Heteromurus Nitidus Research Articles

Nitidane: An Irregular Prenylated Diterpene from the Cuticle of the Springtail Heteromurus nitidus.

Collembola are closely related to insects, but our knowledge of their often unique chemistry is limited. Here we report the identification of the epicuticular lipid nitidane, representing a novel class of epicuticular lipids. Nitidane (4) is an irregular terpene consisting of seven isoprene units, made up of a diterpene core that is modified by a geranyl moiety that is itself prenylated. The observed [46+(22+11)1]-terpene structure has not been reported before.

The collembolan Heteromurus nitidus grazes the wheat fungal pathogen Zymoseptoria tritici on infected tissues: opportunities and limitations for bioregulation.

Septoria tritici blotch (STB), caused by the fungus Zymoseptoria tritici, is a foliar disease affecting wheat crops against which conventional control methods are not totally effective. During inter-epidemic periods the fungus survives in wheat residues left on the ground. In this study, we tested the potential of the collembolan Heteromurus nitidus - a springtail species present in field soils and known to interact with different fungal species - as a potential bioregulation agent of Z. tritici on wheat residues through a choice and consumption experiment. Springtails preferred inoculated fresh residues but did not have a preference between inoculated and uninoculated old residues. Springtails grazed on Z. tritici fruiting bodies and reduced pycnidiospore numbers by ten-fold compared to control inoculated fresh residues. Attraction toward fresh inoculated residues and pycnidiospore reduction support the hypothesis that Z. tritici is a food source for springtails. Heteromurus nitidus showed no preference between inoculated and uninoculated 18-month-old residues, probably because they no longer produced ascospores. Attraction towards fresh residues and spore reduction support our hypothesis that H. nitidus may contribute to the bioregulation of Z. tritici. Perspectives for field application would be determined by the ability of H. nitidus and Z. tritici to interact at key epidemiological stages. The impact of H. nitidus on the quantity of pathogen primary inoculum over time should be estimated using residues of intermediate age. This would help to identify the optimal period for enhancing the effectiveness of springtails as consumers of Z. tritici. © 2024 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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A personal selection of 32 recent papers is presented covering various aspects of current developments in bioorganic chemistry and novel natural products such as nitidane from Heteromurus nitidus.

Dietary preferences of Heteromurus nitidus (Collembola) among wheat fungal communities: Implications for bioregulation of two widespread pathogens

Soil invertebrates play a key role in agrosystems as providers of several ecosystem services. In particular, they regulate fungal communities in soils and could contribute to mitigate the impact of phytopathogenic fungi overwintering in crop residues. In this study, we investigated the food preferences of Heteromurus nitidus (Collembola) between phytopathogenic and non-pathogenic (or beneficial) fungi present in crop soils and grown in vitro. First, two fungi responsible for the most important diseases of wheat worldwide Zymoseptoria tritici and Fusarium graminearum, and eleven fungi previously served on wheat plants were offered in pathogenic/non-pathogenic pairs to springtails. We showed that Z. tritici was preferred over seven out of the eleven non-pathogenic fungi offered while F. graminearum was only preferred over four of them. Second, we assessed the impact of long-term consumption of these two phytopathogenic fungi by springtails on their population development and assessed how the development of the fungi was affected by the springtails that fed on them. During this long-term experiment, springtails were more abundant in populations fed with phytopathogenic fungus than in control populations after ten weeks. At the end of the experiment, mycelium of both fungi was reduced by springtail activity. These in vitro results suggest a potential of H. nitidus to act as a biological control agent as populations grew when fed on either fungus while reducing fungal development. This point should be confirmed by testing the fungus grown on host plant tissues and with experiments involving interactions with soil and its communities. Z. tritici appears to be a better candidate for such experiments as it was preferred in choice experiments.

New species and records of Entomobryidae and Orchesellidae (Collembola) from the East Caucasus (Russia).

