Benzimidazole resistance of sheep nematodes in Norway confirmed through controlled efficacy test

ABSTRACT: BACKGROUND: Resistance against benzimidazoles (BZ) has recently been detected in Norwegian sheep flocks through a large scale prevalence survey based on the faecal egg count reduction test (FECRT). The use of this test in combination with bulk larval culture only gives an indication of which gastrointestinal nematodes genera that are involved and these results have to be confirmed by a controlled efficacy test (CET) to get accurate information about resistant nematodes populations at species level. A CET was therefore performed with larvae from two flocks where BZ resistance was previously detected through FECRT. RESULTS: The latter test confirmed the previous results in both flocks. In flock A, the BZ resistant nematode population consisted solely of Haemonchus contortus, whereas H. contortus and Teladorsagia circumcincta comprised the resistant worm population in flock B. CONCLUSIONS: Some discrepancies that have been recorded between FECRT and CET results regarding time for post-treatment coproscopical examination and a temporary suppression of faecal egg excretion are discussed.     

Large scale experimental effects of three levels of sheep densities on an alpine ecosystem

Plant–herbivore dynamics is a major topic in ecological research, but empirical knowledge on the ecological effects of different densities of large grazers from fully replicated experiments is rare. Previous studies have focused on grazing vs no grazing, and our understanding of the extent to which different levels of grazing alter vegetation composition, and how quickly such effects can be measured, is therefore limited. We performed a fully replicated, short‐term (four‐year) experiment using large enclosures (each ～0.3 km²) with three different sheep densities (no grazing, low grazing and high grazing, respectively) in an alpine environment with summer grazing in southern Norway to address these issues. Sheep grazing mainly affected plant species at high densities of sheep as compared to no sheep after a four‐year treatment; few effects of low sheep densities were detectable. Highly selected herbs, herbs suggested vulnerable to trampling, and woody species decreased, while most graminoids, one ruderal, one prostrate species and two bryophyte taxa increased at high sheep densities. We found contrasting responses within main functional groups highlighting that fine details of plant life histories need to be known for responses to grazing to be successfully predicted. Vascular plant cover and bare soil responded to sheep density after two years of treatment, but only for one of the species was frequency change observed at this stage. Overall, plants in low grazing plots were found to be almost unaffected. Changes in abundance were mainly found at the no grazing and high grazing treatments. Plant species that decreased at high grazing generally increased at no grazing and vice versa, suggesting a response to both cessation of grazing and enhanced grazing respectively. Our study demonstrates, beyond a simple comparison of heavily grazed and non‐grazed sites, that herbivore effects on plants are typically non‐linearly related to herbivore density, and that the speed of plant responses will depend both on the plant property examined and the grazing pressure.     

Timing and abundance as key mechanisms affecting trophic interactions in variable environments

Climatic changes are disrupting otherwise tight trophic interactions between predator and prey. Most of the earlier studies have primarily focused on the temporal dimension of the relationship in the framework of the match–mismatch hypothesis. This hypothesis predicts that predator's recruitment will be high if the peak of the prey availability temporally matches the most energy‐demanding period of the predators breeding phenology. However, the match–mismatch hypothesis ignores the level of food abundance while this can compensate small mismatches. Using a novel time‐series model explicitly quantifying both the timing and the abundance component for trophic relationships, we here show that timing and abundance of food affect recruitment differently in a marine (cod/zooplankton), a marine–terrestrial (puffin/herring) and a terrestrial (sheep/vegetation) ecosystem. The quantification of the combined effect of abundance and timing of prey on predator dynamics enables us to come closer to the mechanisms by which environment variability may affect ecological systems.     

Negative density-dependent emigration of males in an increasing red deer population

In species with polygynous mating systems, females are regarded as food-limited, while males are limited by access to mates. When local density increases, forage availability declines, while mate access for males may increase due to an increasingly female-biased sex ratio. Density dependence in emigration rates may consequently differ between sexes. Here, we investigate emigration using mark-recovery data from 468 young red deer Cervus elaphus marked in Snillfjord, Norway over a 20-year period when the population size has increased sixfold. We demonstrate a strong negative density-dependent emigration rate in males, while female emigration rates were lower and independent of density. Emigrating males leaving the natal range settled in areas with lower density than expected by chance. Dispersing males moved 42 per cent longer at high density in 1997 (37 km) than at low density in 1977 (26 km), possibly caused by increasing saturation of deer in areas surrounding the marking sites. Our study highlights that pattern of density dependence in dispersal rates may differ markedly between sexes in highly polygynous species. Contrasting patterns reported in small-scale studies are suggestive that spatial scale of density variation may affect the pattern of temporal density dependence in emigration rates and distances.     

Greenhouse Gas Emissions from Freshwater Reservoirs: What Does the Atmosphere See?

