Örjan Östman

Host specificity in avian blood parasites: a study of Plasmodium and Haemoproteus mitochondrial DNA amplified from birds

A fragment of the mitochondrial cytochrome b gene of avian malaria (genera Haemoproteus and Plasmodium) was amplified from blood samples of 12 species of passerine birds from the genera Acrocephalus, Phylloscopus and Parus. By sequencing 478 nucleotides of the obtained fragments, we found 17 different mitochondrial haplotypes of Haemoproteus or Plasmodium among the 12 bird species investigated. Only one out of the 17 haplotypes was found in more than one host species, this exception being a haplotype detected in both blue tits (Parus caeruleus) and great tits (Parus major). The phylogenetic tree which was constructed grouped the sequences into two clades, most probably representing Haemoproteus and Plasmodium, respectively. We found two to four different parasite mitochondrial DNA (mtDNA) haplotypes in four bird species. The phylogenetic tree obtained from the mtDNA of the parasites matched the phylogenetic tree of the bird hosts poorly. For example, the two tit species and the willow warbler (Phylloscopus trochilus) carried parasites differing by only 0.6%sequence divergence, suggesting that Haemoproteus shift both between species within the same genus and also between species in different families. Hence, host shifts seem to have occurred repeatedly in this parasite-host system. We discuss this in terms of the possible evolutionary consequences for these bird species.

A new nested polymerase chain reaction method very efficient in detecting Plasmodium and Haemoproteus infections from avian blood.

Recently, several polymerase chain reaction (PCR)–based methods for detection and genetic identification of haemosporidian parasites in avian blood have been developed. Most of these have considerably higher sensitivity compared with traditional microscope-based examinations of blood smears. These new methods have already had a strong impact on several aspects of research on avian blood parasites. In this study, we present a new nested PCR approach, building on a previously published PCR method, which has significantly improved performance. We compare the new method with some existing assays and show, by sequence-based data, that the higher detection rate is mainly due to superior detection of Plasmodium spp. infections, which often are of low intensity and, therefore, hard to detect with other methods.

Landscape heterogeneity and farming practice influence biological control

Summary We measured the impact of natural enemies on the population development on the bird cherry-oat aphid ( Rhopalosiphum padi ) on conventional and organic farms. By pairing farms with similar landscape features but different farming systems, we were able to separate the effects of farming practice and landscape features on the influence of natural enemies on R. padi abundance. Natural enemies had a greater impact on R. padi establishment on organic farms than on conventional farms. Irrespective of farming system, landscapes with abundant field margins and perennial crops were associated with low R. padi establishment. After establishment, there was no difference in ground-living enemy impact on R. padi population growth rate between farming systems, but impact was greater in landscapes where arable land was contiguous. Wir untersuchten die Wirkung naturlicher Feinde auf die Populationsentwicklung der Haferblattlaus (Rhopalosiphum padi) in konventionell und organisch bewirtschafteten landwirtschaftlichen Betrieben. Indem wir Betriebe paarten, die ahnliche Landschaftseigenschaften aber unterschiedliche Betriebsformen aufwiesen, konnten wir die Wirkung der Bewirtschaftung und der Landschaftseigenschaften auf den Einflus der naturlichen Feinde auf die Abundanz von R. padi trennen. Die naturlichen Feinde hatten in organisch bewirtschafteten Betrieben eine grosere Wirkung auf die Ansiedlung von R. padi als in konventionell bewirtschafteten Betrieben. Unabhangig von der Bewirtschaftungsform waren Landschaften mit zahlreichen Feldrainen und perennierenden Feldkulturen mit einer geringen Ansiedlung von R. padi verbunden. Die Wirkung bodenlebender Feinde auf die Wachstumsrate der Populationen von R. padi nach der Ansiedlung unterschied sich nicht zwischen den Bewirtschaftungsformen. Die Wirkung war jedoch in Landschaften groser, die zusammenhangende Ackerflachen aufwiesen.

Yield increase attributable to aphid predation by ground-living polyphagous natural enemies in spring barley in Sweden

It has been claimed that natural enemies of pests perform important ecosystem services in agricultural landscapes. These services have rarely been evaluated in yield or monetary terms at farm level. We have examined the degree to which ground-living natural enemies of the bird cherry-oat aphid (Rhopalosiphum padi (L.)) reduced aphid abundance and influenced barley yields on ten commercial farms in central Sweden. On average, ground-living natural enemies of pests increased barley yields by 303 kg/ha. This corresponded to a potential 52% reduction in yield loss from R. padi compared with a scenario where no natural enemies were present. Measured as the percentage increase of actual yield, ground-living natural enemies of aphids increased the yield by 23%. The increase in yields in absolute terms was larger on conventional farms than organic farms, but the percentage increase of yields was larger on organic farms. The study only considered 1 year, with high aphid abundance. However, we also discuss the effects of predators as well as insecticides in the long-term. Our study shows that yield increases attributable to predators can be compared with yield increases from insecticide use for the evaluation of different management strategies.