We studied Entomobryidae and Orchesellidae springtails collected throughout Chechnya, Ingushetia, and Dagestan, Russia. Three new species of the genus Entomobrya (E. multisetis sp. nov., E. hirsutothorax sp. nov., and E. kremenitsai sp. nov.), and one of Entomobryoides (E. dagestanicus sp. nov.) are described. Taxonomic information for Entomobrya nicoleti (Lubbock, 1868), Willowsia potapovi Zhang et al., 2011, and Heteromurus nitidus (Templeton, 1836) in Templeton Westwood 1836 from the Caucasus are given.

Protists and collembolans alter microbial community composition, C dynamics and soil aggregation in simplified consumer–prey systems

Abstract. Microbes play an essential role in soil functioning including biogeochemical cycling and soil aggregate formation. Yet, a major challenge is to link microbes to higher trophic levels and assess consequences for soil functioning. Here, we aimed to assess how microbial consumers modify microbial community composition (PLFA markers), as well as C dynamics (microbial C use, SOC concentration and CO2 emission) and soil aggregation. We rebuilt two simplified soil consumer–prey systems: a bacterial-based system comprising amoebae (Acanthamoeba castellanii) feeding on a microbial community dominated by the free-living bacterium Pseudomonas fluorescens and a fungal-based system comprising collembolans (Heteromurus nitidus) grazing on a microbial community dominated by the saprotrophic fungus Chaetomium globosum. The amoeba A. castellanii did not affect microbial biomass and composition, but it enhanced the formation of soil aggregates and tended to reduce their stability. Presumably, the dominance of P. fluorescens, able to produce antibiotic toxins in response to the attack by A. castellanii, was the main cause of the unchanged microbial community composition, and the release of bacterial extracellular compounds, such as long-chained polymeric substances or proteases, in reaction to predation was responsible for the changes in soil aggregation as a side effect. In the fungal system, collembolans significantly modified microbial community composition via consumptive and non-consumptive effects including the transport of microbes on the body surface. As expected, fungal biomass promoted soil aggregation and was reduced in the presence of H. nitidus. Remarkably, we also found an unexpected contribution of changes in bacterial community composition to soil aggregation. In both the bacterial and fungal systems, bacterial and fungal communities mainly consumed C from soil organic matter (rather than the litter added). Increased fungal biomass was associated with an increased capture of C from added litter, and the presence of collembolans levelled off this effect. Neither amoebae nor collembolans altered SOC concentrations and CO2 production. Overall, the results demonstrated that trophic interactions are important for achieving a mechanistic understanding of biological contributions to soil aggregation and may occur without major changes in C dynamics and with or without changes in the composition of the microbial community.

Bringing ecology into toxicology: Life-cycle toxicity of two neonicotinoids to four different species of springtails in LUFA 2.2 natural soil

Collembolans comprise one of the most abundant groups of soil invertebrates within the arthropods. The parthenogenetic species Folsomia candida (Willem, 1902) is the most well-studied representative, being used since the beginning of the 1960s as a model organism for assessing toxicity of chemicals in soil. In this paper we aimed at answering three questions by exposing four different species of springtails (F. candida, Folsomia fimetaria, Sinella curviseta and Heteromurus nitidus) to the neonicotinoids imidacloprid and thiacloprid: i) How representative as a model organism is F. candida for species of springtails that reproduce sexually? (ii) How suitable are other species of springtails to be used as model organisms for ecotoxicological testing? (iii) Is it possible to use the life history of these species to extrapolate the impact of neonicotinoids on the population level? Our results showed that F. candida is a good model organism, despite being the most sensitive species tested, when analysing both endpoints – survival and reproduction. The tests performed with S. curviseta and H. nitidus showed that they could be used as surrogates in ecotoxicity tests, and also to predict how their population might be affected after being exposed to chemicals. The adjustments made to the test performed with F. candida: introducing adults (20–22 days old) into the test jars and exposing them for 21 days instead of 28 days, proved to be as efficient as the standardized test guideline (OECD 232, 2009).

