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International audience; Ants are well-known for their amazing load carriage performances. Yet, the biomechanics of locomotion during load transport in these insects has so far been poorly investigated. Here, we present a study of the biomechanics of unloaded and loaded locomotion in the polymorphic seedharvesting ant Messor barbarus (Linnaeus, 1767). This species is characterized by a strong intracolonial size polymorphism with allometric relationships between the different body parts of the workers. In particular, big ants have much larger heads relative to their size than small ants. Their center of mass is thus shifted forward and even more so when they are carrying a load in their mandibles. We investigated the dynamics of the ant center of mass during unloaded and loaded locomotion. We found that during both unloaded and loaded locomotion, the kinetic energy and gravitational potential energy of the ant center of mass are in phase, which is in agreement with what has been described by other authors as a grounded-running gait. During unloaded locomotion, small and big ants do not display the same posture. However, they expend the same amount of mechanical energy to raise and accelerate their center of mass per unit of distance and per unit of body mass. While carrying a load, compared to the unloaded situation, ants seem to modify their locomotion gradually with increasing load mass. Therefore, loaded and unloaded locomotion do not involve discrete types of gait. Moreover, small ants carrying small loads expend less mechanical energy per unit of distance and per unit of body mass and their locomotion thus seems more mechanically efficient.

This database gives the vertical height of grass plants lying on the edges of foraging trails of the leaf-cutting ant Atta capiguara at four different times along a period of 13 days. The height of the plants was measured in 5x20cm plots that were submitted to three different treatments. In the control treatment the plots were centered on foraging trails and ants were allowed to cross the plots. In the experimental treatment the plots were also centered on foraging trails but the passage of ants was blocked. Finally, in the simulation treatment the plots were located outside the physical trails and the grass was cut to the ground by experimenters. The experiment was run on three different nests of A. capiguara located in the same pasture near the city of Botucatu, São Paulo state, Brazil. For each nest the three treatments were applied to two different foraging trails. The whole experiment was repeated three times.

International audience; Objective: Gait rehabilitation is a major concern for adults with an intellectual disability or a neu-ropsychological disorder. This study evaluated a collective task exercise that could complement an individual rehabilitation routine in such individuals. The movements of 3 individuals (2 patients and 1 healthy individual) were measured while walking alone and in pairs. The recovery rate, amplitude and speed of centre of mass of individuals walking alone were measured and compared with the values of the centre of mass of the system formed by pairs of individuals. Results: When individuals were walking alone, all parameter values were lower in the 2 patients than in the healthy individual. When the patients were walking in pairs, their recovery rate decreased, but their speed increased when each of them was pai-red with a healthy individual. In pairs, the recovery rate and the amplitude of the centre of mass remained the same as when walking alone. Conclusion: Gait rehabilitation does not appear to improve when intellectually disabled patients walk in pairs compared with when they walk alone. However , walking with a healthy individual seems to be more efficient. litation doctor, a physiotherapist and an occupational therapist re-educate patients. The rehabilitation of gait and motor abilities is an essential part of the treatment, and the patient's walking ability thus needs to be assessed regularly. The main objective of this study was to propose a relevant exercise for this assessment. Based on a protocol used to investigate the collaboration between 2 healthy individuals (1), an exercise was conceived that aimed to enable 2 patients with intellectual disability to work together. The centre of mass (CoM) was measured during a complete walking cycle at constant speed, first of 2 patients walking alone, then of 2 of the same patients walking in pairs together, or with a healthy subject, while linked by an object they were carrying. It was investigated whether, when walking alone, the patients walk in the same way as healthy individuals and whether, when walking in LAY ABSTRACT A standard method to study locomotion is to analyze the trajectory of the center of mass of walking individuals. In our paper we propose to use this method to evaluate the changes in gait efficiency when such patients are walking alone and when they are walking in pairs linked by a load they transport. We worked with two patients suffering from an intellectual disability. These two patients could be paired either together or with their physiotherapist. Our results show that when the patients were walking in pairs their gait was less efficient than when walking alone. However, when the patients were paired with their physiotherapist, gait efficiency was the same as that as when they were walking alone. We suggest that this collective work could be used as a physical, social and mental exercise they could perform with their physiotherapist and that could be included in their rehabilitation routine.

Camponotus renggeri and C. rufipes are very abundant in Brazilian cerrado savannah, where they feed extensively on liquid rewards and commonly associate with plants bearing extrafloral nectaries and honeydew-producing insects. Here, we provide a qualitative and quantitative field account on the natural history and ecology of these two ant species. The study was carried out in a cerrado reserve in south-eastern Brazil across a rainy/hot season (summer) and a dry/cold season (winter). The ants were found in two vegetation physiognomies: all nests of C. rufipes were located in the cerrado sensu stricto (scrub of shrubs and trees, 3–8 m tall), whereas C. renggeri occurred mostly in the cerradão (forest with more or less merging canopy, 10–12 m tall). Both species nested in fallen or erect dead trunks, as well as underground. In addition, C. rufipes built nests using dead plant material arranged or not around shrub bases. Colonies of C. rufipes were generally more populous than those of C. renggeri, and both species had colonies with more than one dealated queen. Both species were active mainly at night and foraged for resources near their nests, mainly extrafloral nectar and hemipteran honeydew (aphids and mealybugs). The average size of the home ranges of C. renggeri in cerrado sensu stricto and cerradão varied from ≈ 2.8 to 4.0 m2 and apparently were not affected by season. In C. rufipes, however, foraging grounds in cerrado sensu stricto showed a twofold increase from dry/cold (≈ 4.5 m2) to rainy/hot season (≈ 9.8 m2). Our study highlights the importance of natural history data to understand the foraging ecology and role of these ants in cerrado savannah.

International audience; We studied in the field the load transport behavior of workers of the polymorphic Mediterranean seed harvester ant Messor barbarus. Individual ants used two different methods to transport food items: carrying and dragging. The probability of dragging instead of carrying varied significantly with both the mass of the item transported and its linear dimension. Moreover, the values of item mass and length at which dragging began to occur increased with increasing size of the workers. However, larger ants began dragging at decreasing values of the relative mass represented by the items transported, which reflects different biomechanical constraints resulting from allometric relationships between the different parts of their body. Transport rate was significantly higher in large ants but varied in the same way for workers of different sizes with the relative mass of the item transported. Nevertheless, although large ants were individually more efficient than small ants in transporting food items, the relative transport rate, defined as the ratio of transport rate to the mass of the ant, was higher for small ants than for large ants. Colonies should thus have a greater benefit in investing in small ants than in large ants for the transport of food items. This may explain why the proportion of large ants is so small on the foraging columns of M. barbarus and why large ants are most often employed in colonies for tasks other than transporting food items.