Molecular markers and a sequence deletion in intron 2 of the putative partial homologue of LEAFY reveal geographical structure to genetic diversity in the acutely threatened legume genus Clianthus

Clianthus is an acutely threatened, bird-pollinated genus endemic to New Zealand, represented in the wild by only one population of C. puniceus and 11 populations of C. maximus, each with very few individuals (typically <10 per population). A limited number of named Clianthus cultivars of indeterminate origin are commonly grown as ornamentals. Genomic DNA from individual Clianthus plants was extracted for genetic diversity analysis using a range of molecular markers, including amplified fragment length polymorphism (AFLP). Data were analysed by the unweighted pair-group method with arithmetic averaging (UPGMA), the generation of Neighbor-Joining trees, and analyses of molecular variance (AMOVA). Genetic distance between wild populations of C. maximus was highly correlated with geographical distance between populations. Sequencing of intron 2 of a putative partial homologue of the floral meristem identity gene LEAFY (CmLFY) revealed a 7 bp deletion that was exhibited homozygously in the more northern populations of C. maximus, and in all individuals tested from the sole population of C. puniceus. This deletion was not exhibited in more southern populations of C. maximus. Further, one geographically intermediate population contained some plants that were heterozygous for the deletion. Parallel analyses of cultivated Clianthus genotypes, more than half of which were also homozygous for the 7 bp deletion, showed that these were not representative of the broad, but threatened, diversity remaining in the wild. It is argued that wild populations of C. maximus are unlikely to have arisen from the escape of plants from cultivation. Conservation effort should focus on the protection and study of the extant plants in these wild populations, rather than on the introduction of disturbance regimes to uncover potential seed banks.     

Genetic diversity and local population structure of fragmented populations of Trillium camschatcense (Trilliaceae)

Trillium camschatcense, a long-lived common woodland herb, has been experiencing intensive habitat fragmentation over the last century in eastern Hokkaido, Japan. We examined the genetic diversity and population genetic structure of 12 fragmented populations with different population sizes using allozyme electrophoresis. The percentage of polymorphic loci and mean number of alleles per locus were positively related to population size, probably due to the stochastic loss of rare alleles (frequency of q<0.1) in small populations. Populations with 350 flowering plants or fewer had lost almost all of their rare alleles. While the heterozygosity and inbreeding coefficient were not related to population size, some small populations showed relatively high inbreeding coefficients. In spite of the low genetic differentiation among overall populations (F_ST=0.130), local population structuring was recognized between the two geographically discontinuous population groups. Within groups, sufficient historical gene flow was inferred, whereas a low dispersal ability of this species and geographical separation could produce apparent differentiation between groups.     

Molecular detection of nematode predation and scavenging in oribatid mites: Laboratory and field experiments

Recent stable isotope analyses indicate that a number of putative detritivorous soil microarthropods is not typical detritivores but rather live as predators or scavengers. Using molecular gut content analyses the present study investigates if nematodes indeed form part of the diet of oribatid mites. First, in a no-choice laboratory feeding experiment two nematode species (Phasmarhabditis hermaphrodita and Steinernema feltiae) were offered to eight species of oribatid mites and one gamasid mite. Second, after feeding for 4 and 48 h on each nematode species the detection time of prey DNA in the oribatid mite species Steganacarus magnus was investigated. Third, in a field experiment nematode prey (P. hermaphrodita and S. feltiae) in the diet of microarthropods was investigated distinguishing between scavenging and predation. In the no-choice laboratory experiment not only the gamasid mite but also several of the studied oribatid mite species consumed nematodes. After feeding on nematodes for 4 h prey DNA was detectable in S. magnus for only 4 h, but after feeding for 48 h prey DNA was detectable for 128 h, indicating that the duration of feeding on prey is an important determinant for prey DNA detection. The field experiment confirmed that oribatid mite species including Liacarus subterraneus, Platynothrus peltifer and S. magnus intensively prey on nematodes. Interestingly, DNA of dead P. hermaphrodita was detectable to a similar degree as that of living individuals indicating that scavenging is of significant importance in decomposer food webs. Results of our study indicate that predation and scavenging on nematodes by “detritivorous” microarthropods in soil food webs need to be reconsidered.     

Studies on the mineral nutrition of grain sorghum. III. Populations of the common two spotted spider mite on grain sorghum grown on various levels of N,P and K

Abstract

A greenhouse experiment showed a positive relationship between N, P and K levels in the nutritional solution and the leaves and spider mite development on grain sorghum. In the absence of N or P only small populations of mites develop and in the absence of K no mites were observed. Levels of 2,10% 11, 0.18% P and 1,20% K in the leaves were the minimal values to allow large spider mite populations do develop.     