Species composition in agroecosystems: The effect of landscape, habitat, and farm management

Abstract It has been suggested that species richness in agricultural ecosystems depends on both landscape heterogeneity and farm management, but how these factors affect species composition is still poorly understood. In this study, we investigated the species composition of plants, butterflies, and carabid beetles in three different habitats (cereal fields, leys, and semi-natural pastures) in relation to farm management (conventional vs. organic) and landscape complexity at 16 farms in south-eastern Sweden. The farms were divided into eight pairs of one conventional and one organic farm based on land use, location, and landscape features to enable us to separate the effects of landscape features and farm management on species composition. Habitat type explained most of the variation in species composition of butterflies, carabids, and plants. Landscape features in the surrounding landscape explained additional variation, but little relative to habitat, in species composition. The effect of landscape features was larger in the disturbed habitats (cereal fields and ley) than in the more stable semi-natural pastures. Moreover, the effect of landscape features was largest for the most mobile group, butterflies, and least for the sessile plants. The percentage of ley (land temporarily with perennial grass and clover) was the most important landscape feature for butterfly and plant species composition, whereas landscape heterogeneity was the most important landscape feature for carabid species composition. Farm management explained some additional variation in species composition of carabids and butterflies, but it was of minor importance compared to landscape features for species composition of butterflies and plants. We classified the species as common or rare, but for no taxa were common or rare species associated with any landscape feature or farm management. Es wurde vorgeschlagen, dass der Artenreichtum in Agrarokosystemen sowohl von der Landschaftsheterogenitat als auch von der Bewirtschaftung abhangt. Wie diese Faktoren jedoch die Artenzusammensetzung beeinflussen, wird bisher kaum verstanden. In dieser Arbeit untersuchten wir in 16 landwirtschaftlichen Betrieben im sudostlichen Schweden die Artenzusammensetzung von Pflanzen, Schmetterlingen und Laufkafern in drei verschiedenen Habitaten (Getreidefelder, Graslandern, und seminaturlichen Weiden) im Zusammenhang mit der Bewirtschaftung (konventionell vs. organisch) und der Landschaftskomplexitat. Basierend auf Landnutzung, Ort, und Landschaftselementen wurden die Betriebe in acht Paare mit je einem konventionellen und organischen Betrieb unterteilt, um uns zu ermoglichen, die Effekte der Landschaftselemente und der Bewirtschaftungsform zu trennen. Der Habitattyp erklarte den grosten Anteil der Variation in der Artenzusammensetzung bei den Schmetterlingen, Laufkafern und Pflanzen. Die Landschaftselemente der umgebenden Landschaft erklarten die Variation in der Artenzusammensetzung zusatzlich, im Verhaltnis zum Habitat jedoch nur in geringem Ausmas. Der Effekt der Landschaftselemente war in gestorten Habitaten (Getreidefelder und Graslander) groser als in den stabileren semi-naturlichen Weiden. Die Effekte der Landschaftselemente waren zudem am Grosten fur die mobilste Gruppe, die Schmetterlinge, und am Geringsten fur die sessilen Pflanzen. Der Anteil des Graslands (Land, zeitweise mit perennierendem Gras und Klee bestanden) war das wichtigste Landschaftselement fur die Schmetterlings- und Pflanzenartenzusammensetzung, wahrend Landschaftheterogenitat das wichtigste Landschaftselement fur die Laufkaferartenzusammensetzung war. Die Bewirtschaftungsform erklarte ein wenig der zusatzlichen Variation in der Artenzusammensetzung der Laufkafer und Schmetterlinge, war aber im Vergleich zu den Landschaftselementen von geringer Bedeutung fur die Artenzusammensetzung der Schmetterlinge und Pflanzen. Wir klassifizierten die Arten als verbreitet oder selten, aber bei keinem Taxon waren verbreitete oder seltene Arten mit irgendeinem Landschaftselement oder einer Bewirtschaftungsform assoziiert.

LANDSCAPE COMPLEXITY AND FARMING PRACTICE INFLUENCE THE CONDITION OF POLYPHAGOUS CARABID BEETLES

Previous work has suggested that the condition of polyphagous predatory carabid beetles can be influenced by landscape structure and farming practice. However, earlier studies aimed at testing the effect of farming practice on insect condition and reproduction have not been designed to test this accurately because farms representing different cultivation systems have not had similar landscape complexity. In this study we measured the condition of the polyphagous predatory carabid beetles Harpalus rufipes, Pterostichus cupreus, P. melanarius, and P. niger from five pairs of conventional and organic farms in central east Sweden. The farms within each pair were near to each other and had similar size, land use, and landscape structure. The condition of the beetles was measured as the residuals from the regression between ln(elytra length) and ln(body mass). We show that the residuals for P. melanarius were positively correlated with their fat reserves. For P. melanarius, residuals were higher on farms where the fields had high perimeter-to-area ratio. The pooled residuals of H. rufipes, P. cupreus, and P. niger were positively correlated with the perimeter-to-area ratio and crop diversity. Pterostichus me- lanarius from organic farms had better condition than conspecifics at conventional farms, and for H. rufipes, P. cupreus, and P. niger combined there was a tendency toward better condition on organic farms than at conventional farms. Harpalus rufipes, P. cupreus, P. melanarius, and P. niger, which are all polyphagous predatory carabid beetles, are natural enemies of pest aphids in the agroecosystem. We conclude that, by manipulating landscape structure and composition, improvement in the condition of polyphagous predatory carabid beetles could be achieved, thereby potentially increasing populations of these beneficial insects.

