Search

Within-host models of infection can provide important insights into the processes that affect parasite spread and persistence in host populations. However, modeling is often limited by the availability of empirical data, a problem commonly encountered in natural systems. Here, we used six years of immune-infection observations of two gastrointestinal helminths (Trichostrongylus retortaeformisandGraphidium strigosum) from a population of European rabbits (Oryctolagus cuniculus) to develop an age-dependent, within-host mathematical model that explicitly included species-specific and cross-reacting antibody (IgA and IgG) responses to each helminth in hosts with single or dual infections. Different models of single infection were formally compared to test alternative mechanisms of parasite regulation. The two models that best described single infections of each helminth species were then coupled through antibody cross-immunity to examine how the presence of one species could alter the host immune response to, and the within-host dynamics of, the other species. For both single infections, model selection suggested that either IgA or IgG responses could equally explain the observed parasite intensities at different host age. However, the strength of this response drastically changed between the two helminths, being stronger againstT. retortaeformisthan againstG. strigosumand causing contrasting age-intensity profiles. When the two helminths coinfect the same host, we found a decrease of the species-specific immune response to both species together with an asymmetric cross-immune response driven by IgG. Changes in the level and affinity of antibodies from single to dual infections contributed to the significant increase of both helminth abundances. By combining mathematical modeling with immuno-infection data, our work provides a model framework for disentangling some of the complexities generated by host-parasite and parasite-parasite interactions from natural systems. Our approach thus offers a tractable general tool to examine immune-infection relationships within hosts.Author summaryThe host immune response often plays a critical role in regulating parasite dynamics and transmission. We developed a mathematical model to evaluate whether and how the observed variation in host antibody responses could explain the relative differences in the abundance of two parasite species in hosts with single and dual infections from a natural rabbit population. Our results indicated that either IgA or IgG could describe the contrasting trends of the two parasites in rabbits with single infections. Specifically, antibodies appeared to controlT. retortaeformis, while the effect was less clear forG. strigosum. For dual infections, we found a weaker specific antibody response against both helminths and an asymmetric cross-immunity, which could explain the significantly greater intensities observed forT. retortaeformisand, secondly, forG. strigosum. Our within-host mathematical framework provides a plausible mechanism for the mediated role of antibodies in hosts with single and dual parasite infections, and how the strength of these infection-immune interactions changes with host age. This model framework offers a way forward to our understanding of the within-host processes that generate individual variation in infection and is relatively flexible to be applied to other natural systems.

The conceptual understanding of immune-mediated interactions between parasites is rooted in the theory of community ecology. One of the limitations of this approach is that most of the theory and empirical evidence has focused on resource or immune-mediated competition between parasites and yet there is ample evidence of positive interactions that could be generated by immune-mediated facilitation. We developed an immuno-epidemiological model and applied it to longitudinal data of two gastrointestinal helminths in two rabbit populations to investigate, through model testing, how immune-mediated mechanisms of parasite regulation could explain the higher intensities of both helminths in rabbits with dual than single infections. The model framework was selected and calibrated on rabbit population A and then validated on the nearby rabbit population B to confirm the consistency of the findings and the generality of the mechanisms. Simulations suggested that the higher intensities in rabbits with dual infections could be explained by a weakened or low species-specific IgA response and an asymmetrical IgA cross-reaction. Simulations also indicated that rabbits with dual infections shed more free-living stages that survived for longer in the environment, implying greater transmission than stages from hosts with single infections. Temperature and humidity selectively affected the free-living stages of the two helminths. These patterns were comparable in the two rabbit populations and support the hypothesis that immune-mediated facilitation can contribute to greater parasite fitness and local persistence.

Arthurdendyus triangulatus (Dendy, 1894) is a land planarian native to New Zealand which has become established in the United Kingdom and the Faroe Islands during the last 60 years. The species has become prevalent and widely established in Scotland mediated by human activity mostly through the exchange of plants and associated soil. As a predator of earthworms, concerns regarding both the direct impact on earthworm abundance and diversity and the indirect impact on those birds and mammals that have earthworms as a primary dietary component led to A. triangulatus being the subject of both national and EU regulation. Whilst much is known regarding the ecology of A. triangulatus there is a significant knowledge gap regarding the genetic variability of the species. Using four DNA target regions cytochrome oxidase (CoI), elongation factor (EF), internal transcribed spacer region (ITS-1) and large subunit (LSU), we characterised the genetic variability of A. triangulatus populations across its full geographic range in Scotland and included a few populations from New Zealand, England and Northern Ireland. Two DNA regions, ITS-1 and CoI, revealed inter-population variability yielding well supported genetic structure in predominantly Scottish populations. We also identified considerable intra-specific and intra-individual heterogeneity in both ribosomal and mitochondrial regions, including the prevalence of pseudo-gene nuclear encoded mitochondrial DNA (Numt), the latter not previously reported for Platyhelminthes. Furthermore, given the presence of multiple ITS-1 haplotypes in individual specimens of A. triangulatus it is not possible to make definitive comment to support previously published findings that A. triangulatus was subjected to multiple introductions into the UK.

