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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Reorientation patterns in central-place foraging: Internal clocks and klinokinesis

Campos D., Bartumeus F., Mendez V., Espadaler X. (2014) Reorientation patterns in central-place foraging: Internal clocks and klinokinesis. Journal of the Royal Society Interface. 11: 0-0.
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Doi: 10.1098/rsif.2013.0859

Resum:

We study central-place foraging patterns of Aphaenogaster senilis ants at a population level by video framing individual ant trajectories in a circular arena with a nest connected to its centre. The ants naturally leave and enter the nest and forage generating non-trivial movement patterns around the nest. Our data analysis indicated that the trajectories observed can be classified into two strategies: the risk-averse strategy, which involves wandering around the nest without departing far from it and the riskprone strategy, which involves long exploration paths with periodic returns to the central region, nearby the nest. We found that both risk-prone and risk-averse strategies exhibit qualitatively the same reorientation patterns, with the time between consecutive reorientations covering a wide range of scales, and fitting a stretched exponential function. Nevertheless, differences in the temporal scales and the time variability of such reorientation events differ, together with other aspects of motion, such as average speed and turns. Our results give experimental evidence that the internal mechanisms driving reorientations in ants tend to favour frequently long relocations, as theory predicts for efficient exploration in patchy landscapes, but ants engaged in central-place foraging can modulate such behaviour to control distances from the nest. Previous works on the species support the idea that risk-prone and risk-averse strategies may reflect actual differences between individuals age and experience; these factors (age and experience) should be then relevant in modulating the internal reorientation clocks. To support the validity of our findings, we develop a random-walk model combining stretched exponential reorientation clocks with klinokinesis that fits the time length and the travelled distance distributions of the observed trajectories. © 2013 The Author(s) Published by the Royal Society. All rights reserved.

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Rickia lenoirii, a new ectoparasitic species, with comments on world Laboulbeniales associated with ants

Santamaria S., Espadaler X. (2014) Rickia lenoirii, a new ectoparasitic species, with comments on world Laboulbeniales associated with ants. Mycoscience. : 0-0.
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Doi: 10.1016/j.myc.2014.06.006

Resum:

A new species of the genus Rickia is described on ants of the genus Messor based on collections from Greece and France. Rickia lenoirii is distinguished from Rickia wasmannii by the smaller size of the thallus and by the fewer number of cells in each of the three series, as well by other characteristics. The newly described species belongs to the perlata morphological group and because of its diminutive thallus may be compared with similar small species, mostly on mites; therefore it could be included among acarophilous forms according to an old Thaxter definition. The database of ant-Laboulbenial interactions consists of 43 species, 10 genera, and three subfamilies of ants documented as hosts for the six Laboulbeniales known from ants worldwide. Some ant Laboulbenial species show a low host phylogenetic specificity while other species are much restricted in their host range. The highly biased known distribution of ant Laboulbeniales is probably an artifact and the database is far from being complete. © 2014 The Mycological Society of Japan.

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