Regional invariance among microbial communities

Microbial ecology has focused much on causes of between-site variation in community composition. By analysing five data-sets each of aquatic bacteria and phytoplankton, we demonstrated that microbial communities show a large degree of similarity in community composition and that abundant taxa were widespread, a typical pattern for many metazoan metacommunities. The regional abundance of taxa explained on average 85 and 41% of variation in detection frequency and 58 and 31% of variation in local abundances for bacteria and phytoplankton, respectively. However, regional abundance explained less variation in local abundances with increasing environmental variation between sites within data-sets. These findings indicate that the studies of microbial assemblages need to consider similarities between communities to better understand the processes underlying the assembly of microbial communities. Finally, we propose that the degree of regional invariance can be linked to the evolution of microbes and the variation in ecosystem functions performed by microbial communities.

Which sequencing depth is sufficient to describe patterns in bacterial α- and β-diversity?

The vastness of microbial diversity implies that an almost infinite number of individuals needs to be identified to accurately describe such communities. Practical and economical constraints may therefore prevent appropriate study designs. However, for many questions in ecology it is not essential to know the actual diversity but rather the trends among samples thereof. It is, hence, important to know to what depth microbial communities need to be sampled to accurately measure trends in diversity. We used three data sets of freshwater and sediment bacteria, where diversity was explored using 454 pyrosequencing. Each data set contained 6-15 communities from which 15 000-20 000 16S rRNA gene sequences each were obtained. These data sets were subsampled repeatedly to 10 different depths down to 200 sequences per community. Diversity estimates varied with sequencing depth, yet, trends in diversity among samples were less sensitive. We found that 1000 denoised sequences per sample explained to 90% the trends in β-diversity (Bray-Curtis index) among samples observed for 15 000-20 000 sequences. Similarly, 5000 denoised sequences were sufficient to describe trends in α-diversity (Shannon index) with the same accuracy. Further, 5000 denoised sequences captured to more than 80% the trends in Chao1 richness and Pielous evenness.

Temporal variation of β-diversity and assembly mechanisms in a bacterial metacommunity

The turnover of community composition across space, β-diversity, is influenced by different assembly mechanisms, which place varying weight on local habitat factors, such as environmental conditions and species interactions, and regional factors such as dispersal and history. Several assembly mechanisms may function simultaneously; however, little is known about how their importance changes over time and why. Here, we implemented a field survey where we sampled a bacterial metacommunity consisting of 17 rock pools located at the Swedish Baltic Sea coast at 11 occasions during 1 year. We determined to which extent communities were structured by different assembly mechanisms using variation partitioning and studied changes in β-diversity across environmental gradients over time. β-Diversity was highest at times of high overall productivity and environmental heterogeneity in the metacommunity, at least partly due to species sorting, that is, selection of taxa by the prevailing environmental conditions. In contrast, dispersal-driven assembly mechanisms were primarily detected at times when β-diversity was relatively low. There were no indications for strong and persistent differences in community composition or β-diversity between permanent and temporary pools, indicating that the physical disturbance regime is of relatively minor importance. In summary, our study clearly suggests that there are temporal differences in the relative importance of different assembly mechanisms related to abiotic factors and shows that the temporal variability of those factors is important for a more complete understanding of bacterial metacommunity dynamics.

The importance of dispersal for bacterial community composition and functioning.

We conducted a metacommunity experiment to investigate the role of dispersal for bacterial community composition (BCC) and function of freshwater bacteria. Bacteria were dispersed from a common source pool into three different lake communities in their natural lake water. The experiment was conducted in dialysis bags to enable a decoupling between a change in the local environment and dispersal. BCC was determined by terminal restriction fragment length polymorphism (tRFLP) of the 16S rRNA gene. We show that the greatest changes in BCC occurred between 10% and 43% of dispersal of standing stock per day. Functioning, measured as growth rate, was also affected by dispersal in all three communities but the qualitative pattern differed between communities, sometimes showing a hump-shaped relationship to dispersal and sometimes decreasing with increasing dispersal. In all waters, functioning was related to BCC. Our results show that dispersal does affect BCC and functioning but that high dispersal rates are needed. Further, the effect of dispersal on BCC and function seem to depend on the quality of the habitat to which bacteria disperse into.