The myxoma virus (a microparasite) reduced wild rabbit numbers worldwide when introduced in the 1950s, and is known to interact with co-infecting helminths (macroparasites) causing both increases and decreases in macroparasite population size. In the 1990s Rabbit Haemorrhagic Disease Virus (RHDV) infected rabbits and also significantly reduced rabbit numbers in several countries. However, not much is known about RHDV interactions with macroparasites. In this study, we compare prevalence and intensity of infection for three gastrointestinal nematode species (Trichostrongylus retortaeformis, Graphidium strigosum and Passalurus ambiguus) before and after RHDV spread across host populations in Scotland and New Zealand. During one common season, autumn, prevalence of T. retortaeformis was higher after RHDV spread in both locations, whereas it was lower for G. strigosum and P. ambiguus after RHDV arrived in New Zealand, but higher in Scotland. Meanwhile, intensity of infection for all species decreased after RHDV arrived in New Zealand, but increased in Scotland. The impact of RHDV on worm infections was generally similar across seasons in Scotland, and also similarities in seasonality between locations suggested effects on infection patterns in one season are likely similar year-round. The variable response by macroparasites to the arrival of a microparasite into Scottish and New Zealand rabbits may be due to differences in the environment they inhabit, in existing parasite community structure, and to some extent, in the relative magnitude of indirect effects. Specifically, our data suggest that bottom-up processes after the introduction of a more virulent strain of RHDV to New Zealand may affect macroparasite co-infections by reducing the availability of their shared common resource, the rabbits. Clearly, interactions between co-infecting micro- and macroparasites vary in host populations with different ecologies, and significantly impact parasite community structure in wildlife., Graphical abstract Image 1, Highlights • Nematode communities in Scotland and New Zealand were compared pre and post Rabbit Haemorrhagic Disease Virus introduction. • Similar species occur in both rabbit populations, but prevalence and intensity changed in opposing directions after RHDV. • RHDV had a major impact on rabbit populations, and our data show differing impacts on macroparasites in the two countries. • Variability in rabbit environment, parasite community structure, and indirect interaction processes may explain differences. • Results can help understand interactions between co-infecting parasites and their epidemiology in wild and domestic animals.

Comment article.

SUMMARYIn wild rabbits (Oryctolagus cuniculus) on an estate in Perthshire, central Scotland, the seroprevalence ofToxoplasma gondiiwas 18/548 (3·3%). The wild rabbit could be aT. gondiireservoir and it has potential value as a sentinel ofT. gondiiin environmental substrates.Toxoplasma gondiiwas associated with female sex (P< 0·001) and with relatively heavy infections byEimeria stiedae(P= 0·036). It was not associated with the intensity of coccidial oocysts, the severity of myxomatosis caused by the virusMyxomatosis cuniculi, the intensity of roundworm eggs, the year or season, rabbit age or distance from farm buildings. Coinfections could have been affected by gestational down regulation of type 1 T helper cells. A sudden influx or release ofT. gondiioocysts might have occurred. This is the first report ofT. gondiiin any wild herbivore in Scotland and also the first report of lapineT. gondiias a coinfection withE. stiedae, M. cuniculiand helminths.

Urbanisation and agriculture dramatically modify the landscapes available for use by wildlife, affecting key aspects of their ecology such as survival, foraging, predation, competition and reproductive success. Relatively little is known about the effects of urbanisation and agriculture on the genetic structure, gene flow and genetic diversity of wild species. Here, landscape genetic techniques were applied to compare local genetic diversity and gene flow between wood mouse populations in urban and arable landscapes. Using nine microsatellite markers, individuals were genotyped from six arable and seven urban sample sites. Inter-population genetic differentiation was significantly greater in urban than arable habitat, while allele richness, private allele richness and heterozygosity were higher for arable sample sites, with varying degrees of significance. These suggest that urban habitat was sufficiently fragmented to limit gene flow. To test the effect of landscape features on gene flow, several cost-distance measures were generated. Overland distance and Euclidean distance correlated best with inter-population genetic differentiation in arable habitat, whereas distances that accommodated differences in habitat quality better explained differentiation in urban habitat. There was no evidence that margins adjacent to roads, rivers or railways facilitated gene flow. Together, the results indicate that urban landscapes expose wood mice to greater fragmentation in habitat quality than arable areas, leading to greater population isolation that is not mitigated by the presence of dispersal corridors.

