B. Boag

Competition and mutualism among the gut helminths of a mammalian host

Most animal species are infected with multiple parasite species; however, the role of interspecific parasite interactions in influencing parasite dynamics and shaping parasite communities has been unclear. Although laboratory studies have found evidence of cross-immunity, immunosuppression and competition, analyses of hosts in the field have generally concluded that parasite communities are little more than random assemblages. Here we present evidence of consistent interspecific interactions in a natural mammalian system, revealed through the analysis of parasite intensity data collected from a free-ranging rabbit (Oryctolagus cuniculus) population, sampled monthly for a period of 23 yr. The wild rabbit plays host to a diverse gut helminth community that reflects the communities seen in other economically important domestic herbivores. These findings suggest that parasite interactions could have profound implications for the dynamics of parasite communities. The efficacy of parasite control programmes could be jeopardized if such interactions are not taken into account. In contrast, a clear understanding of such interactions may provide the basis for the development of more environmentally acceptable methods of parasite control.

Spatial structure in soil chemical and microbiological properties in an upland grassland

We characterised the spatial structure of soil microbial communities in an unimproved grazed upland grassland in the Scottish Borders. A range of soil chemical parameters, cultivable microbes, protozoa, nematodes, phospholipid fatty acid (PLFA) profiles, community-level physiological profiles (CLPP), intra-radical arbuscular mycorrhizal community structure, and eubacterial, actinomycete, pseudomonad and ammonia-oxidiser 16S rRNA gene profiles, assessed by denaturing gradient gel electrophoresis (DGGE) were quantified. The botanical composition of the vegetation associated with each soil sample was also determined. Geostatistical analysis of the data revealed a gamut of spatial dependency with diverse semivariograms being apparent, ranging from pure nugget, linear and non-linear forms. Spatial autocorrelation generally accounted for 40-60% of the total variance of those properties where such autocorrelation was apparent, but accounted for 97% in the case of nitrate-N. Geostatistical ranges extending from approximately 0.6-6 m were detected, dispersed throughout both chemical and biological properties. CLPP data tended to be associated with ranges greater than 4.5 m. There was no relationship between physical distance in the field and genetic similarity based on DGGE profiles. However, analysis of samples taken as close as 1 cm apart within a subset of cores suggested some spatial dependency in community DNA-DGGE parameters below an 8 cm scale. Spatial correlation between the properties was generally weak, with some exceptions such as between microbial biomass C and total N and C. There was evidence for scale-dependence in the relationships between properties. PLFA and CLPP profiling showed some association with vegetation composition, but DGGE profiling did not. There was considerably stronger association between notional sheep urine patches, denoted by soil nutrient status, and many of the properties. These data demonstrate extreme spatial variation in community-level microbiological properties in upland grasslands, and that despite considerable numeric ranges in the majority of properties, overarching controlling factors were not apparent.

Climate disruption and parasite-host dynamics: patterns and processes associated with warming and the frequency of extreme climatic events

Levels of parasitism and the dynamics of helminth systems is subject to the impact of environmental conditions such that we may expect long term increases in temperature will increase the force of infection and the parasites basic reproduction number, R0. We postulate that an increase in the force of infection will only lead to an increase in mean intensity of adults when adult parasite mortality is not determined by acquired immunity. Preliminary examination of long term trends of parasites of rabbits and grouse confirm these predictions. Parasite development rate increases with temperature and while laboratory studies indicate this is linear some recent studies indicate that this may be non-linear and would have an important impact on R0. Warming would also reduce the selective pressure for the development of arrestment and this would increase R0 so that in systems like the grouse and Trichostrongylus tenuis this would increase the instability and lead to larger disease outbreaks. Extreme climatic events that act across populations appear important in synchronizing transmission and disease outbreaks, so it is speculated that climate disruption will lead to increased frequency and intensity of disease outbreaks in parasite populations not regulated by acquired immunity.

Feeding preferences of some earthworm species common to upland pastures in Scotland

Summary Six earthworm species common to upland Scottish pasture were offered soil and seven plant species of equal nutritional status common to pastures to determine if any dietary preferences existed. An analysis of variance showed that food types were removed differentially (p

Spatial variability of soil total C and N and their stable isotopes in an upland Scottish grassland

As preparation for a below ground food web study, the spatial variability of three soil properties (total N, total C and pH) and two stable isotopes (δ13C and δ15N of whole soil) were quantified using geostatistical approaches in upland pastures under contrasting management regimes (grazed, fertilised and ungrazed, unfertilised) in Scotland. This is the first such study of upland, north maritime grasslands. The resulting patterns of variability suggest that to obtain statistically independent samples in this system, a sampling distance of ≥13.5 m is required. Additionally, temporal change (a decline of 1‰) was observed in whole soil δ15N for the grazed, fertilised plot. This may have been caused by new inputs of symbiotically-fixed atmospheric N2.

