Predation on epigeic, endogeic and anecic earthworms by carabids active in spring and autumn

Background and purpose:Generalist predatory carabid beetles have an important role in controlling the abundance of various prey species within ecosystems, including certain pests. In terms of bio-control, these unspecialised predators may be sustained in the field when pest populations are low by predating on other animals such as earthworms. The aim of this study was to reveal patterns in predation by beetles, represented by the carabid community in the field, on different earthworm species with respect to anecic, endogeic and epigeic earthworm ecotypes.Materials and methods:We utilised DNA extracted from the gut content of 23 carabid species to reveal predation on earthworms directly in the field, considering spring and autumn aspects. The extracted DNA from each carabid species collected in the field was then screened using PCR with earthworm species-specific primers.Results and discussion:After screening the carabids using five earthworm species-specific primer pairs, 20 species, including 53% of all tested individual beetles, were positive for earthworms, with similar proportions in the spring and autumn samples and between the sexes. Earthworms from all three ecotypes were confirmed within the predator guts and were widely consumed within the carabid community.Conclusions:These results suggest that predation on earthworms might be an important mechanism sustaining populations of generalist predatory carabids in the field, which can be advantageous for biological control. Therefore, non-conventional management should be improved to maintain the three ecotypes of the earthworm community as prey for beneficial predatory carabids.</p

Estimation of trophic niches in myrmecophagous spider predators

Among spiders, taxonomically the most diversified group of terrestrial predators, only a few species are stenophagous and feed on ants. The levels of stenophagy and ant-specialisation vary among such species. To investigate whether stenophagy is only a result of a local specialisation both fundamental and realised trophic niches need to be estimated. Here we investigated trophic niches in three closely-related spider species from the family Gnaphosidae (Callilepis nocturna, C. schuszteri, Nomisia exornata) with different levels of myrmecophagy. Acceptance experiments were used to estimate fundamental trophic niches and molecular methods to estimate realised trophic niches. For the latter two PCR primer sets were used as these can affect the niche breadth estimates. The general invertebrate ZBJ primers were not appropriate for detecting ant DNA as they revealed very few prey types, therefore ant-specific primers were used. The cut-off threshold for erroneous MOTUs was identified as 0.005% of the total number of valid sequences, at individual predator level it was 0.05%. The fundamental trophic niche of Callilepis species included mainly ants, while that of N. exornata included many different prey types. The realised trophic niche in Callilepis species was similar to its fundamental niche but in N. exornata the fundamental niche was wider than realised niche. The results show that Callilepis species are ant-eating (specialised) stenophagous predators, catching mainly Formicinae ants, while N. exornata is an ant-eating euryphagous predator catching mainly Myrmicinae ants

Sex and age-biased nematode prevalence in reptiles

Prevalence and intensity of parasitic infections are often higher in male than in female vertebrates. This bias may represent either differences between host sex in exposure or susceptibility to parasites. The former may be due to sex-specific behaviour of the host, including differential habitat use or diet. Differences in susceptibility are often regarded as a negative effect of male sex steroid hormones on the immune system. Host–parasite dynamics are of great interest in terms of reptile survival, ecology and conservation. We used, for the first time, molecular diagnostics to track nematode parasitism in wild populations of reptiles noninvasively. Using slow worms (Anguis fragilis) as a model species, we investigated the interacting effects of time of year, sex, length, weight and climatic variables on the prevalence of the gastroenterological parasitic nematode Neoxysomatium brevicaudatum. Faeces were collected from three sites over 2 years. There was an interaction between sex and time of year, with lower nematode prevalence in males than in females in July or August (different between years) but a high prevalence in males in April. As the latter is during the slow worm breeding season, this may be the result of testosterone-induced immunosuppression. A second-order interaction between slow worm length and weight was found to be significant, with a positive association between prevalence and body condition in young slow worms and a negative association in older slow worms. The convex pattern of nematode prevalence with age that emerged suggests an increase with age-related exposure and a decrease with age-related acquired immunity