Small mammal species are abundant and common throughout Europe and often utilise areas that are subject to agricultural land use. Arable farmland is an example of a frequently disturbed habitat, and this study questioned how such disturbance affected the two most common species in the region; one a habitat generalist and one a habitat specialist. We confirmed the prediction that wood mice (Apodemus sylvaticus, a habitat generalist) would make use of a variety of habitats and that bank voles (Myodes glareolus, a habitat specialist) would make greater use of the more stable portions of the study site. We surveyed the study site intensively in order to test whether there was continuity in the spatial arrangement of individuals of both species, given the strategy employed. The spatial arrangement of wood mice varied with season but remained stable for bank voles. We found no association, positive or negative, between the spatial distributions of the two species, suggesting that spatial competitive exclusion did not occur. This work provides further insight into how these small mammal species are affected by agricultural disturbance and predictions can be made about how the species will respond under CAP Reform greening practices.

A study of the epidemiology of myxomatosis and the protozoan liver parasite, Eimeria stiedae, in a population of wild rabbits in Scotland from 1977 to 2010 is reported. Rabbits were collected on a monthly basis resulting in a total of 5,337 animals examined for the infections. The investigation showed that within any 1 year over the 34 years of the investigation the percentage of rabbits with myxomatosis varied between 0 and 24 %, while for E. stiedae infections fluctuated between 3 and 42 %. There were strong seasonal trends in the prevalence of myxomatosis with over 16 % being infected in September and October, and for E. stiedae, peaks of over 40 % of livers infected were recorded in July. From 2007 to 2010, faeces were also examined for coccidia oocysts and parasitic nematode eggs. Rabbits infected with the myxoma virus had mean oocyst counts of 73,665 per gram faeces, while rabbits not infected with the myxoma virus had counts of 31,952 oocysts per gram. Comparable figures for nematode faecal egg counts were 911 per gram in myxomatosis-infected animals and 427 per gram in uninfected animals. The elevated nematode faecal egg counts in rabbits with myxomatosis reflects increased worm burdens already reported, but the elevated counts of coccidial oocysts have not previously been reported. This would suggest that myxomatosis could compromise rabbit immunity to nematodes and coccidia.

SUMMARYThe migration of infective nematode larvae into the tissues of their hosts has been proposed as a mechanism of reducing larval mortality and increase parasite lifetime reproductive success. Given that individual hosts differ in the level of exposure, strength of immune response and physiological conditions we may expect the number of larvae in tissue to vary both between and within hosts. We used 2 gastrointestinal nematode species common in the European rabbit (Oryctolagus cuniculus) and examined how the number of larvae in the tissue changed with the immune response, parasite intensity-dependent constraints in the lumen and seasonal weather factors, in rabbits of different age, sex and breeding status. For both nematode species, larvae from the gastrointestinal tissue exhibited strong seasonal and host age-related patterns with fewer larvae recovered in summer compared to winter and more in adults than in juveniles. The number of larvae of the 2 nematodes was positively associated with intensity of parasite infection in the lumen and antibody responses while it was negatively related with air temperature and rainfall. Host sex, reproductive status and co-infection with the second parasite species contributed to increase variability between hosts. We concluded that heterogeneities in host conditions are a significant cause of variability of larval abundance in the gastrointestinal tissues. These findings can have important consequences for the dynamics of nematode infections and how parasite's life-history strategies adjust to host changes.

Earthworms are important soil organisms yet we have limited knowledge on the geographical distribution of species. Using data from a variety of sources representing a total of 3,941 locality records we have produced the first distribution maps of earthworm species in the British Isles The maps highlight the paucity of knowledge on this ecologically important group. A systematic approach needs to be taken to bring earthworm species data to a level comparable with other important invertebrate groups such as nematodes and isopods. Through the recent establishment of an earthworm recording scheme, the Earthworm Society of Britain, working with the Biological Records Centre and earthworm researchers across the British Isles, aim to build comprehensive distribution information for future monitoring and research purposes.