Do oribatid mites live in enemy-free space? Evidence from feeding experiments with the predatory mite Pergamasus septentrionalis

To examine whether their strongly hardened cuticle permits adult oribatid mites (Acari) to live in enemy-free space, we investigated (1) if Pergamasus septentrionalis, a widespread and abundant predatory mesostigmate mite species, is able to feed on oribatid mites, (2) if this predator preferentially feeds on certain oribatid mite species and (3) to what extent oribatid mites are consumed compared to collembolans and juvenile Mesostigmata. Single adult individuals of six different oribatid mite species (Steganacarus magnus; Nothrus silvestris; Damaeus riparius; Liacarus coracinus; Eupelops plicatus; Achipteria coleoptrata), one collembolan species (Folsomia quadrioculata) and juvenile Pergamasus spp. were offered separately to adult P. septentrionalis in a no-choice feeding experiment. The predators quickly and preferentially fed on collembolans and juvenile Pergamasus; three oribatid mite species were occasionally eaten (L. coracinus, N. silvestris, A. coleoptrata); the other oribatid mite species were rejected as food (E. plicatus, S. magnus, H. riparius). When preying on oribatid mites, P. septentrionalis typically first cut off the legs of the mite, then opened the body through the region of the genital plates or the mouthparts. The results suggest that predator pressure on adult oribatid mites in the field is low, since few relevant predators at the study site are more abundant and powerful than P. septentrionalis. Adult oribatid mites therefore likely indeed live in enemy-free space, i.e. are little affected by predators, but that may not apply to soft-bodied immatures. Collembolans were quickly consumed indicating that they comprise a major part of the diet of P. septentrionalis. Strong feeding on juveniles of Pergamasus suggests that P. septentrionalis also functions as an intra-guild predator.     

Attraction to prey and prey-associated odours by the predatory mite Hypoaspis aculeifer in a soil experimental system

In terms of food searching and trophic interactions among soil organisms volatile signalling plays a crucial role. Still, volatile-based foraging decisions are poorly understood, especially as the dispersal and perception of cues is more restricted within the soil pore space than in simple laboratory approaches where volatiles disperse freely in the air. Focusing on the tritrophic interaction between the soil fungus Trichoderma viride, the fungivorous collembolan Folsomia candida and the predatory mite Hypoaspis aculeifer, we tested the effect of prey and prey-associated volatile signals on the food choice decision of the predatory mite in a laboratory experiment under soil conditions as well as the possible occurrence and relevance of grazing-induced indirect defence signals. The mites showed a clear preference for ungrazed and grazed fungal mycelium. However, we found no evidence of induced indirect defence as ungrazed mycelium was preferred to grazed fungus.     

Detecting hybridization in wild (Coturnix c. coturnix) and domesticated (Coturnix c. japonica) quail populations

Two subspecies of Coturnix coturnix have allopatric distributions in Europe, Maghreb and western Asia (the Common quail C. c. coturnix), and in eastern Asia (the Japanese quail C. c. japonica), except for sympatric breeding areas in the Baikal (Russia) and Kentei (Mongolia) regions, where they could hybridize. Japanese quails have been reproduced in captivity for centuries and domesticated. Massive releasing of Japanese domesticated quails, or hybrids, in west European countries might threaten with hybridization the gene pool of wild quail populations. Here, we used mitochondrial (mtDNA) and nuclear DNA markers (microsatellites), and Bayesian admixture analyses aiming to assess subspecies distinction and identify hybrids in wild and captive-reared quails. A phylogenetic tree identified two major mtDNA clades, corresponding to the two subspecies, and allowed detecting 12 hybrids in wild Common quails sampled in Spain. Additional hybrids were identified in wild quails sampled in Spain, Italy and Senegal using microsatellite markers. Wild quails sampled in Mongolia showed japonica mtDNAs, but their microsatellite genotypes were admixed, suggesting that Common and Japanese quails can hybridize in nature. Some captive-reared stocks of Japanese quails were also admixed. Introgression of domesticated Japanese quail genes in wild Common quail populations might affect the phenotypic expression of functional traits, as body size, feather colours, sexual calls and migratory behaviours. Hence, restocking with captive-reared non-native quails should be banned.     

