A preliminary checklist of the ants (Hymenoptera, Formicidae) of Andorra

Within the last decade, checklists of the ant fauna of several European countries have been published or updated. Nevertheless, no ant checklists have hitherto been published for the principality of Andorra, a small landlocked country located in the eastern part of the Pyrenees. This work presents a critical list of the ant species of Andorra based on a review of the literature and on the biological material we collected during several field campaigns conducted in Andorra since the year 2005. Seventy-five species belonging to 21 genera of were recorded. Nine species were recorded for the first time in Andorra: Aphaenogaster gibbosa (Latreille, 1798), (Olivier, 1792), (Leach, 1825), Nylander, 1846, Seifert, 1992, Forel, 1895, (Bondroit, 1918), (Forel, 1894), (Mayr, 1855). The most speciose genera were Linnaeus, 1758 and Forel, 1890 with 14 and 12 species, respectively. The ant fauna of Andorra is mostly dominated by Central European species (some are typical cold climate specialists); however species belonging to the Mediterranean ant fauna were also found. This can be explained by the particular geographic situation of Andorra which is characterized by a high mountain Mediterranean climate

Individual rules for trail pattern formation in Argentine ants (Linepithema humile)

We studied the formation of trail patterns by Argentine ants exploring an empty arena. Using a novel imaging and analysis technique we estimated pheromone concentrations at all spatial positions in the experimental arena and at different times. Then we derived the response function of individual ants to pheromone concentrations by looking at correlations between concentrations and changes in speed or direction of the ants. Ants were found to turn in response to local pheromone concentrations, while their speed was largely unaffected by these concentrations. Ants did not integrate pheromone concentrations over time, with the concentration of pheromone in a 1 cm radius in front of the ant determining the turning angle. The response to pheromone was found to follow a Weber's Law, such that the difference between quantities of pheromone on the two sides of the ant divided by their sum determines the magnitude of the turning angle. This proportional response is in apparent contradiction with the well-established non-linear choice function used in the literature to model the results of binary bridge experiments in ant colonies (Deneubourg et al. 1990). However, agent based simulations implementing the Weber's Law response function led to the formation of trails and reproduced results reported in the literature. We show analytically that a sigmoidal response, analogous to that in the classical Deneubourg model for collective decision making, can be derived from the individual Weber-type response to pheromone concentrations that we have established in our experiments when directional noise around the preferred direction of movement of the ants is assumed.Comment: final version, 9 figures, submitted to Plos Computational Biology (accepted

Physical and land-cover variables influence ant functional groups and species diversity along elevational gradients

Of particular importance in shaping species assemblages is the spatial heterogeneity of the environment. The aim of our study was to investigate the influence of spatial heterogeneity and environmental complexity on the distribution of ant functional groups and species diversity along altitudinal gradients in a temperate ecosystem (Pyrenees Mountains). During three summers, we sampled 20 sites distributed across two Pyrenean valleys ranging in altitude from 1,009 to 2,339 m by using pitfall traps and hand collection. The environment around each sampling points was characterized by using both physical and land-cover variables. We then used a self-organizing map algorithm (SOM, neural network) to detect and characterize the relationship between the spatial distribution of ant functional groups, species diversity, and the variables measured. The use of SOM allowed us to reduce the apparent complexity of the environment to five clusters that highlighted two main gradients: an altitudinal gradient and a gradient of environmental closure. The composition of ant functional groups and species diversity changed along both of these gradients and was differently affected by environmental variables. The SOM also allowed us to validate the contours of most ant functional groups by highlighting the response of these groups to the environmental and land-cover variables

Foraging activity pattern and herbivory rates of the grass-cutting ant Atta capiguara

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Does substrate coarseness matter for foraging ants? An experiment with Lasius niger (Hymenoptera; Formicidae)