SUMMARYUnderstanding seasonal changes in age-related incidence of infections can be revealing for disentangling how host heterogeneities affect transmission and how to control the spread of infections between social groups. Seasonal forcing has been well documented in human childhood diseases but the mechanisms responsible for age-related transmission in free-living and socially structured animal populations are still poorly known. Here we studied the seasonal dynamics ofBordetella bronchisepticain a free-living rabbit population over 5 years and discuss the possible mechanisms of infection. This bacterium has been isolated in livestock and wildlife where it causes respiratory infections that rapidly spread between individuals and persist as subclinical infections. Sera were collected from rabbits sampled monthly and examined using an ELISA. Findings revealed thatB. bronchisepticacirculates in the rabbit population with annual prevalence ranging between 88% and 97%. Both seroprevalence and antibody optical density index exhibited 1-year cycles, indicating that disease outbreaks were seasonal and suggesting that long-lasting antibody protection was transient. Intra-annual dynamics showed a strong seasonal signature associated with the recruitment of naive offspring during the breeding period. Infection appeared to be mainly driven by mother-to-litter contacts rather than by interactions with other members of the community. By age 2 months, 65% of the kittens were seropositive.

Serum and liver samples collected monthly, during 2005, from healthy wild rabbits at a site in Pitroddie, Scotland, were analysed by ELISA and RT-PCR sequencing. Sera collected in January and February had high antibody titres against RHDV. However, during the rabbit breeding season average antibody titres were lower but increased again as the year progressed. Between March and August, RHDV-specific RNA was detected in healthy rabbits spanning a wide range of age and antibody titres. Importantly, two virus lineages were identified; a novel widely divergent strain, recovered between March and August, and a strain related to UK epidemic strains, was recovered between May and July from juvenile rabbits. We propose that a non-virulent widely divergent strain of RHDV circulated asymptomatically amongst the wild rabbits potentially inducing immunity against the introduced epidemic strain that predominantly causes high fatality rates in young immunologically naïve rabbits.

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-gamma locus on chromosome 3. Although the causative mutations are still unknown both genes are plausible candidates.

Global climate change is predicted to alter the distribution and dynamics of soil-transmitted helminth infections, and yet host immunity can also influence the impact of warming on host–parasite interactions and mitigate the long-term effects. We used time-series data from two helminth species of a natural herbivore and investigated the contribution of climate change and immunity on the long-term and seasonal dynamics of infection. We provide evidence that climate warming increases the availability of infective stages of both helminth species and the proportional increase in the intensity of infection for the helminth not regulated by immunity. In contrast, there is no significant long-term positive trend in the intensity for the immune-controlled helminth, as immunity reduces the net outcome of climate on parasite dynamics. Even so, hosts experienced higher infections of this helminth at an earlier age during critical months in the warmer years. Immunity can alleviate the expected long-term effect of climate on parasite infections but can also shift the seasonal peak of infection toward the younger individuals.

During the past 50 years two readily distinguishable rabbit-specific diseases caused by Myxoma virus (MYXV) and Rabbit haemorrhagic disease virus (RHDV) respectively, have decimated wild rabbit populations worldwide. Combined with the use of these viruses as biocontrol agents, the consequences for farming, commercial rabbit breeding and rare habitat conservation dependent on rabbit grazing, have been both positive and negative. Moreover, rare predators that rely on rabbits as a food resource, and even hunters, have suffered the consequences of rabbit populations being affected by one or other of these viruses. Rabbit haemorrhagic disease virus was first identified after thousands of domestic rabbits died suddenly in China in 1984. Similar epidemics subsequently occurred in other regions of Asia, the Middle East, Europe and North America, suggesting that the virus had dispersed widely following its emergence in China. However, the discovery that RHDV had circulated apparently harmlessly for many years before the first recognised epidemic in China prompted us to investigate the evolution, emergence and dispersal of this virus in relation to its impact on conservation of wildlife species. Accordingly, we have sequenced new isolates of RHDV and combined these data with a global selection of available RHDV sequences. Using phylogenetic analysis we demonstrate that the Chinese epidemic virus diverged from European viruses that circulated many years prior to 1984. We also demonstrate that the lineages of the pathogenic viruses that emerged in the UK in the early 1990s, are distinct from and pre-date those of the 1984 Chinese virus. In other words, European strains of RHDV emerged from apparently harmless strains to cause epidemic outbreaks, independently of the Chinese 1984 epidemic virus. These studies demonstrate how understanding viral epidemiology can improve the development of strategies to conserve rabbits, rare predator species and the habitat.