Analysis of the genetic structure of red-legged partridge (Alectoris rufa, Galliformes) populations by means of mitochondrial DNA and RAPD markers: a study from central Italy

The strong hunting pressure on the red-legged partridge, Alectoris rufa, warranted its inclusion into the list of species of European conservation concern. During the last decades, restocking plans with farmed specimens have counterbalanced the hunting drawings from wild populations. Our concern was the study of A. rufa in the easternmost part of its range, the central Italy, to gain insights into the effects of this compensation practice on the genetic structure of its populations. Partridges from both a geographically isolated, long-time protected, wild population (Pianosa island, Tuscan Archipelago National Park) and two Tuscan farms (Bieri and Scarlino) were investigated. All the specimens were very similar in outward appearance, looking much like to A. rufa. Ninety-six sequences of both Cytochrome b and D-loop Control Region of mitochondrial DNA (mtDNA) were analysed to get evidence of ancestry at the population level, whereas, the Random Amplified Polymorphic DNA (RAPD) technique was employed to get fingerprinting at the individual level. Pianosa and Bieri populations showed both the A. rufa and Alectoris chukar mtDNA lineages, whereas the Scarlino one only the A. rufa-mtDNA line. However, a spread overall pattern of A. rufa × A. chukar hybridisation among specimens, whatever their mtDNA lineage could result to be, was disclosed by means of RAPD species-specific markers. This is the first genetically documented record of the A. rufa × A. chukar hybrids. The occurrence of the pure, native A. rufa genome in the easternmost part of the species’ geographical range may be guessed to be virtual.     

MtDNA genetic diversity and population history of a dwindling raptorial bird, the red kite (Milvus milvus)

The red kite (Milvus milvus) occurs in a relatively small area in the southwestern Palearctic region, with population strongholds in Central Europe. Following strong human persecutions at the beginning of the 20th century, populations have receded, particularly in peripheral areas and islands. In order to describe and compare levels of genetic diversity and phylogeographic patterns throughout its entire distribution in Europe, sequence variation of a 357 bps part of the mitochondrial DNA control region was assessed in eight populations and 105 individuals. Overall, results indicate that population declines have affected red kite mtDNA variation. We found low levels of genetic diversity (values of nucleotide diversity ranging from 0 in Majorca island to 0.0062 in Central Europe), with only 10 distinct haplotypes, separated by low levels of genetic divergence (mean sequence divergence = 0.75%). Highest haplotype and nucleotide diversities match with demographic expectations, and were found in Central European and Central Spanish samples, where present strongholds occur, and lowest values in the declining southern Spanish and insular samples. Φst estimates indicated moderate gene flow between populations. Phylogeographic patterns and mismatch distributions analyses suggest central European regions may have been colonized from southern glacial refugia (in the Italian or Iberian peninsulas). Interspecific phylogenetic comparisons and divergence date estimates indicated the genetic split between the red kite and its closely related species, the black kite (Milvus migrans), might be relatively recent. The low level of genetic variation found in the red kite mitochondrial control region, compared to the black kite, is likely the result of relatively recent divergence (associated with founder events), successive bottlenecks and small population sizes. As there are several ongoing projects aimed at reinforcing populations in countries such as the United Kingdom, Italy or Spain, our results may prove useful for the genetic management of the species.     

Astigmatid mite growth and fungi preference (Acari: Acaridida): Comparisons in laboratory experiments

The relationship between palatability and suitability of fungi for sustaining mite population growth was tested in the laboratory. The effect of mite fungal preference on spore dispersion was also studied. Eight species of microscopic fungi, Alternaria alternata, Aspergillus niger, Aspergillus versicolor, Cladosporium cladosporioides, Eurotium amstelodami var. amstelodami, E. amstelodami var. montevidensis, Mycocladus corymbifer, and Penicillium aurantiogriseum differed in their attractiveness as food and in their suitability to sustain population growth of three astigmatid mites, Acarus siro, Lepidoglyphus destructor and Tyrophagus putrescentiae. The preference for a particular species of fungus and its suitability for sustaining population growth were not correlated. Observed differences among mite species in their population growth were more likely associated with their ability to digest fungi. Fungi were divided into four groups based on their palatability and suitability to sustain population growth: (i) preferred food and suitable for mite growth (e.g. A. alternata, C. cladosporioides); (ii) preferred, but unsuitable (e.g. E. amstelodami var. amstelodami); (iii) avoided, but suitable (e.g. A. versicolor, M. corymbifer and E. amstelodami var. montevidensis); and (iv) avoided and unsuitable (e.g. A. niger). With respect to fungal spore dispersion, mites had the least effect on “avoided and unsuitable” fungal species while preferred fungi were most influenced by mite grazing.     

