Evaluating the importance of trophobiosis in a Mediterranean ant community: a stable isotope analysis

Brewitt K., Pinol J., Werner C., Beyschlag W., Espadaler X., Perez Hidalgo N., Platner C. (2014) Evaluating the importance of trophobiosis in a Mediterranean ant community: a stable isotope analysis. Insectes Sociaux. : 0-0.
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Doi: 10.1007/s00040-014-0375-1

Resum:

Trophobiosis between aphids (Aphididae, Hemiptera) and ants (Formicidae, Hymenoptera) is considered to provide an important source of nutrition for ants by aphid honeydew and aphids themselves used as prey. However, little is known about nutrient fluxes and the relative importance of trophobiosis for different ant species. Combining direct contact observations between ants and aphids with stable isotope analyses of distinct multitrophic sample sets (soil, plant, aphid, and ant), we aimed at disentangling the importance of trophobiosis in a Mediterranean food web and possible feedbacks on the functional diversity of ants in a species-rich organic Citrus plantation. We analyzed δ13C- and δ15N-values of sample sets for fertilized and natural soil, using the fertilizer as natural isotope label. The results showed trophic relationships between 18 host plant species, 22 aphid species, and 7 ant species. Direct observation revealed at least 40 different plant–aphid combinations and 25 aphid–ant combinations with a marked range of δ15N-values. However, the δ13C and δ15N isotope ratios still reflected the trophic levels. A significant correlation occurred between the isotope ratios of aphids and their host plants. However, no relationship was found between aphids and ants or between plants and ants revealing that many ant species do not exhibit a close relationship with their trophobiotic partners. Isotopic data allowed us to separate ant species into trophic functional groups and showed the relevance of other food resources. The applied fertilizer shifted the isotopic baseline for the whole trophic system. By combining the stable isotope analysis with the exact origin of the samples, we avoided a misleading interpretation of the high isotopic range of species. Thus, we emphasize the importance of considering a baseline in stable isotope food web studies.

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A pragmatic approach to the analysis of diets of generalist predators: The use of next-generation sequencing with no blocking probes

Pinol J., San Andres V., Clare E.L., Mir G., Symondson W.O.C. (2014) A pragmatic approach to the analysis of diets of generalist predators: The use of next-generation sequencing with no blocking probes. Molecular Ecology Resources. 14: 18-26.
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Doi: 10.1111/1755-0998.12156

Resum:

Predicting whether a predator is capable of affecting the dynamics of a prey species in the field implies the analysis of the complete diet of the predator, not simply rates of predation on a target taxon. Here, we employed the Ion Torrent next-generation sequencing technology to investigate the diet of a generalist arthropod predator. A complete dietary analysis requires the use of general primers, but these will also amplify the predator unless suppressed using a blocking probe. However, blocking probes can potentially block other species, particularly if they are phylogenetically close. Here, we aimed to demonstrate that enough prey sequence could be obtained without blocking probes. In communities with many predators, this approach obviates the need to design and test numerous blocking primers, thus making analysis of complex community food webs a viable proposition. We applied this approach to the analysis of predation by the linyphiid spider Oedothorax fuscus in an arable field. We obtained over two million raw reads. After discarding the low-quality and predator reads, the libraries still contained over 61 000 prey reads (3% of the raw reads; 6% of reads passing quality control). The libraries were rich in Collembola, Lepidoptera, Diptera and Nematoda. They also contained sequences derived from several spider species and from horticultural pests (aphids). Oedothorax fuscus is common in UK cereal fields, and the results showed that it is exploiting a wide range of prey. Next-generation sequencing using general primers but without blocking probes provided ample sequences for analysis of the prey range of this spider and proved to be a simple and inexpensive approach. © 2013 John Wiley & Sons Ltd.

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