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 parasite's 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.

Many studies of the population dynamics of the planarian Arthurdendyus triangulatus have been confounded because it has not been possible to define if small flatworms are adults that have been starved or young ones being recruited into the population. Body shrinkage is a process exhibited by planarians under nutritional stress. In birds and the few invertebrate species studied, starvation leads to a 15N-enrichment of body tissues (i.e. an increased δ15N). Under laboratory conditions, the posterior parts of flatworms were removed at day 0 and frozen and compared isotopically with the anterior parts of flatworms, which were starved for 67, 108, 171 and 243 days. With one exception, δ13C 108 days after starvation, the impact of starvation on A. triangulatus %N, %C and δ13C was not significant statistically. In contrast, δ15N increased significantly (to a maximum enrichment of 2.8‰ by day 243) on all sampling dates. This is supported by significant positive correlations between the changes in δ15N between the anterior and posterior body parts and number of days after starvation (p≤0.05) and decrease in body weight (p≤0.01), respectively. Existing δ15N data from field populations of animals show intra-population variability of around 5.0‰, greater than that noted as a result of starvation. Thus, as a single measure, it is unlikely that δ15N can be used to accurately characterise the proportion of starved A. triangulatus within a field population.

Abstract To seek unifying principles underlying adult body size in the phylum Nematoda, the volume of females of 3150 nematode species in 186 genera has been calculated from published length and diameter information; genera are grouped using the rDNA-based clades of De Ley et al. While the mass of females in some of the clades overlap, there are usually distinct differences within any particular clade between those nematodes that exist in living substrates and those that do not, the latter invariably being smaller. In all five clades (but not Chromadorida) the ability for females to achieve relatively great size is normal, but diminutive females are known from most clades and habitats. Bacterial feeding is common in females in non-living substrates and related females in living substrates, which may represent alternate generations, are often larger. If both groups of females are bacterial feeding it would help to understand the conundrum of whether those in living substrates are larger because they utilise better physical conditions or are larger because they are required to produce more propagules. Female body volume has previously been successfully used in zoogeography and further investigations may include not only adult volume but also address the question of stage-to-stage growth for which earlier studies revealed a paucity of data. This survey of the phylum has not been controlled for phylogeny, apart from the use of clades, and detailed studies could be made within clades. In particular, the effect of substrate, controlled through using species with alternate life cycles, should be tractable.

We assessed the effect of two pathogens (myxoma virus and Eimeria stiedae) and five macroparasites (gastrointestinal helminth species) of the wild rabbit (Oryctolagus cuniculus) upon total host body mass and abdominal fat level. Additionally, we assessed the effects of these organisms on the number of foetuses in adult females during the peak breeding period. Both mass of abdominal fat and total body mass of the rabbit were negatively associated with myxoma virus infection and increasing helminth species richness. Total body mass was also negatively associated with the protozoan parasite E. steidae. No relationship was found between any of the parasites/pathogens and the number of foetuses in adult females, although only relatively small sample sizes were available for this section of the analysis. Increasing host body mass was positively associated with number of foetuses and we propose that mass reduction caused by the pathogen and parasite species could also have the consequence of reducing foetal number.

The New Zealand flatworm (Arthurdendyus triangulatus), which is an obligate predator of native earthworms, is an alien species to the British Isles and is widely distributed in Scotland. What little is known about its biology under field conditions is mainly from Northern Ireland. Samples taken from single sampling dates have shown A. triangulatus to have an aggregated distribution. To determine the spatio-temporal distribution of A. triangulatus, a grass field in western Scotland was intensively sampled over a 16-month period. Data indicate an increase in flatworm numbers and seasonal trends in body weight, the appearance of egg capsules and hatchlings. Results also showed that spatially, the flatworms were aggregated, but this was a transient phenomenon over the period of the experiment. The distribution of egg capsules in the study area was strongly aggregated and related to the appearance of hatchlings. Flatworms may aggregate in areas where soil moisture is optimal for the survival of the New Zealand flatworm.