The specific responses of Acari community to Bt cotton cultivation in agricultural soils in northern China

Transgenic cotton expressing the Bacillus thuringiensis (Bt) insecticidal crystal (Cry1A) protein effectively controls the cotton bollworm and thus has been planted extensively in China. However, the large-scale release of Bt cotton may have undesirable effects on soil fauna due to Bt protein accumulation and the pleiotropic effects of genetic manipulation. A survey of soil mites was carried out monthly for two consecutive years (2009–2010) in Bt and non-Bt cotton fields. The soil mites were extracted using modified Tullgren funnels and were identified to the genus level, when possible. The results suggested that the effects of Bt cotton on soil mite community size were time dependent and taxonomic group specific. The cumulated abundance over a year was always higher in non-Bt fields for Oribatida; this effect was statistically significant in 2010 for Prostigmata and Astigmata. The changes in the community variables tested were similar between Bt and non-Bt cotton fields in 2009, whereas the taxonomic group richness, Shannon–Weaver index and evenness index were significantly different between Bt and non-Bt cotton fields in 2010. Additionally, sharp inter-annual fluctuations in the community composition of the soil mites were found, accompanied with the replacement of some taxonomic groups. Finally, the dominances of some taxonomic groups were significantly different between Bt and non-Bt cotton fields. Bt cotton cultivation fostered Laelapidae populations while inhibited Tectocepheus abundance in 2009. However, Bt cotton cultivation negatively impacted the abundances of Scheloribates and Nothrus in 2010. In conclusion, Bt cotton cultivation exerted specific impacts on soil mites.     

Diversity of soil mite communities when managing plant communities on set-aside arable land

When restoring former agricultural land to more low-nutrient input ecosystems, the establishment of a plant community can be enhanced by sowing desirable species. In this study our aim was to determine whether management of the plant community influences the microarthropod community. We carried out a field experiment in three European countries on set-aside arable land and determined soil mites from the sites in Sweden, The Netherlands and Spain. Experimental plots on set-aside arable land were sown with high (15 species) or low (4 species) plant species seed mixtures; other plots were colonized naturally. A field with continued agricultural practices and a later successional site (target site) were used for comparison with the experimental plots. Soil from the later successional site was inoculated into half of the plots. Abandoning agricultural practices increased the density of mites at one site while the number of mite species was not affected. Sowing plant seeds had no effect on mite densities at any of the sites. The community composition of mites changed in response to management of the plant community, as shown by canonical correspondence analysis. Among the functional groups of mites, saprophytes generally dominated on all plots at all sites. Mites parasitic on insects were not present on fields with continued agricultural practice in Sweden and The Netherlands, and might thus be regarded as an indicator of an increase in trophic complexity in the sown and naturally colonized treatments. Predatory and plant parasitic mites showed no consistent pattern in relation to the treatments of the three sites. Soil inoculation treatment had only a minor impact on the soil mite communities.     

Soil and foliage arthropod communities in conventional,reduced and no-tillage corn (maize,Zea mays L.) systems: A comparison after 20 years of continuous cropping

The influence of long-term (20 years) tillage - moldboard-plowed, reduced- and no-tillage practices - on soil-inhabiting and canopy arthropod communities was examined in corn (maize) systems during a 3-year period. Effects of a soil-applied insecticide (terbufos) on the anrthropod communities were also investigated. Damage by 3 major insect pest species of maize were evaluated: black cutworm, Agrotis ipsilon (Lepidoptera: Noctuidae); European corn borer, Ostrinia nubilalis (Lepidoptera: Pyralidae); corn rootworm beetles, Diabrotica spp. (Coleoptera: Chrysomelidae). Cutworm damage to corn was lowest in the conventional-tillage treatment. Damage by this species was greater in soil-applied insecticide treatments versus no-insecticide treatment. Neither tillage treatment nor insecticide usage had a significant impact on European corn borer damage to corn. Rootworm feeding on corn varied from year to year, with no discernible effect of tillage treatment on damage levels. Total numbers of microarthropods (mites and collembola) were lowest in the conventionally- (moldboard-) plowed treatments and highest in no-tillage treatments. Insecticide treatment significantly increased oribatid mite density, but consistently lowered (although not significantly so) mesostigmatid mite populations. Insecticide application had little if any noticable influence on collembolan (springtail) numbers. With macroarthropod populations, there was a trend toward greater numbers of ground beetles and spiders in the no-tillage systems. Corn rootworm and ladybird beetles (Coccinellidae) accounted for over 95% of the arthropods collected from the corn foliage. With the exception of 2 sampling dates, western corn rootworm beetle density was greater in no-tillage compared with reduced- and conventional-tillage treatments. Ladybird beetle populations were not affected by tillage or insecticide treatments.     