Editorial

This issue of the Bulletin of Entomological Research is a little different, in that it includes eight papers from a conference held last year at the University of Innsbruck, Austria, entitled ‘Molecular approaches to study trophic interactions: current progress and future directions’. Details of the meeting can still be found at www.mti-symposium.at. The meeting was organised to bring together researchers in the growing fields of molecular analysis of predation and parasitism. The aim was to discuss and synthesize the latest progress in these fields, to discuss techniques, to identify promising avenues for future research and to stimulate cooperation and collaboration. A major objective was also to attract those new to, or interested in, using these approaches and to provide a workshop that would help them get started and to understand the advantages and limitations of molecular approaches. The meeting was deliberately cross-discipline, bringing together people working on vertebrates and invertebrates, terrestrial and aquatic systems, but all with a common interest in trophic relationships and their study using molecular approaches. There were over 70 researchers and students from 15 countries at this highly diverse, three-day conference. Four sessions were held and introduced by keynote speakers, each an international leader in his field: Simon Jarman (Australian Antarctic Division, Australia) introduced the session on predation in aquatic systems, and Andrew King (Cardiff University, UK) provided us with an overview on predation in terrestrial systems. The session on the analysis of blood meals was opened by Steven Torr (University of Greenwich, UK), while Matt Greenstone (USDA, USA) provided (remotely) a keynote address on molecular approaches to study endoparasitism. The keynote presentations were followed by an array of highly interesting talks, complemented by posters. This special issue of Bulletin of Entomological Research, therefore, includes papers form this techniques-based meeting that are by no means all entomological. Our justification for this diversion from our usual editorial policies is that the molecular approaches used are widely applicable across taxonomic divisions. Thus, a technique developed to detect dietary components in the guts of krill might be equally useful to someone working on predation by carabid beetles or ladybirds. We make no apologies, therefore, for including papers on the gut microflora of lumbricid earthworms and the diets of rock lobsters alongside more familiar entomological studies on predation and parasitism. These papers clearly demonstrate that molecular analyses are providing us with exciting new ways to study trophic relationships within food webs in a range of aquatic and terrestrial ecosystems. We would like to thank all participants at the Symposium who made this conference such a rewarding and productive meeting, but especially those who have contributed to this special edition. We look forward to regular future symposia in this fast-moving field

Early-season predation on aphids by winter-active spiders in apple orchards revealed by diagnostic PCR

Aphids are major pests in apple orchards, debilitating the crop and spreading disease. We investigated whether early-season predation by canopy spiders may be effectively controlling aphid numbers in three organic orchards. For this purpose, we monitored the aphid population dynamics from the winter eggs to colony stages and compared this to spider abundances and rates of predation on aphids detected by diagnostic polymerase chain reaction. For the latter, we applied existing general aphid primers. We found that spiders ate colony fundatrices and that aphid numbers were negatively related to spider abundance. Spiders were the main active predators within the orchards when the first colony fundatrices were present, indicating their importance in the early control of aphid populations

Molecular evidence for gender differences in the migratory behaviour of a small seabird

Molecular sexing revealed an unexpectedly strong female bias in the sex ratio of pre-breeding European Storm Petrels (Hydrobates pelagicus), attracted to playback of conspecific calls during their northwards migration past SW Europe. This bias was consistent across seven years, ranging from 80.8% to 89.7% female (mean annual sex ratio ± SD = 85.5% female ±4.1%). The sex ratio did not differ significantly from unity (i.e., 50% female) among (i) Storm Petrel chicks at a breeding colony in NW France, (ii) adults found dead on beaches in Southern Portugal, (iii) breeding birds attending nest burrows in the UK, captured by hand, and (iv) adults captured near a breeding colony in the UK using copies of the same sound recordings as used in Southern Europe, indicating that females are not inherently more strongly attracted to playback calls than males. A morphological discriminant function analysis failed to provide a good separation of the sexes, showing the importance of molecular sexing for this species. We found no sex difference in the seasonal or nocturnal timing of migration past Southern Europe, but there was a significant tendency for birds to be caught in sex-specific aggregations. The preponderance of females captured in Southern Europe suggests that the sexes may differ in migration route or in their colony-prospecting behaviour during migration, at sites far away from their natal colonies. Such differences in migration behaviour between males and females are poorly understood but have implications for the vulnerability of seabirds to pollution and environmental change at sea during the non-breeding season