International audienceWe investigated whether workers of the ant species Lasius niger are able to sense and discriminate the coarseness of the substrate on which they walk. First, we studied the way in which substrate coarseness affects the ants' locomotory behaviour. Second, we investigated the spontaneous preference of ants for substrates of different coarseness. And third, we tested with a differential conditioning procedure the ants' capacity to learn to associate a given coarseness with a food reward. The locomotory behaviour of ants differed according to substrate coarseness: ants moved significantly faster and had more sinuous trajectories on a fine than on a coarse substrate. No spontaneous preference for a substrate of a given coarseness was observed and, even after 20 successive conditioning trials, there was little evidence of the effect of experience on substrate coarseness discrimination. Overall however, ants trained on fine sand made significantly more correct choice than those trained on coarse sand. We discuss these results and argue that in L. niger substrate coarseness may be more important at the collective level, by interacting with the chemical properties of the pheromone trail used in mass recruitment to food source, than at the individual level

A preliminary checklist of the ants (Hymenoptera, Formicidae) of Andorra

Within the last decade, checklists of the ant fauna of several European countries have been published or updated. Nevertheless, no ant checklists have hitherto been published for the principality of Andorra, a small landlocked country located in the eastern part of the Pyrenees. This work presents a critical list of the ant species of Andorra based on a review of the literature and on the biological material we collected during several field campaigns conducted in Andorra since the year 2005. Seventy-five species belonging to 21 genera of were recorded. Nine species were recorded for the first time in Andorra: Aphaenogaster gibbosa (Latreille, 1798), (Olivier, 1792), (Leach, 1825), Nylander, 1846, Seifert, 1992, Forel, 1895, (Bondroit, 1918), (Forel, 1894), (Mayr, 1855). The most speciose genera were Linnaeus, 1758 and Forel, 1890 with 14 and 12 species, respectively. The ant fauna of Andorra is mostly dominated by Central European species (some are typical cold climate specialists); however species belonging to the Mediterranean ant fauna were also found. This can be explained by the particular geographic situation of Andorra which is characterized by a high mountain Mediterranean climate

Profils comportementaux et spécialisation fonctionnelle lors de l’exploitation de ressources alimentaires chez la fourmi Lasius niger.

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Differential responses to chemical cues correlate with task performance in ant foragers

International audienceDivision of labor in social insects has been explained by response threshold models which are based on differential responses to task-specific stimuli. In the present study, we argue that other types of stimuli, such as location-related cues, which are correlated with but not directly linked to task performance, may be significant. Using the black garden ant Lasius niger as a model, we focused on three groups of workers that perform extranidal tasks: (1) scouts, which explore new and unmarked areas remote from the nest; (2) patrollers, which are not recruited by other ants, but nonetheless walk outside in the nest vicinity; and (3) recruits, which are temporary foragers whose exit is triggered by recruitment. We used standardized tests to investigate, in a context-independent way, whether differences in task performance by these three groups could be correlated to intrinsic differences in their responsiveness to trail pheromone or to nest-related stimuli such as the presence of nestmates or colony odor. Overall, we found that the task profile of workers was correlated neither with their tendency to explore unmarked areas nor with their social attraction to nestmates. Scouts showed a lower attraction to colony odor and lower scores of trail following than recruits. Conversely, recruits were more attracted to colony chemical cues and showed lower response threshold to trail pheromone. Patrollers displayed behaviors between those of recruits and scouts. Our study thus shows that differences in ant responsiveness to location-related cues and recruitment trails contribute to the regulation of extranidal tasks in ants. Significance statement Work organization in insect societies has been explained by models of differential response thresholds to stimuli that are directly linked to the performance of specific tasks. However, the task performance of individuals could also depend on their responsiveness to social and location-related cues that are correlated but not directly linked to these tasks. Using standardized context-independent tests, we found that scout ants, which explore unknown areas, display a lower responsiveness to colony area marking and trail pheromone. Conversely, recruits, which forage outside the nest only during food exploitation, are the most attracted to nestmates, colony area marking and trail pheromone. Patrollers display intermediate levels of attraction. Location-related cues could therefore play a role in determining the level of task performance by ants and should be taken into consideration in threshold models of task allocation

Locomotor pattern and mechanical exchanges during collective load transport

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