Effect of acidified cattle slurry on a soil collembolan community: A mesocosmos study

The concept of soil health emphasizes the role of soil organisms in sustainable agriculture and relies on bioindicators to assess the impact of management options. This study employed Collembola, a key group of microarthropods with intimate links to soil microbial activity, as bioindicators to reveal the sustainability of using acidified cattle slurry. While environmental and plant production benefits of acidification are well known, effect of acidified slurry on Collembola is undocumented. We added Collembola to sandy soil mixed with untreated or acidified cattle slurry labelled with 15N and applied at two rates (corresponding to 30 and 90 Mg slurry ha−1). The collembolan community included two species for each vertical life-form: epedaphic (Sinella curviseta and Heteromurus nitidus), hemiedaphic (Proisotoma minuta and Hypogastrura assimilis) and euedaphic species (Folsomia fimetaria and Protaphorura fimata). Replicate mesocosmos were incubated for 28 or 56 days at 15 °C, 65% WHC and a 12 h light-dark cycle. The epedaphic species strongly declined at the end of the experiment, whereas P. minuta and F. fimetaria were positively affected by high rates of untreated and acidified slurry, respectively. The hemiedaphic P. minuta showed the highest abundances and accumulation of slurry-15N, especially when high rate of untreated slurry was applied. We conclude that the impact on Collembola of low rates of untreated and acidified slurry applied to agricultural soils is marginal while higher rates of slurry may subsequently form a favourable habitat for euedaphic species.

Fatty Acid 13C Isotopologue Profiling Provides Insight into Trophic Carbon Transfer and Lipid Metabolism of Invertebrate Consumers.

Fatty acids (FAs) are useful biomarkers in food web ecology because they are typically assimilated as a complete molecule and transferred into consumer tissue with minor or no modification, allowing the dietary routing between different trophic levels. However, the FA trophic marker approach is still hampered by the limited knowledge in lipid metabolism of the soil fauna. This study used entirely labelled palmitic acid (13C16:0, 99 atom%) as a tracer in fatty acid metabolism pathways of two widespread soil Collembola, Protaphorura fimata and Heteromurus nitidus. In order to investigate the fate and metabolic modifications of this precursor, a method of isotopologue profiling is presented, performed by mass spectrometry using single ion monitoring. Moreover, the upstream laboratory feeding experiment is described, as well as the extraction and methylation of dominant lipid fractions (neutral lipids, phospholipids) and the related formula and calculations. Isotopologue profiling does not only yield the overall 13C enrichment in fatty acids derived from the 13C labeled precursor but also produces the pattern of isotopologues exceeding the mass of the parent ion (i.e., the FA molecular ion M+) of each labeled FA by one or more mass units (M+1, M+2, M+3, etc.). This knowledge allows conclusions on the ratio of dietary routing of an entirely consumed FA in comparison to de novo biosynthesis. The isotopologue profiling is suggested as a useful tool for evaluation of fatty acid metabolism in soil animals to disentangle trophic interactions.

Isotopologue profiling enables insights into dietary routing and metabolism of trophic biomarker fatty acids

The application of fatty acids (FAs) as biomarkers in food web ecology is based on the concept of dietary routing, i.e., FA assimilation as entire molecule and transfer into consumer tissue with no or minor modification. However, the lack in knowledge in lipid metabolism of the soil fauna hampers the FA trophic marker approach. This study used labeled palmitic acid (13C16:0, 99 atom%) as tracer in lipid pathways of two common soil Collembola, Heteromurus nitidus and Protaphorura fimata. The incorporation and dietary routing of this precursor were determined by 13C:12C FA analysis (gas chromatography–combustion–isotope-ratio-monitoring), while metabolic modifications were assessed with isotopologue profiling (mass spectrometry with single ion monitoring). The 13C enrichment in FAs assigned the transfer of the labeled precursor predominantly into the neutral lipid fraction of Collembola. Thereby, isotopologue profiling demonstrated that dietary routed FAs are marginally metabolically modified. In contrast, the phospholipid fraction showed a considerable degree of FA modification, most markedly a fast degradation of palmitoleic acid. Further, de novo synthesis of linoleic acid was approved for both Collembola species. While 16:0 and 18:0, and their descendants 16:1ω7 and 18:1ω9, followed the concept of dietary routing and thus are good markers, arachidonic acid showed a different metabolism. This comprised elongation/desaturation of 13C16:0 and de novo synthesis, including 13C labeled acetyl-CoA from degradation of the precursor, indicating its utility to assign carbon flow but not as trophic marker. We propose isotopologue profiling as a valuable tool for evaluation of the lipid metabolism in small soil animals to disentangle trophic interactions.