Natural abundances of the stable isotopes,15N/14N (δ15N) and13C/12C (δ13C), were used to study temporal host-parasite relationships of the wild rabbit,Oryctolagus cuniculus(L.). During the 12-month sampling period, temporal isotopic shifts in δ15N were noted for dietary vegetation, host rabbit faeces and fur, but not for muscle or stomach contents. δ15N varied temporally for the parasitic cestode species,Mosgovoyia pectinatabut not forCittotaenia denticulata. Similarly, intestinal parasitic nematodes had apparent species-specific δ15N patterns. Only rabbit fur and intestinal parasitic nematodes did not exhibit temporal shifts in δ13C. Overall, host faeces and stomach contents were isotopically indistinct as a likely consequence of coprophagy. Relative to their host, parasitic nematodes were15N-enriched, consistent with an increase in trophic level status. Conversely, cestodes were15N-depleted. Isotopically, each parasite reflected a species-specific relationship with their rabbit host. This technique could be utilized to integrate parasites into food-web studies.

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.

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.

To seek unifying principles underlying growth patterns in the phylum Nematoda, the volume of successive developmental stages was determined from published measurements. Within some groups occupying fairly uniform, non-living habitats ( e.g. , Longidoridae, Mononchida, non-parasitic Rhabditida) growth patterns are similar, as are the sizes of both sexes. In aquatic Chromadorida and Monhysterida, females are commonly larger than males. Plant-parasitic groups vary in the relative size of the sexes; within Criconematoidea there is some reduction of males in Hemicyliophora but extreme reduction in Tylenchulus. Despite freeliving and parasitic cycles of Strongyloides showing differing growth in stages 2 to 4, females are similar in both cycles. The strongylid parasites of vertebrates studied have a bacterial-feeding external stage and have lower growth rates and achieve smaller female size than Ascardia with direct life cycles. In taxa for which data are available, the increase in volume between stages 1 and 2 was 0.4-53-fold; that between stages 2 and 3, typically, 1.8-2.9-fold but up to 8191-fold; between stages 3 to 4, 1.7-3.8-fold but up to 100-fold; and between stage 4 to female, typically, 1.1-42-fold but up to 918-fold. Complete data are available for few nematode species and there is no apparent consistent pattern in which taxa contain 'outliers' at particular stages. Many more data are required to assess the impacts of habitat texture, physical support, food supply and experienced temperature on nematode growth and size.

There are few data on the functional inter-relationships between above- and below-ground components of soil ecosystems. Here, we report changes in below-ground soil invertebrate trophic relationships (manifested as alterations in stable isotope natural abundances, d 13 C and d 15 N) that arose in association with the removal of sheep grazing and from the resulting changes in above-ground floristic composition. Consequent to grazing removal, Lolium perenne L. (perennial rye-grass) was replaced as the dominant plant species in ungrazed treatments by Ranunculus repens L. (creeping buttercup), a species with more 13 C-enriched foliage. Consequently, all invertebrate functional groups studied, but not whole soil, were more 13 C-enriched in ungrazed treatments. Earthworms (detritivore) from grazed treatments were significantly 15 N-enriched compared with earthworms from ungrazed treatments. In contrast, slug (herbivore) d 15 N exhibited no treatment effect. Reasons for this are unclear but may be related to the effects of above-ground grazing on the composition of below-ground microbial/microfaunal communities. Omnivores/carnivores (beetles and spiders), were more 15 N-enriched than primary producers in the grazed than in the ungrazed treatments (6 vs. 4‰) suggesting a longer below-ground foodchain in the grazed plots. The cessation of fertilizer application had no comparable effects on below-ground trophic relationships. q 2002 Elsevier Science Ltd. All rights reserved.

To investigate changes in body size of Longidoridae during growth, we used published dimensions of stages to calculate volumes of the juvenile and adult stages of 33 species. A consistent increase in body volume between the juvenile stages was found with proportionally more growth occurring between the smaller stages. In species where three, rather than four, juvenile stages are present, the ultimate size of adults was correspondingly smaller. In the Heteroderidae, greatest growth occurs in later stages and this indicates different adaptations to plant parasitism. Analysis of further groups of free-living and parasitic nematodes is required to increase understanding of body growth and life histories, both within and between families.

