Sulphide intrusion in eelgrass (Zostera marina L.)

Sudden events of seagrass die‐off have been suggested to be induced by invasion of the phytotoxin sulphide under environmental stress generating low oxygen supply in seagrass tissues. Laboratory experiments were conducted with eelgrass (Zostera marina L.) to measure intra‐plant changes in oxygen and sulphide by means of microelectrodes at different oxygen concentrations in the water column. The objectives were to examine whether sulphide intrusion into seagrass tissues can be induced, to determine the role of plant oxygen status for sulphide intrusion and to determine how fast internal sulphide pools are depleted after internal oxygen supplies have been restored. Under conditions with oxygen partial pressures (pO₂) above 7.4 kPa (> 35% of air saturation) within eelgrass rhizomes or meristematic tissues no intrusion of sulphide occurred in spite of high sediment concentrations of gaseous sulphide (> 1000 µm ). Lack of sulphide intrusion at high internal pO₂ suggested that oxygen release from the roots ensured complete re‐oxidation of sulphide in the rhizosphere. Under oxygen stress, however, the experiments clearly demonstrated intrusion of sulphide in eelgrass rhizomes and meristematic tissues. Rates of sulphide intrusion were controlled by internal pO₂, which in turn was controlled by water column oxygen concentrations. Maximum internal sulphide content reached 325 µm which by far exceeded the 1–10 µm known to inhibit mitochondrial activity in eukaryotic cells. Sulphide and low levels of oxygen could coexist in the eelgrass tissues reflecting fast internal transport of sulphide and slow rates of sulphide re‐oxidation. Upon re‐establishment of high internal oxygen concentrations the depletion of the sulphide pool was slow (half‐life = 20–30 min) indicating, that sulphide re‐oxidation within the eelgrass tissue was not bacterially or enzymatically facilitated but occurred by simple chemical oxidation. The results of this study are consistent with the proposed detrimental role of sulphide intrusion in events of sudden seagrass die‐off.     

DEVELOPMENT OF A PCR ASSAY SUITABLE FOR CAMPYLOBACTER SPP. MASS SCREENING PROGRAMS IN BROILER PRODUCTION

Campylobacter is the most common cause of human acute bacterial gastroenteritis worldwide. In order to comply with the demands of consumers for food free of bacterial pathogens, a mass screening program for Campylobacter in Danish broilers has been carried out based on conventional bacterial culture techniques since 1998. However, using conventional culture methods is time consuming and laborious, and therefore a Polymerase Chain Reaction (PCR) Campylobacter detection assay suitable for mass screening of cloacal swab samples from broilers was developed. By comparing the PCR detection with conventional culture methods, significantly more samples were found positive for Campylobacter with the PCR method. The PCR method is rapid, sensitive and suitable for mass screening for Campylobacter in poultry. Using this PCR method Campylobacter can be detected within 15 h. Notably, the method can be applied to detect Campylobacter directly from chicken feces at the species level.     

Browsed twig environmental DNA: diagnostic PCR to identify ungulate species

Ungulate browsing can have a strong effect on ecological processes by affecting plant community structure and composition, with cascading effects on nutrient cycling and animal communities. However, in the absence of direct observations of foraging, species‐specific foraging behaviours are difficult to quantify. We therefore know relatively little about foraging competition and species‐specific browsing patterns in systems with several browsers. However, during browsing, a small amount of saliva containing buccal cells is deposited at the bite site, providing a source of environmental DNA (eDNA) that can be used for species identification. Here, we describe extraction and PCR protocols for a browser species diagnostic kit. Species‐specific primers for mitochondrial DNA were optimized and validated using twigs browsed by captive animals. A time series showed that about 50% of the samples will amplify up to 12 weeks after the browsing event and that some samples amplify up to 24 weeks after browsing (12.5%). Applied to samples of natural browsing from an area where moose (Alces alces), roe deer (Capreolus capreolus), fallow deer (Cervus dama) and red deer (Cervus elaphus) are sympatric, amplification success reached 75%. This method promises to greatly improve our understanding of multispecies browsing systems without the need for direct observations.     