Two genetically distinct units of the Chinese sika deer (cervus nippon): analyses of mitochondrial DNA variation

Chinese sika deer, Cervus nippon, are currently threatened by habitat loss, fragmentation and human hunting, which has led to the extinction of three subspecies in the wild. The remaining subspecies subsist in the narrow regions of Jilin, Heilongjiang, Sichuan, Gansu, Jiangxi, Anhui, and Zhejiang provinces. In order to design effective conservation strategies for the Chinese sika deer, we have investigated genetic diversity, population structure and gene flow in the Chinese sika deer populations by analyzing ≈995 base pairs of the mitochondrial DNA (mtDNA) control region in 59 individuals sampled from the northeast of China, Sichuan, Jiangxi and Zhejiang. Chinese sika deer exhibited low mtDNA diversity and high gene flow among the four populations, and showed no strong geographical structure. The analyses of mtDNA variation among individuals of sika deer identified only two main phylogenetic groups even though three subspecies were sampled. These data singles out the Zhejiang population as being highly genetically distinct and worthy of separate conservation consideration. Therefore, it is recommended that a breeding program for the Zhejiang population be established.     

Tree identity surpasses tree diversity in affecting the community structure of oribatid mites (Oribatida) of deciduous temperate forests

The role of tree diversity and identity as determinants of soil animal community structure is little understood. In a mature deciduous forest dominated by beech we identified clusters of one, two and three tree species of beech, ash and lime allowing to investigate the role of tree species diversity and identity on the density and community structure of oribatid mites. To relate oribatid mite community structure to environmental factors we measured leaf litter input, fine root biomass, mass of organic layers, topsoil pH and C and N content. We expected oribatid mite density to increase with increasing tree diversity, but we expected the effects of tree species identity to override effects of tree diversity. Further, we hypothesized the density of oribatid mites to be reduced by the presence of beech but increased by the presence of lime and ash. As expected tree diversity little affected oribatid mite communities, whereas tree species identity strongly altered density and community structure of oribatid mites. However, in contrast to our expectations the density of oribatid mites was highest in presence of beech indicating that many oribatid mite species benefit from the presence of recalcitrant litter forming thick organic layers. Especially Oppioidea benefited from the presence of beech presumably due to an increased availability of food resources such as fungi and nematodes. Lower density of oribatid mites in monospecific clusters of lime and ash suggests that oribatid mites did not benefit from high quality litter of these species. Notably, large and strongly sclerotized oribatid mite species, such as Steganacarus magnus and Chamobates voigtsi, benefited from the presence of ash and lime. Presumably, these large species better resist harsh microclimatic conditions in shallow organic layers.     

Laboratory studies on pteridophyte breakdown by a soil mite

Twenty six species of pteridophytes (ferns and fern allies) were offered to the soil mite Rhizoglyphus robini Claparède (Acari: Astigmata: Acaridae) in Petri dishes. All plants provided nutrients and promoted growth of mite populations. Leaves of sixteen (61.5%) species were totally consumed or skeletonized while green, another seven only upon browning. The remaining three were left intact even after 3 months, although sori and their leachates provided food for the mites. Paper impregnated with pteridophyte leachates was consumed and encouraged mite reproduction. These findings neither support nor oppose the view that pteridophytes are under-utilized by arthropods but the adaptability of the specific experimental organism might have affected the results. Invertebrates feeding on dead, decomposing pteridophytes possibly reduce the latters' allelopathy to other plants. The ability of Rhizoglyphus to subsist on plant leachates, as well as bacteria or fungi developing thereon, could explain the mode of survival of this and other soil arthropods in deep, mineral soil strata.     

An exploration of wild <Emphasis Type="Italic">Brassica oleracea</Emphasis> L. germplasm in Northern Spain

An intense exploration of the Spanish Cantabrian coast for the presence or absence of wild Brassica oleracea L., yielded 24 new localities to be added to the 21 previously known. Of the resulting 45 localities, 22 correspond to Asturias, 11 to Cantabria and 12 to the Basque Country. Data on the habitat requirements of this plant have been annotated, the conservation status of each population has been estimated and seed samples have been collected for long-term preservation. As a whole, wild B. oleracea is not threatened in Northern Spain, but some populations and/or sub-populations are at risk either because of their small size or some detectable human impact.     

