Gone with the wind: short and long-term responses of leaf-cutting ants to the negative effects of wind on their foraging activity

ALMA, MARINA; ALEJANDRO GUSTAVO FARJI BRENER; ELIZALDE, LUCIANA

Ilehus

Congreso; XXII Simposio de mirmecología-International Ant Meeting.; 2015

Since reproduction and survival of organisms depend on their feeding; it seems intuitive that foraging behaviors may be selecting for maximizing benefits and reducing costs. One variable that might affect the foraging of leaf-cutting ants is the wind, which may reduce ants? speed or blow them away the trail when impacts on their loads. Our aims were to evaluate whether (1) the wind affects negatively foraging activity; (2) this effect varies with trails? orientation, vegetation around them and loads? area, mass and shape; and (3) ants adopt short and long-term responses to reduce the wind effect; i.e. whether in windy conditions ants select loads? area, mass and shape which reduce their intercept with wind; and whether in windy regions trails? system have a spatial distribution that reduce the wind effect, respectively. To evaluate this, we worked with Acromyrmex lobicornis, a leaf-cutting ant that inhabits windy and windless regions. We filmed parallel and perpendicular trails with and without vegetation from 19 nests during 2 min 30 s in natural windy and windless conditions (4-9 and 0 km/h, respectively), and measured ants? speed and number of times ants were blown away the trail. Also, we generated artificial wind (4 km/h) with computer coolers in the trails of 13 nests, and captured 10 ants of similar size per nest and their loads; we measured the same variables mentioned before and the loads? area, mass and shape. Finally, to evaluate the short and long-term response, we offered paper fragments with different size, mass and shape in windy and windless conditions, and we measured the cardinal orientation of trails in a windy and windless region. We found that in windy conditions, the load ants reduced their speed 78% and were blown away the trail 39 times more. The wind affected only load ants that were walking in perpendicular or upwind parallel trails without vegetation; and the wind effect increased with loads? area, mass and shape. In the short-term, the ants reduced the wind effect selecting small, light or rectangular loads; even, they were able to solve daily wind variation in this way. However, the trails did not show a spatial distribution that reduced the wind effect. This is the first study that quantifies the negative wind effect on leaf-cutting ants foraging, and brings to light that workers can reduce this effect selecting the loads which reduce the wind intercept. Long-term responses like trail orientation, seem to be molded by other factors. These results not only show the adverse effects on foraging of an ignored environmental factor, but also illustrate how short-term behavioral responses can mitigate these effects.