Freshwater reservoirs are a known source of greenhouse gas (GHG) to the atmosphere, but their quantitative significance is still only loosely constrained. Although part of this uncertainty can be attributed to the difficulties in measuring highly variable fluxes, it is also the result of a lack of a clear accounting methodology, particularly about what constitutes new emissions and potential new sinks. In this paper, we review the main processes involved in the generation of GHG in reservoir systems and propose a simple approach to quantify the reservoir GHG footprint in terms of the net changes in GHG fluxes to the atmosphere induced by damming, that is, ‘what the atmosphere sees.’ The approach takes into account the pre-impoundment GHG balance of the landscape, the temporal evolution of reservoir GHG emission profile as well as the natural emissions that are displaced to or away from the reservoir site resulting from hydrological and other changes. It also clarifies the portion of the reservoir carbon burial that can potentially be considered an offset to GHG emissions.     

Identification of plant volatiles activating single receptor neurons in the pine weevil (Hylobius abietis)

Naturally produced plant volatiles, eliciting responses of single olfactory receptor neurons in the pine weevil, have been identified by gas chromatography linked with mass spectrometry. The receptor neurons (n = 72) were classified in 30 types, according to the compound which elicited the strongest response in each neuron, 20 of which compounds were identified. Most potent for 14 types of neurons (n = 50) were monoterpenes, including bicyclic (e.g. α-pinene, camphor and myrtenal) for 8 types (n = 32), monocyclic (limonene, carvone, α-terpinene) for 3 types (n = 12) and acyclic (e.g. β-myrcene and linalool) for 3 types (n = 6). Other compounds eliciting strongest responses of a neuron were five sesquiterpenes, including α-copaene and a farnesene-isomer, and an anethole type which has no biosynthetic relationship with terpenes. Within one type, receptor neurons with quite selective responses to the most potent compound as well as neurons with additional responses to several, structurally similar compounds were found, indicating that the neurons may have the same functional types of membrane receptors, but different sensitivities. Response spectra of neurons within the bicyclic-, mono-cyclic and acyclic types showed more overlapping than across the neuron types. Minimal overlapping response spectra was found between monoterpene and sesquiterpene neurons. The results suggest that this structure-activity relationship is significant for encoding plant odour information in the pipe weevil. Accepted: 6 January 1997     

Cloning and characterization of rac-like cDNAs from Arabidopsis thaliana

The Rho family of GTPases are in higher eukaryotes divided into 3 major subfamilies; the Rho, Rac and Cdc42 proteins. In plants, however, the Rho family is restricted to one large family of Rac-like proteins. From work with mammalian phagocytes the Rac proteins are known to activate a multicomponent NADPH-dependent oxidase which results in accumulation of H₂O₂, a process termed oxidative burst. In plants a similar oxidative burst is observed and plays an important role in its defence against pathogen infections, suggesting a similar role for the plant Rac-like proteins. The Rho family of GTPases proteins are also involved in control of cell morphology, and are also thought to mediate signals from cell membrane receptors.In a broad search for members of the Ras superfamily in plants, several new small GTP-binding proteins were found. We report here the identification and molecular cloning of 5 rac-like cDNAs from Arabidopsis thaliana, Arac1–5. The Rac-like proteins deduced from the cDNA sequences all share 80–95% homology, but show considerably more diversity on the nucleotide level, indicating that this is an ancient gene family. Four of the rac genes were found to be expressed in all tissues examined, but one gene, Arac2, was expressed exclusively in the root, hypocotyl and stem. Our results show that the rac gene family in A. thaliana consists of at least 10 different genes.     

Early onset of reproductive senescence in domestic sheep Ovis aries

A central theme in life history theory is to determine how reproduction varies with age in iteroparous organisms. Evidence of ageing and senescence, defined as the progressive loss of function accompanied by decreased performance with age, remains poorly documented for large herbivores, in particular as it relates to reproduction. Analyses of body weight of 87 532 domestic sheep lambs demonstrates that onset of reproductive senescence in ewes occurs already at 5 and 6 years of age when measured, respectively, as lamb weight and litter size produced. This provides convincing evidence of early onset of reproductive senescence in this highly domesticated sheep breed. As this is earlier than indicated for other Ovis species as well as for the Soay sheep, an ancient and lightly domesticated sheep, we hypothesize that there may be a cost of selection for large litter size in mammalian herbivores.     

Sexual size dimorphism and reproductive ecology in relation to mating system in waders

The relationship between sexual size dimorphism, body-weight and different reproductive traits (e.g. clutch size, egg weight and incubation period) in relation to mating system and forms of parental care was studied in waders. Two hypotheses were examined. (1) Sexual size dimorphism is correlated with the intensity of sexual selection. (2) The degree of sexual size dimorphism is the result of an interrelationship between the reproductive strategy of the female and her body size. In the polygynous species the male was significantly larger than the female. This is consistent with the sexual selection hypothesis. However, among waders, a positive correlation exists between egg weight, clutch mass and body-weight. Selection for small eggs or a short incubation period may therefore have an influence on female body-weight. If the lack of paternal care reduces the female's possibility for producing large eggs or incubating a large clutch mass, we would expect a selection pressure for small female size among polygynous species. Thus, large sexual size dimorphism among polygynous waders may be a result of selection for small female size to lack of paternal care, or selection for large male size due to intramale competition or a female preference for large-sized males. In multiple-clutch species (viz. species in which the female regularly lays more than one clutch during the season) egg weight was low both for a given female and male body-weight. The low egg weight of multiple-clutch species is assumed to be a result of the constraints placed on the female from producing several clutches during a single breeding season.