Understanding earthworm – Collembola interactions and their importance for ecosystem processes needs consideration of species identity

Soil animals and their interactions exert strong effects on ecosystem processes, such as leaf litter decomposition and nitrogen (N) cycling, thereby contributing to ecosystem functioning and stability. The understanding of how and why certain species interact is important to predict the effect of soil animal communities on ecosystem processes. Species interactions are discussed as being facilitative, antagonistic or neutral. We investigated interactions between two earthworm (Lumbricus terrestris, Aporrectodea caliginosa) and two Collembola species (Heteromurus nitidus and Protaphorura armata), representing major soil decomposer taxa. The two earthworm species are representatives of the soil macrofauna, with L. terrestris living in permanent vertical burrows and feeding on leaf litter, and A. caliginosa living in non-permanent horizontal burrows and feeding predominantly on resources in organo-mineral soil. The Collembola species are representatives of the soil mesofauna, with H. nitidus predominantly colonizing the soil litter interface and feeding on litter associated resources, whereas P. armata colonizes deeper soil layers and mainly feeds on resources in organo-mineral soil. Therefore, the species were assumed to differ in two major traits, i.e. body size (macrofauna vs. mesofauna) and food microhabitat association (“litter-associated” vs. “soil-associated”). Mesocosms with natural forest floor containing one beech (Fagus sylvatica) sapling were set up and incubated in the laboratory for three months. 15N labeled beech litter was added to follow the effect of detritivore animals on N cycling and N uptake by beech saplings. We hypothesized antagonistic interactions to dominate in species with similar body size or food microhabitat association via hampering the performance (biomass, abundance) of each other thereby reducing effects on leaf litter decomposition and N cycling. On the contrary, we expected species of different body size or food microhabitat association to facilitate each other's effects on ecosystem processes. In contrast to our expectation there was no clear relationship between similarity of body size or food microhabitat association and soil fauna effects on each other. Interactions between detritivores were not consensual with L. terrestris facilitating biomass gain of A. caliginosa, while its own biomass was reduced in presence of A. caliginosa. Additionally, 15N incorporation into A. caliginosa and the two Collembola species decreased in presence of L. terrestris, irrespective of similarity of body size or food microhabitat association. Leaf litter decomposition was increased by L. terrestris, while none of the other species affected litter decomposition. Generally, 15N incorporation into beech saplings was significantly increased in presence of L. terrestris or H. nitidus, but reduced in two species treatments due to antagonistic interactions. Interestingly, it was increased if L. terrestris, A. caliginosa and P. armata were present together, indicating facilitative interactions between these species. The results suggest that soil fauna interactions mainly vary with the identity of species and community composition rather than with similarity of traits. This highlights the complexity of soil fauna interactions and the difficulty to predict their effects on ecosystem processes, such as litter decomposition and N cycling, in species rich communities.

Collembola gut passage shapes microbial communities in faecal pellets but not viability of dietary algal cells

Microarthropods are known as vectors for soil microorganisms, predominantly fungi. This laboratory study uses the widespread unicellular green algae Chlorella vulgaris as model to assess the role of Collembola in algal dispersal and to determine the effects of gut passage on propagation. Living algal cells were observed in 70 % of the faecal pellets of Folsomia candida, Heteromurus nitidus and Protaphorura fimata. Moreover, marker fatty acids for green algae, i.e. 16:2ω6,9 and 16:3ω3,6,9, were consistently detected in the pellets. Compared to the algal diet, the high content of methyl-branched total lipid fatty acid (TLFA) with hydroxyl substitution indicated microbial colonisation during gut passage. The TLFA profile of faeces revealed no species-specific differences but similar changes in microbial communities over the duration of feeding, indicating comparable indigenous bacteria and colonisation mechanisms during gut passage. In sum, faecal pellets of soil microarthropods such as Collembola can act as a vector for both dietary algae and specific gut-associated microorganisms, with the latter likely involved in resource degradation inside and outside the gut habitat.