Respiration of midges (Diptera; Chironomidae) in British Columbian lakes: oxy-regulation, temperature and their role as palaeo-indicators

1. The specific respiration rate of 13 chironomid taxa and Chaoborus were measured to test the hypothesis of the relation between a species' ability to regulate their oxygen uptake and their distributional patterns among nine study lakes in British Columbia, Canada.
2. Respiration patterns of individual taxa were modelled using piecewise linear regression with break point and simple hyperbolic functions. Three types of respiration curves were identified: (i) classical oxy-conformers (e.g. littoral Cricotopus ) which cannot sustain a sufficient oxygen uptake with decreasing oxygen availability; (ii) oxy-regulators (e.g. profundal Chironomus ) which can regulate and maintain a constant respiration until a certain critical point and (iii) oxy-stressors ( Micropsectra ) which increase their respiration rate with decreasing oxygen availability until a critical point.
3. Respiration was measured at two different temperatures (10 and 20 °C), and over the range of oxygen saturation conditions studied here (0–90%) mean Q ₁₀ values varied from 1.3 to 2.5.
4. The results show that different chironomid taxa have varying sensitivity to low oxygen concentrations and different respiratory responses to increased temperature. The critical point increased to higher oxygen saturation for six taxa, decreased for one taxon and was unchanged for two taxa.
5. The results illustrate one of the possible biological mechanisms behind the use of chironomids as temperature and climate indicators in palaeoecological studies by exploring the link between temperature and respiration physiology.     

AN APPARATUS BASED ON TURBULENT MIXING FOR DELIVERY OF ODOROUS STIMULI

A simple olfactometer adaptable for animal and human experimentationis described. The apparatus is based on a principle of thoroughturbulent mixing and allows accurate determination of stimuluscomposition, concentration and duration. Several odours mightbe introduced simultaneously. The apparatus works both withgas and liquid. ^* Present address: Ekravn. 69, Oslo 7.     

Seasonal development and variation in abundance among four annual flight periods in a butterfly: a 20‐year study of the speckled wood (Pararge aegeria)

Insects typically spend the winter in a species‐specific diapause stage. The speckled wood butterfly, Pararge aegeria, is unique in having two alternative diapause stages, hibernating as larvae or pupae. In southern Sweden this creates a seasonal flight pattern with four annual adult flight periods: the first in May (pupal diapause), the second in June (larval diapause), and the third and fourth directly developing offspring generations in July and August, respectively. We address the raison d'être of the two diapause pathways by (1) outdoor rearing of cohorts, and (2) performing transect censuses throughout the season for 20 years. We contend that an early start of next season provides a benefit accruing to pupal diapause; conversely, a large proportion of the offspring from adults of the fourth flight peak are unable to reach the pupal stage before winter, providing a benefit accruing to larval winter diapause. The results obtained show that the two hibernation pathways are unlikely to be genetically distinct because of a strong overlap between the two offspring generations, and because sibling offspring from the third and fourth flight periods are likely to choose either of the two hibernation pathways, thereby resulting in a genetic mixing of the pathways. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 635–649.     

Diversity and distribution of subterranean bacteria in groundwater at Oklo in Gabon, Africa, as determined by 16S rRNA gene sequencing

This paper describes how groundwater was sampled, DNA extracted, amplified and cloned and how information available in the ribosomal 16S rRNA gene was used for mapping diversity and distribution of subterranean bacteria in groundwater at the Bangombé site in the Oklo region. The results showed that this site was inhabited by a diversified population of bacteria. Each borehole was dominated by species that did not dominate in any of the other boreholes; a result that probably reflects documented differences in the geochemical environment. Two of the sequences obtained were identified at genus level to represent Acinetobacter and Zoogloea , but most of the 44 sequences found were only distantly related to species in the DNA database. The deepest borehole, BAX01 (105 m), had the highest number of bacteria and also total organic carbon (TOC). This borehole harboured only Proteobacteria beta group sequences while sequences related to Proteobacteria beta, gamma and delta groups and Gram-positive bacteria were found in the other four boreholes. Two of the boreholes, BAX02 (34 m) and BAX04 (10 m) had many 16S rRNA gene sequences in common and they also had similar counts of bacteria, content of TOC, pH and equal conductivity, suggesting a hydraulic connection between them.