident and/or invasive species mediated by herbivore density. Overall, herbivory was the driving factor for invasibility of phytoplankton communities, which implies that other factors affecting the intensity of herbivory (e.g., productivity or edibility of primary producers) indirectly influence invasions.     

Nitrogen isotopes in ectomycorrhizal sporocarps correspond to belowground exploration types

Nitrogen isotope values (δ¹⁵N) are higher in ectomycorrhizal fungi than in their plant hosts but the wide variability in δ¹⁵N among sporocarps of different fungal taxa is unexplained. We propose that fungal δ¹⁵N reflects sequestration of fungal nitrogen to build fungal biomass, and should accordingly reflect fungal exploration strategies and hyphal properties. To test this, we compared δ¹⁵N to exploration types, hyphal hydrophobicity, and the presence of rhizomorphs in ectomycorrhizal species from surveys at four sites in temperate and boreal coniferous forests. Fungi with exploration types of high biomass, such as long-distance (e.g., Suillus), medium-distance mat (e.g., Hydnellum), and medium-distance fringe (e.g., Cortinarius) were 4–7‰ more enriched in ¹⁵N than fungi with exploration types of low biomass [medium-distance smooth (e.g., Amanita), short-distance (e.g., Inocybe), and contact (e.g., Hygrophorus)]. High biomass types comprised 79% (Åheden, northern Sweden), 65% (Deer Park, Pacific Northwest, USA), 45% (Stadsskogen, central Sweden), and 39% (Hoh, Pacific Northwest, USA) of ectomycorrhizal species, with these types more prevalent at sites of lower nitrogen availability. Species with hydrophobic hyphae or with rhizomorphs were 3–4‰ more enriched in ¹⁵N than taxa with hydrophilic hyphae or without rhizomorphs. The consistency of these patterns suggest that δ¹⁵N measurements could provide insights into belowground functioning of poorly known taxa of ectomycorrhizal fungi and into relative fungal biomass across ectomycorrhizal communities.     

Bacterial diversity in faeces from polar bear (<Emphasis Type="Italic">Ursus maritimus</Emphasis>) in Arctic Svalbard

Background  

Polar bears (Ursus maritimus) are major predators in the Arctic marine ecosystem, feeding mainly on seals, and living closely associated with sea ice. Little is known of their gut microbial ecology and the main purpose of this study was to investigate the microbial diversity in faeces of polar bears in Svalbard, Norway (74-81°N, 10-33°E). In addition the level of bla _TEM alleles, encoding ampicillin resistance (amp^r) were determined. In total, ten samples were collected from ten individual bears, rectum swabs from five individuals in 2004 and faeces samples from five individuals in 2006.     

Mosaic structure of intragenic repetitive elements in histone H1-like protein Hc2 varies within serovars of <Emphasis Type="Italic">Chlamydia trachomatis</Emphasis>

Background  

The histone-like protein Hc2 binds DNA in Chlamydia trachomatis and is known to vary in size between 165 and 237 amino acids, which is caused by different numbers of lysine-rich pentamers. A more complex structure was seen in this study when sequences from 378 specimens covering the hctB gene, which encodes Hc2, were compared.     

Intestinal barrier function of Atlantic salmon (<Emphasis Type="Italic">Salmo salar</Emphasis> L.) post smolts is reduced by common sea cage environments and suggested as a possible physiological welfare indicator

Background  

Fish farmed under high intensity aquaculture conditions are subjected to unnatural environments that may cause stress. Therefore awareness of how to maintain good health and welfare of farmed fish is important. For Atlantic salmon held in sea cages, water flow, dissolved oxygen (DO) levels and temperature will fluctuate over time and the fish can at times be exposed to detrimentally low DO levels and high temperatures. This experimental study investigates primary and secondary stress responses of Atlantic salmon post smolts to long-term exposure to reduced and fluctuating DO levels and high water temperatures, mimicking situations in the sea cages. Plasma cortisol levels and cortisol release to the water were assessed as indicators of the primary stress response and intestinal barrier integrity and physiological functions as indicators of secondary responses to changes in environmental conditions.     

A placozoan affinity for Dickinsonia and the evolution of late Proterozoic metazoan feeding modes

SUMMARY Dickinsonia is one of the most recognizable forms in the Ediacaran fauna, but its phylogenetic position has been contentious, and it has been placed in almost every kingdom of life. Here, it is hypothesized that the affinities of Dickinsonia lie with the Placozoa (Metazoa), an understudied phylum that is widespread in tropical seas worldwide. Modern placozoans show obvious differences in size and axial organization compared with Dickinsonia, but these differences can be accounted for by the stem‐group/crown‐group distinction. The affinity with placozoans is evidenced primarily by the unique feeding mode of Dickinsonia, which is demonstrated by a series of feeding traces. These traces indicate that Dickinsonia moved over the Ediacaran matgrounds, and digested the mat using its entire lower sole. The ability of Dickinsonia to move negates an algal, fungal, or sponge affinity, while the feeding mode, external digestion with a ventral sole, rules out placement within any sponge or eumetazoan lineage. The only organisms that both move and feed in this manner are placozoans. Recent molecular phylogenetic studies have demonstrated that placozoans lie above sponges but below Eumetazoa. We hypothesize that Dickinsonia and other externally digesting Ediacaran forms are either stem‐placozoans, or a series of extinct lineages above sponges and below eumetazoans on the metazoan tree. We discuss the potential evolutionary transitions between the main metazoan feeding modes in the context of the emerging molecular phylogeny, and suggest that aspects of the sponge and placozoan feeding strategies are relicts of nonuniformitarian Proterozoic ocean conditions.     

Variation in the gut microbiota of laboratory mice is related to both genetic and environmental factors

During recent years, the composition of the gut microbiota (GM) has received increasing attention as a factor in the development of experimental inflammatory disease in animal models. Because increased variation in the GM might lead to increased variation in disease parameters, determining and reducing GM variation between laboratory animals may provide more consistent models. Both genetic and environmental aspects influence the composition of the GM and may vary between laboratory animal breeding centers and within an individual breeding center. This study investigated the variation in cecal microbiota in 8-wk-old NMRI and C57BL/6 mice by using denaturing gradient gel electrophoresis to profile PCR-derived amplicons from bacterial 16S rRNA genes. Comparison of the cecal microbiotas revealed that the similarity index of the inbred C57BL/6Sca strain was 10% higher than that of the outbred Sca:NMRI stock. Comparing C57BL/6 mice from 2 vendors revealed significant differences in the microbial profile, whereas the profiles of C57BL/6Sca mice raised in separate rooms within the same breeding center were not significantly different. Furthermore, housing in individually ventilated cages did not lead to intercage variation. These results show that denaturing gradient gel electrophoresis is a simple tool that can be used to characterize the gut microbiota of mice. Including such characterizations in future quality-control programs may increase the reproducibility of mouse studies.