Arbuscular mycorrhizal fungi and their associated microbial community modulated by Collembola grazers in host plant free substrate

Collembola grazing on arbuscular mycorrhizal fungi (AMF) may affect the transfer of mycorrhizosphere C to the soil food web and the regulation of soil mycorrhizal infectivity potential. We used a plant-free mesocosm experimental system with two different mycorrhizal substrates containing either Glomus deserticola or Gigaspora gigantea and three Collembola species (Heteromurus nitidus, Folsomia candida and Protaphorura fimata) to test the hypothesis that Collembola grazing can interfere directly with AMF feeding on the mycorrhizal propagules and/or indirectly changing structure of associated microbial populations. The fatty acid (FA) composition of Collembola grazers and of their mycorrhizal food substrates was assessed. The feeding strategies of H. nitidus and P. fimata varied distinctly between mycorrhizal substrates, whereas the diet of F. candida was invariant to the presence of mycorrhizal propagules. The FA marker for G. deserticola (16:1ω5) was not detected in Collembola lipids, indicating that this AMF was not consumed. In contrast, H. nitidus and P. fimata comprised the marker for feeding G. gigantea (20:1 ω9). Both mycorrhizal substrates were no profitable diet for H. nitidus, resulting in a decline of individuals. Collembola grazed on the bacterial and fungal populations in the mycorrhizal substrate, predominantly H. nitidus that even decreased microbial biomass, resulting in significant changes in the composition of the microbial community. In sum, grazing by microarthropods can directly and indirectly modulate AMF performance as well as interactions with microorganisms, which in turn can impose on the soil infection potential from AMF propagules.

New trophic biomarkers for Collembola reared on algal diets

We used fatty acid (FA) analysis to investigate green algae and cyanobacteria as food sources for Collembola. We studied the effects of food quality on body mass and on neutral lipid (NLFA) and phospholipid (PLFA) fatty acid patterns of Collembola. Folsomia candida , Heteromurus nitidus and Protaphorura fimata were fed with common green algae ( Chlorella vulgaris ), filamentous soil algae ( Klebsormidium flaccidum ), cyanobacteria ( Nostoc commune ) and baker's yeast ( Saccharomyces cerevisiae ). Body mass of F. candida and H. nitidus was highest when reared on C. vulgaris and S. cerevisiae . P. fimata gained the most weight when fed baker's yeast. K. flaccidum and N. commune as resources resulted to low biomass in all Collembola. The four diets caused significant differences in the NLFA and PLFA composition of Collembola after six weeks of feeding. Two new trophic biomarker FAs indicating algal diets were assigned with 16:3ω3,6,9 and 16:2ω6,9, which were only present in NLFAs of Collembola consuming C. vulgaris and K. flaccidum . The amount of FAs from the ω7 family was high in Collembola lipids with cyanobacteria and yeast as food sources, whereas only trace amounts occurred in the NLFA fraction with algae as the resource. In summary, common soil algae and cyanobacteria differed in food quality for Collembola, depending on their growth form (unicellular versus filamentous) and/or secondary metabolites (e.g. cyanobacteria). The new FA biomarkers detected will allow further investigation of these trophic interactions under field conditions; for example, assessing the role of collembolan grazers in the formation of biological soil crusts.