AFLP fingerprinting of Anchusa (Boraginaceae) in the Corso-Sardinian system: Genetic diversity, population differentiation and conservation priorities in an insular endemic group threatened with extinction

Although several plants endemic to Corsica and Sardinia are included in various redlists, no attempts have been made to analyse their genetic diversity with molecular techniques. Genus Anchusa occurs with seven taxa in either mountain or coastal habitats of the two islands, but the very restricted range and low population size pose these endemisms in a very precarious conservation status. Highly variable markers (AFLP) were therefore used to analyse the patterns and levels of genetic diversity in a sample of 11 populations from the entire range of the group.Results indicate the separation between a mountain genic pool including Anchusa formosa, Anchusa capellii and Anchusa montelinasana, and four groups of coastal accessions. In spite of small size, mountain taxa show low interpopulation differentiation (F_st = 0.02) and relatively high intrapopulation genetic variation (0.365), while coastal accessions showed on average a stronger differentiation (mean F_st = 0.20) and a lower diversity (0.281), possibly due to higher rates of inbreeding. The particularly low levels of variation found in A. sardoa, A. littorea and A. crispa ssp. maritima from the Coghinas bay are likely due to a historical decrease of populations and to bottleneck events caused by loss of habitat and natural stochastic factors on sand dune ecosystems. While habitat maintenance and regulation of grazing by domestic herbivores should be sufficient to ensure the persistence of the mountain endemics, additional actions of in situ and ex situ conservation are needed for the critically endangered coastal species A. sardoa and A. littorea. A. crispa showed a relatively high variation, especially on Corsica. No correlation between population size and genetic variation was found in the latter species, highlighting the importance of the small patches for its conservation. Also, the genetic separation between subspecies crispa and maritima stresses the need of keeping them distinct in redlists and conservation actions on Sardinia.     

Epigeic earthworms increase soil arthropod populations during first steps of decomposition of organic matter

Earthworms and soil arthropods are major groups involved in soil decomposition processes. Although the interaction between these organisms can influence decomposition rates, little is known about their population dynamics during the decomposition of organic matter. In this study, we used the pig manure decomposition process to evaluate the effects of the presence of the epigeic earthworm Eisenia fetida on seven groups of soil arthropods: springtails, astigmatid, prostigmatid, mesostigmatid and oribatid mites, psocids and spiders. We carried out an experiment in which low and high doses (1.5 and 3 kg, respectively) of pig manure were applied in consecutive layers to small-scale mesocosms with and without earthworms. The presence of E. fetida increased the overall number of soil arthropods regardless of the dose of manure applied. This result was mainly due to the presence of large populations of springtails and mesostigmatid mites. Springtails were more abundant in the new layers of the mesocosms, which indicated a preference for substrates with fresh organic matter and higher microbial biomass. The other arthropod groups were consistently favored by the presence of earthworms, but remained at low densities throughout the decomposition process. Only the psocids were negatively affected by the presence of E. fetida. These results suggest that the development of large populations of soil arthropods, mainly springtails, in the mesocosms with earthworms is a characteristic feature of the initial stages of the earthworm-driven decomposition process.     

Trophic structure of oribatid mite communities from six different oak forests (Quercus robur)

The degree of trophic plasticity in soil animals is intensely debated. We used stable isotope ratios (¹⁵N/¹⁴N, ¹³C/¹²C) of oribatid mite species from six oak (Quercus robur) forests to investigate (1) if trophic niches vary between forests and (2) the range of trophic levels spanned by oribatid mites. Using litter as baseline stable isotope signatures of most oribatid mite species differed between forests. Therefore, the stable isotope signatures were re-calibrated using stable isotope values of Platynothrus peltifer as primary decomposer species occurring in each of the six forests. Re-calibrated values of nine species (Cerachipteria jugata, Damaeus clavipes, Neotrichoppia variabilis, Oppia denticulata, Hermaniella dolosa, Steganacarus magnus, Ceratozetes peritus, Nanhermannia nana, Xenillus tegeocranus, Eremaeus cordiformis) differed significantly between forests indicating trophic plasticity in most of the studied oribatid mite species. Overall, calibrated stable isotope ratios spanned over 8.7 δ units for ¹⁵N and 5.9 δ units for ¹³C indicating that in forest ecosystems oribatid mite species span about three trophic levels.