Two feedback mechanisms involved in the control of leaf fragment size in leaf-cutting ants.

Polymorphic leaf-cutting ants harvest leaf fragments that correlate in size with the workers' body size. When cutting, workers anchor their hind legs on the leaf edge and rotate, removing approximately semicircular fragments. Workers show behavioural plasticity and modify their leg extension while holding onto the leaf edge depending on, for instance, leaf toughness, cutting smaller fragments out of tough leaves.

Symbiont demand guides resource supply: leaf-cutting ants preferentially deliver their harvested fragments to undernourished fungus gardens.

Leaf-cutting ants are highly successful herbivores in the Neotropics. They forage large amounts of fresh plant material to nourish a symbiotic fungus that sustains the colony. It is unknown how workers organize the intra-nest distribution of resources, and whether they respond to increasing demands in some fungus gardens by adjusting the amount of delivered resources accordingly.

Carbon dioxide levels and ventilation in nests: significance and evolution of architectural innovations in leaf-cutting ants.

Leaf-cutting ant colonies largely differ in size, yet all consume O and produce CO in large amounts because of their underground fungus gardens. We have shown that in the genus, three basic nest morphologies occur, and investigated the effects of architectural innovations on nest ventilation. We recognized (i) serial nests, similar to the ancestral type of the sister genus , with chambers excavated along a vertical tunnel connecting to the outside via a single opening, (ii) shallow nests, with one/few chambers extending shallowly with multiple connections to the outside, and (iii) thatched nests, with an above-ground fungus garden covered with plant material.

Selection and spatial arrangement of building materials during the construction of nest turrets by grass-cutting ants.

Ants build complex nest structures by reacting to simple, local stimuli. While underground nests result from the space generated by digging, some leaf- and grass-cutting ants also construct conspicuous aboveground turrets around nest openings. We investigated whether the selection of specific building materials occurs during turret construction in grass-cutting ants, and asked whether single building decisions at the beginning can modify the final turret architecture.

Nest Turrets of Grass-Cutting Ants: Micromorphology Reveals Building Techniques and Construction Dynamics.

grass-cutting ants construct conspicuous chimney-shaped nest turrets made of intermeshed grass fragments. We asked whether turrets are constructed by merely piling up nearby materials around the entrance, or whether ants incorporate different materials as the turret develops. By removing the original nest turrets and following their rebuilding process over three consecutive days, age-dependent changes in wall morphology and inner lining fabrics were characterized.

Waste deposition in leaf-cutting ants is guided by olfactory cues from waste.

Social insects often use olfactory cues from their environment to coordinate colony tasks. We investigated whether leaf-cutting ants use volatiles as cues to guide the deposition of their copious amounts of colony refuse. In the laboratory, we quantified the relocation of a small pile of colony waste by workers of Atta laevigata towards volatiles offered at each side of the pile as a binary choice, consisting of either waste volatiles, fungus volatiles, or no volatiles.

Carbon dioxide sensing in the social context: Leaf-cutting ants prefer elevated CO levels to tend their brood.

Social insects show temperature and humidity preferences inside their nests to successfully rear brood. In underground nests, ants also encounter rising CO concentrations with increasing depth. It is an open question whether they use CO as a cue to decide where to place and tend the brood.

Carbon dioxide sensing in an obligate insect-fungus symbiosis: CO2 preferences of leaf-cutting ants to rear their mutualistic fungus.

Defense against biotic or abiotic stresses is one of the benefits of living in symbiosis. Leaf-cutting ants, which live in an obligate mutualism with a fungus, attenuate thermal and desiccation stress of their partner through behavioral responses, by choosing suitable places for fungus-rearing across the soil profile. The underground environment also presents hypoxic (low oxygen) and hypercapnic (high carbon dioxide) conditions, which can negatively influence the symbiont.

Nest enlargement in leaf-cutting ants: relocated brood and fungus trigger the excavation of new chambers.

During colony growth, leaf-cutting ants enlarge their nests by excavating tunnels and chambers housing their fungus gardens and brood. Workers are expected to excavate new nest chambers at locations across the soil profile that offer suitable environmental conditions for brood and fungus rearing. It is an open question whether new chambers are excavated in advance, or will emerge around brood or fungus initially relocated to a suitable site in a previously-excavated tunnel.

Vascular risk prediction in ischemic stroke patients undergoing in-patient rehabilitation - insights from the investigation of patients with ischemic stroke in neurologic rehabilitation (INSIGHT) registry.

Background: In-patient rehabilitation following ischemic stroke offers a unique opportunity for risk factor and lifestyle modification. Quantification of risk in this setting may help to tailor therapy, increase physician awareness and patient compliance and thus to reduce recurrent vascular events.

Aims: To validate the predictive value of established secondary stroke risk scores.

Candidate polyanionic microbicides inhibit human T-cell lymphotropic virus type 1 receptor interactions, cell-free infection, and cell-cell spread.

The human T-cell lymphotropic virus type 1 (HTLV-1) is the cause of adult T-cell leukemia and inflammatory diseases including HTLV-1-associated myelopathy/tropical spastic paraparesis. HTLV-1 can be transmitted through sexual contact, mother-to-child transmission, and exposure to contaminated blood. Microbicides are agents that interfere with microbial infectivity at mucous membranes, and candidates are under development for use against sexually transmitted viruses such as human immunodeficiency virus type 1.