Soil organisms shape the competition between grassland plant species

Decomposers and arbuscular mycorrhizal fungi (AMF) both determine plant nutrition; however, little is known about their interactive effects on plant communities. We set up a greenhouse experiment to study effects of plant competition (one- and two-species treatments), Collembola (Heteromurus nitidus and Protaphorura armata), and AMF (Glomus intraradices) on the performance (above- and belowground productivity and nutrient uptake) of three grassland plant species (Lolium perenne, Trifolium pratense, and Plantago lanceolata) belonging to three dominant plant functional groups (grasses, legumes, and herbs). Generally, L. perenne benefited from being released from intraspecific competition in the presence of T. pratense and P. lanceolata. However, the presence of AMF increased the competitive strength of P. lanceolata and T. pratense against L. perenne and also modified the effects of Collembola on plant productivity. The colonization of roots by AMF was reduced in treatments with two plant species suggesting that plant infection by AMF was modified by interspecific plant interactions. Collembola did not affect total colonization of roots by AMF, but increased the number of mycorrhizal vesicles in P. lanceolata. AMF and Collembola both enhanced the amount of N and P in plant shoot tissue, but impacts of Collembola were less pronounced in the presence of AMF. Overall, the results suggest that, by differentially affecting the nutrient acquisition and performance of plant species, AMF and Collembola interactively modify plant competition and shape the composition of grassland plant communities. The results suggest that mechanisms shaping plant community composition can only be understood when complex belowground interactions are considered.

Fatty acid patterns as biomarker for trophic interactions: Changes after dietary switch and starvation

Fatty acid (FA) analysis is becoming increasingly important for investigating trophic interactions in soil food webs. FA profiles of neutral lipids are affected by diet, and the occurrence and amount of certain FAs can reflect feeding strategies. However, to draw conclusions on feeding strategies in the field it is necessary to know physiological parameters of fatty acid metabolism such as the detection time and storage period of FAs. In this study we investigated the chronological change of FA biomarkers in the Collembola Heteromurus nitidus when switched between different food sources: leaves (Tilia europaea), a fungus (Chaetomium globosum) and two bacteria (Stenotrophomonas maltophilia, Bacillus amyloliquefaciens). Additionally, we followed the change of bacterial FA biomarkers during starvation. After 14 days of food deprivation bacterial FAs were still detectable in a sufficient amount to use them as dietary markers. Switching diet experiments demonstrated that FAs typical for a specific diet are already present after one day and are still detectable after 14 days of feeding on a different food source, suggesting that FA analysis can integrate the food choice of Collembola over a longer period of time, in contrast to snapshot methods such as gut content analysis.

Olfactory cues associated with fungal grazing intensity and secondary metabolite pathway modulate Collembola foraging behaviour

Fungal secondary compounds play an important role for springtail food choice and fitness. Little is known, however, on the role of olfactory cues for Collembola foraging behaviour and whether Collembola can olfactorily perceive volatiles associated with fungal secondary metabolite pathways. We investigated the ability of three species of Collembola (Folsomia candida, Heteromurus nitidus and Supraphorura furcifera) to use olfactory cues for discriminating between fungi of different phylogenetic affiliation (Aspergillus nidulans, Cladosporium cladosporioides, Ascomycota; Laccaria bicolor, Basidiomycota) and toxicity using fungal strains of A. nidulans with reduced secondary metabolite production. Furthermore, we studied if olfactory cues from hyphae injured by grazing affect the foraging behaviour of Collembola. We hypothesized that (i) Collembola are able to olfactorily perceive and respond to fungal species/strains with different secondary metabolite pathways and that (ii) Collembola are able to sense fungal mycelia injured by grazing. Each of the Collembola species studied preferentially oriented their foraging towards fungal strains of A. nidulans with suppressed secondary metabolites, and in particular towards the mutant where the global regulator for secondary metabolites (ΔlaeA) has been silenced. Two of the three Collembola species (H. nitidus and S. furcifera) sensed olfactory cues of previously grazed fungi and moved towards ungrazed fungi, however, the response of S. furcifera was restricted to fungi extensively exposed to grazing (5 days) suggesting that the response varies between Collembola species.Overall, the results support the first and second hypothesis indicating that Collembola (1) are able to olfactorily differentiate fungi of different toxicity and move towards more palatable fungi, and (2) showed a lesser preference for fungi previously exposed to grazing.