Molecular analysis of the diets of snakes: changes in prey exploitation during development of the rare smooth snake Coronella austriaca

Reptiles are declining in many parts of the world, mainly due to habitat loss and environmental change. A major factor in this is availability of suitable food. For many animals, dietary requirements shift during developmental stages and a habitat will only be suitable for conserving a species if it supports all stages. Conventional methods for establishing diet often rely on visual recognition of morphologically identifiable features of prey in faeces, regurgitation or stomach contents, which suffer from biases and poor resolution of taxa. DNA-based techniques facilitate noninvasive analysis of diet from faeces without these constraints. We tested the hypothesis that diet changes during growth stages of smooth snakes (Coronella austriaca), which have a highly restricted distribution in the UK but are widespread in continental Europe. Small numbers of the sympatric grass snake (Natrix natrix) were analysed for comparison. Faecal samples were collected from snakes and prey DNA analysed using PCR, targeting amphibians, reptiles, mammals and invertebrates. Over 85% of smooth snakes were found to have eaten reptiles and 28% had eaten mammals. Predation on mammals increased with age and was entirely absent among juveniles and subadults. Predation on reptiles did not change ontogenetically. Smooth snakes may, therefore, be restricted to areas of sufficiently high reptile densities to support young snakes

New universal ITS2 primers for high-resolution herbivory analyses using DNA metabarcoding in both tropical and temperate zones

DNA metabarcoding is a rapidly growing technique for obtaining detailed dietary information. Current metabarcoding methods for herbivory, using a single locus, can lack taxonomic resolution for some applications. We present novel primers for the second internal transcribed spacer of nuclear ribosomal DNA (ITS2) designed for dietary studies in Mauritius and the UK, which have the potential to give unrivalled taxonomic coverage and resolution from a short-amplicon barcode. In silico testing used three databases of plant ITS2 sequences from UK and Mauritian floras (native and introduced) totalling 6561 sequences from 1790 species across 174 families. Our primers were well-matched in silico to 88% of species, providing taxonomic resolution of 86.1%, 99.4% and 99.9% at the species, genus and family levels, respectively. In vitro, the primers amplified 99% of Mauritian (n = 169) and 100% of UK (n = 33) species, and co-amplified multiple plant species from degraded faecal DNA from reptiles and birds in two case studies. For the ITS2 region, we advocate taxonomic assignment based on best sequence match instead of a clustering approach. With short amplicons of 187–387 bp, these primers are suitable for metabarcoding plant DNA from faecal samples, across a broad geographic range, whilst delivering unparalleled taxonomic resolution

Silk versus venom: alternative capture strategies employed by closely related myrmecophagous spiders

Predators that prey on dangerous species have evolved effective capture traits. In spiders, venom and silk represent distinct substances associated with prey capture. However, the use of such adaptations comes at a cost. Based on a possible trade-off, the use of only one effective capture mechanism should be optimized if a predator is to specialize on a single type of dangerous prey. We investigated hunting strategies in two Callilepis spp. and one Nomisia species, Nomisia exornata, closely related ant-eating spiders from the family Gnaphosidae. We hypothesized that specialized Callilepis spiders would adopt a more stereotyped capture strategy compared with less specialized Nomisia. We also expected that Callilepis would rely on only one subjugation mechanism. To test this, we compared their hunting efficacy and hunting strategies, with an emphasis on venom vs. silk utilization. Nomisia restrained ants with silk (then bit them), whereas Callilepis relied solely on its venom. This was also reflected in trophic traits connected with silk and venom utilization; Callilepis had larger venom glands than Nomisia, whereas Nomisia had more piriform silk glands than Callilepis. Callilepis was more effective because it subdued prey more quickly, presumably owing to ant-specific venom. Callilepis and Nomisia handled ants from two subfamilies with different degrees of success; Callilepis was more successful with Formicinae ants, whereas Nomisia handled Myrmicinae ants better. We show that sole reliance on venom allows Callilepis to be more efficient in overcoming ants than Nomisia, which uses both silk and venom. However, such specific adaptations might restrict specialized predators from exploiting alternative prey