Stable isotope natural abundances of soil, plants and soil invertebrates in an upland pasture

Abstract In an exploratory study of below-ground trophic relations, natural abundances of the stable isotope pairs 13C/12C and 15N/14N (δ13C and δ15N) were measured on samples of plant shoots, whole soil and soil invertebrates taken in 1994 from two contrasting treatments of a pre-existing experiment: (1) continued grazing by sheep, with N:P:K fertiliser additions from 1990 onward; and (2) no added fertiliser, but sheep grazing removed entirely. Stepwise trophic increases were documented better by seasonal averages of δ13C and δ15N and by seasonal trends, composed of data collected on several occasions, than by instantaneous values. Seasonal changes in plant monocot vs dicot differences for shoot δ13C and δ15N were detected from patterns over several individual sampling dates; instantaneous samples were neither statistically significant nor qualitatively interpretable. Significant isotopic differences between treatments were evident in invertebrates only as seasonal averages or trends. Seasonal variations of δ13C and δ15N in earthworms and slugs may reflect previously unsuspected invertebrate behaviour. Whole soil δ13C was static through time and across treatments. Whole soil δ15N changed seasonally, an effect consistent with 15N/14N fractionation, e.g. during denitrification.

Variation in host susceptibility and infectiousness generated by co-infection: the myxoma–Trichostrongylus retortaeformis case in wild rabbits

One of the conditions that can affect host susceptibility and parasite transmission is the occurrence of concomitant infections. Parasites interact directly or indirectly within an individual host and often these interactions are modulated by the host immune response. We used a free-living rabbit population co-infected with the nematode Trichostrongylus retortaeformis, which appears to stimulate an acquired immune response, and the immunosuppressive poxvirus myxoma. Modelling was used to examine how myxoma infection alters the immune-mediated establishment and death/expulsion of T. retortaeformis, and consequently affects parasite intensity and duration of the infection. Simulations were based on the general TH1–TH2 immunological paradigm that proposes the polarization of the host immune response towards one of the two subsets of T helper cells. Our findings suggest that myxoma infections contribute to alter host susceptibility to the nematode, as co-infected rabbits showed higher worm intensity compared with virus negative hosts. Results also suggest that myxoma disrupts the ability of the host to clear T. retortaeformis as worm intensities were consistently high and remained high in old rabbits. However, the co-infection model has to include some immune-mediated nematode regulation to be consistent with field data, indicating that the TH1–TH2 dichotomy is not complete. We conclude that seasonal myxoma outbreaks enhance host susceptibility to the nematode and generate highly infected hosts that remain infectious for a longer time. Finally, the virus–nematode co-infection increases heterogeneities among individuals and potentially has a large effect on parasite transmission.

Analysis of pollen in soils: processes of incorporation and redistribution of pollen in five soil profile types

Abstract In order to interpret soil pollen diagrams, knowledge on the processes of pollen incorporation and redistribution is essential. It has been suggested, with little direct supporting evidence, that pollen can move in soils through association with translocated organic matter, with soil water or as a result of soil faunal activity. We report the results of investigating pollen redistribution in a range of soil types through micromorphological analysis. It was possible to categorise, using fluorescent microscopy, the location of pollen grains within soil thin sections. The overall conclusion is the key role of soil fauna in causing the redistribution of pollen. It is only in accumulating organic horizons of peaty soils or podzols that pollen can be stratified and thus interpreted for palaeoenvironmental reconstruction.

Earthworm δ13C and δ15N analyses suggest that putative functional classifications of earthworms are site-specific and may also indicate habitat diversity

Abstract Natural abundances of the stable isotope pairs 13C/12C and 15N/14N ( δ 13 C and δ 15 N ) were measured from earthworms sampled from six sites with contrasting habitats (deciduous and coniferous woodland, arable and permanent pasture). Knowledge about the function of earthworms is important to the understanding of their ecology. The hypothesis, that endogeic (primarily soil and organic matter feeders) and epigeic (surface litter feeders, ingesting little or no soil) earthworms would be isotopically distinct and that isotopic values for anecic (surface litter and soil feeders) earthworms would fall between the other two groups based on their feeding strategies, was rejected. Earthworm δ 13 C and δ 15 N values from six sites indicated that classifying earthworms into the functional groups epigeic, anecic and endogeic is site-dependent. In contrast, δ values clearly separated earthworms into humic formers and humic feeders. Average 13C-enrichment (3.9‰) between earthworm and putative dietary source (vegetation) across all sites was larger than the typically reported enrichment (1‰) between a single trophic level suggesting that earthworms, as expected, derive nutrition from a number of sources, not just living vegetation. Enrichments of 13C and 15N in earthworms, relative to diet, could be developed as a tool for assessing habitat diversity.

Genetic variation in resistance to mixed, predominantly Teladorsagia circumcincta nematode infections of sheep: from heritabilities to gene identification

In cool temperate areas, such as Scotland, sheep are infected by a variety of nematodes but the dominant nematode is Teladorsagia circumcincta. Resistant animals have one or more of the following features: fewer adult nematodes, more inhibited larvae, shorter adult nematodes and decreased production of nematode eggs. In lambs at the end of the first grazing season, the heritability of adult worm length is very strong, whereas the heritability of egg production is moderate. The heritability of worm number is low while there is no detectable genetic variation in the number of inhibited larvae. The major mechanisms underlying resistance to T. circumcincta appear to be the IgA mediated suppression of worm growth and the mast cell mediated regulation of worm number. Mast cell responses are slow to develop, possibly because they are responsible for protein loss and reduced growth of the host. Two genes have been repeatedly associated with resistance to T. Circumcincta: the MHC class II DRB1 locus on chromosome 20 and the interferon‐γ locus on chromosome 3. Although the causative mutations are still unknown both genes are plausible candidates.