Fungal toxins affect the fitness and stable isotope fractionation of Collembola

We investigated the effect of the fungal toxin sterigmatocystin on the fitness and stable isotope fractionation of two Collembola species (Folsomia candida and Heteromurus nitidus) feeding on mixed vs. single diets. Four knock out mutants of Aspergillus nidulans with the sterigmatocystin production blocked at different steps along the biosynthetic pathway were combined in mixed diets with either the high quality fungus Cladosporium cladosporioides or the low quality fungus A. nidulans (wildtype). Using fungi labeled with stable isotopes (13C and 15N) we evaluated the incorporation of carbon and nitrogen from individual fungi. We hypothesised that (i) Collembola fitness decreases with the putative toxicity of the fungi (ii) Collembola benefit from ingestion of mixed diets due to toxin dilution and (iii) fractionation of 13C and 15N is more pronounced in more toxic diets. Mixed diets did not uniformly improve fitness. Toxin dilution, however, played an important role in Collembola fitness. The fractionation of 13C and 15N varied with sterigmatocystin mutant strains, and Collembola species often differed from the expected enrichment per trophic level. The results show that fungal toxin production may affect stable isotope fractionation, presumably by altering consumer excretion rates necessary for detoxification.

Habitat structure and prey aggregation determine the functional response in a soil predator–prey interaction

Functional responses describe the per capita consumption rates of predators depending on prey density, which quantifies the energy transfer between trophic levels. We studied a typical interaction of the litter–soil systems between hunting spiders ( Pardosa lugubris ; Araneae: Lycosidae) and springtails ( Heteromurus nitidus ; Collembola: Entomobryidae) at varying habitat structure, i.e. with moss vs. without moss. We found a hyperbolic increase in consumption (functional response type II) in the treatment without habitat structure that was converted into a roller-coaster (or dome-shaped in a broad sense) functional response in treatments with habitat structure. Additional experiments suggest that the reduced per capita consumption rates at high prey densities may be explained by aggregative defence behaviour of the springtails. Experimentally, this behaviour was induced by the presence of habitat structure. We analyzed the net-energy gain of this predator–prey interaction by comparing the predator’s metabolic energy loss to its energy gain by consumption. In treatments with habitat structure, the net-energy gain of the predator was limited at intermediate prey densities where prey aggregation reduced the consumption rates. Our results stress the importance of habitat structure and prey behaviour in shaping the functional response in a typical soil–litter predator–prey interaction.

Taking it to the next level: Trophic transfer of marker fatty acids from basal resource to predators

Fatty acid (FA) analysis is used increasingly to investigate the trophic structure of soil animal food webs as the technique allows separation of the role of detrital resources such as bacteria, fungi and plant material for consumer nutrition. The applicability of FAs as biomarkers for different diets has been verified for Collembola and Nematoda. However, for the analysis of whole food webs it is crucial to know whether marker FA are valid for different taxa and whether they are transferred along the food chain to higher trophic levels, i.e. predators. Top-predators are integrators of lower level energy fluxes in food webs; therefore analysis of their FAs may allow to identify trophic pathways and to separate bacterial vs. fungal based energy channels. Chilopoda and Arachnida are among the main predators in soil food webs. Our aim was to test the applicability of marker FAs for these two predator taxa and to verify the trophic transfer of marker FAs of different basal resources via first order consumers into predators, i.e. over three trophic levels. Therefore, we investigated the transfer of FAs from different basal resources [fungi (Chaetomium globosum), plant leaf litter (Tilia europaea), Gram-positive (Bacillus amyloliquefaciens) and Gram-negative bacteria (Stenotrophomonas maltophilia)] via Collembola (Heteromurus nitidus) as first order consumers into predators [Lithobius forficatus (Chilopoda) and Pardosa lugubris (Arachnida)]. Fatty acid profiles of predators of food chains with different basal resources differed significantly. Marker FAs of basal resources were clearly detectable in predators, suggesting that FA analysis allows to separate trophic channels of soil food webs. By reflecting basal resources, FAs of predators allow tracking energy/resource fluxes through the food web and thereby clarifying the relative importance of bacterial vs. fungal vs. plant resources for soil animal food webs.