Given the health and economic burden associated with the widespread occurrence of co-infections in humans and agricultural animals, understanding how coinfections contribute to host heterogeneity to infection and transmission is critical if we are to assess risk of infection based on host characteristics. Here, we examine whether host heterogeneity to infection leads to similar heterogeneity in transmission in a population of rabbits single and co-infected with two helminths and monitored monthly for eight years. Compared to single infections, co-infected rabbits carried higher Trichostrongylus retortaeformis intensities, shorter worms with fewer eggs in utero, and shed similar numbers of parasite eggs. In contrast, the same co-infected rabbits harbored fewer Graphidium strigosum with longer bodies and more eggs in utero, and shed more eggs of this helminth. A positive density-dependent relationship between fecundity and intensity was found for T. retortaeformis but not G. strigosum in co-infected rabbits. Juvenile rabbits contributed to most of the infection and shedding of T. retortaeformis, while adult hosts were more important for G. strigosum dynamics of infection and transmission, and this pattern was consistent in single and co-infected individuals. This host-parasite system suggests that we cannot predict the pattern of parasite shedding during co-infections based on intensity of infection alone. We suggest that a mismatching between susceptibility and infectiousness should be expected in helminth coinfections and should not be overlooked.

Microbial communities differing in biodiversity were established by inoculating sterile agricultural soil with serially diluted soil suspensions prepared from the parent soil. Three replicate communities of each dilution were allowed to establish an equivalent microbial biomass by incubation for 9 months at 15°C, after which the biodiversity–ecosystem function relationship was examined for a range of soil processes. Biodiversity was determined by monitoring cultivable bacterial and fungal morphotypes, directly extracted eubacterial DNA and protozoan taxa. In the context of this study biodiversity relates to the numbers and proportions of different microbial species. Biodiversity decreased by ca. 15, 40 and 60% at each successive dilution step. There was no consistent effect of biodiversity on a range of soil processes measured (incorporation of thymidine and leucine, potential nitrification, nitrate accumulation, respiratory growth response, community level physiological profile and decomposition). Neither was there a direct effect of biodiversity on the variability of the processes, nor on the stability of decomposition when the soils were perturbed by heat or copper. The biodiversity of, and inter-relationships within, the microbial communities was such that the experimental reductions had no direct effects on soil function.

The New Zealand flatworm Arthurdendyus triangulatus (=Artioposthia triangulata) is an example of an invasive organism that, by reducing lumbricid earthworm populations, could have a major impact on soil ecosystems in Britain and the Faroe Islands. How it was introduced into the British Isles is not known, but like many invasive species, it is suspected that it was introduced by humans and was associated with the trade between New Zealand and Britain. Once established in Britain it found in the large, readily available earthworm population a niche that it could exploit. The microclimate of the forests in the center and south of the South Island of New Zealand from whence the flatworm came is similar to that in parts of the British Isles and consequently conducive to its survival. Although when compared with many other invertebrate introductions (e.g., insects) the flatworm's rate of increase has been slow, a retrospective study strongly suggested that, in Scotland, they spread from botanic gardens to horti...

Summary Earthworm populations from 200 fields (132 pasture and 68 arable) in Scotland are compared. Earthworms populations from two pasture fields at a Scottish farm infested with the New Zealand terrestrial planarian, Arthurdendyus triangulates (a predator of earthworms), are compared with a subset of these 200 fields (none of which had planarians at the time of the survey). A variety of univariate and multivariate methods are used for comparison. Results from the 200 fields show that the number of individuals, number of species, richness and diversity decline eastwards and northwards across Scotland. There is an overall difference between pasture and arable fields at the same farm, with fewer anecic earthworms (Aporrectodea longa and Lumbricus terrestris), but more Aporrectodea rosea, in arable fields. Conversely, species richness and cumulative species diversity is greater in arable fields, and sample similarity is less. The planarian-infested fields show differences from the subset of western Scottish pasture fields and from each other. Both have fewer Aporrectodea caliginosa (and endogeic total) and A. longa (and anecic total) than the western pasture fields. One field has fewer L. terrestris and fewer earthworms in total. Univariate factors show no significant differences between the infested fields and similar non-infested fields, but multivariate analysis suggests differences. Waterlogging and recent growth of rushes in the infested fields are discussed in relation to the reduced population of earthworms and to rainfall.

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.

Seven criconematid species: Ogma menzeli, Criconema annuliferum, C. princeps, Criconemoides pleriannulatus, Mesocriconema solivagum, M. xenoplax and Xenocriconemella macrodora were recovered from soil samples collected from oak forests in the Shulgan-Tash and Voronezh nature reserves in Russia. Examination of C. pleriannulatus by SEM confirmed the absence of submedian lobes and revealed the presence of a small lip annule; juveniles exhibit fringe-like cuticular ornamentation of the annules. Ogma menzeli and C. pleriannulatus are new geographical records for Russia, and all species have already been reported in association with different oak species with the exception of M. solivagum and C. pleriannulatus. Criconemoides mutabilis Eroshenko, 1980 is proposed as a junior synonym of C. pleriannulatus Ebsary, 1979.

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.

Experiments to assess the impact of the different management regimes were undertaken at a number of experimental farms in England. Soil samples taken from these sites were examined for nematodes in 1989, 1992 and 1994. The data indicated that of the four treatments, natural regeneration, sown ryegrass, sown ryegrass/clover and arable cropping, none had any consistent significant effect on the nematode populations over all the three sites. Plant-parasitic nematodes increased in numbers in all treatments at all sites between 1989 and 1994 as did those of most non-plant parasitic species while predatory nematode populations tended to increase in 1992 and decrease again in 1994. The results, which allowed comparisons to be made between sites, seasons and treatments, suggest that the land returning to conventional tillage after years in set-aside would not have a markedly different plant parasitic nematode problem than those continuing in a conventional arable rotation.

Summary. Plant-parasitic nematodes were monitored in the multidisciplinary TALISMAN (Towards a Lower Input System Minimising Agrochemicals and Nitrogen) experiment undertaken at ADAS experimental sites at Boxworth, Drayton and High Mowthorpe, England (1990–1994). The treatments compared standard and alternative rotations, reduced and full herbicide application and full and half rate nitrogen at all three sites. After 6 yr, results snowed no evidence of either a positive or negative impact of the reduced application of agrochemicals on the non-target plant-parasitic nematode populations. Greatest differences were the unexplained year to year variability in nematode numbers.

A review of the literature on nematode diversity (=number of species identified) of soil inhabiting nematodes was undertaken and analysed with regard to distance from the equator, vegetation type and sampling effort. After applying a correction factor for sampling effort the results indicated that species richness was greatest in temperate broadleaf forest (61.7 species per sample) followed by cultivated soil, grassland, tropical rainforest, temperate coniferous forests and polar vegetation. The maintenance of high biodiversity in cultivated soils is unexpected but may reflect the impact of dominance in calculating many indices. Species richness was greatest between latitudes 30–40° (93.9 species per sample) and least above 70°, the mean richness near the equator (i.e. 0–10°) was 80.6 species per sample. While these data would suggest that nematode diversity is not necessarily greatest at the equator, and evidence to support a 'humped back' theory of species richness is not conclusive, they contradict the suggestion that nematode diversity increases with increased latitude.

A study of type material of Jensenonchus sphagni (Brzeski, 1960) n. comb. and Jensenonchus vorax (Cobb, 1917) Andrassy, 1993 confirmed the validity of J. sphagni. Examination of specimens recorded as Mulveyellus vorax (Cobb, 1917) Siddiqi, 1984 from Scotland, revealed that they were J. sphagni. Both species have been found only in moist natural or semi-natural habitats, often associated with mosses. The geographical distribution of J. vorax seems to be restricted to North America whereas J. sphagni apparently occurs only in Europe, thus, these two nematodes are rare examples of vicariant nematode species.

The spatial distributions of three nematode species (Longidorus elongatus, Longidorus goodeyi and Rotylenchus goodeyi) were intensively sampled in a permanent pasture field. Three regular sampling grids were employed covering scales ranging from 5 cm to 50 m. Geostatistical analyses were used to quantify any spatial dependencies found within and between nematode species. All three species were present in most samples and in general the raw counts were positively skewed. Semivariograms of transformed counts (log 10 (counts + 1)), showed similar, generally isotropic, trends for all three species with the variance increasing with separation distance. There was no evidence of a sill i.e. a levelling off of variance at larger scales. The only inter-species correlations detected were at scales up to about 20 cm between L. elongatus and L. goodeyi, species which share a similar environmental niche. A power model provided the best description of the semivariograms and is discussed in relation to "fractional Brownian motion", a scaling property present in many natural systems.

Using published records for the widespread, polyphagous, plant-parasitic nematode Paratrichodorus minor and the 'match climates' function of the computer model CLIMEX, we assessed the impact of a 2°C increase in mean annual temperature. Best current distribution records are from eastern Australia and South Africa (26 and 24 respectively). CLIMEX demonstrates a shift in the range of P. minor in Australia and Africa in response to climate warming. The actual changes are dependent on local interactions between topography and climate. With the available data it is reasonable to consider that similar changes in range would occur elsewhere on the globe. The new distribution would be affected by other environmental conditions and any climate-related changes in them.