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Collective responses of leaf-cutting ants to the negative effect of wind on their foraging activity
ALMA MARINA A; FARJI-BRENER, ALEJANDRO G; ELIZALDE LUCIANA
Simposio; XXII Simpósio de Mirmecologia; 2015
Social organisms deal with everyday problems that can solve through individual or collective responses. In Patagonia, the constant and strong winds reduce foraging rate of leaf-cutting ants, delaying workers? speed and movement. Also, in leaf-cutting ants whole body adhesion and contact area per leg increase with body size. Therefore, one collective response to mitigate the negative wind effect may be assigning larger forager ants in windy conditions. We tested whether (1) the wind effect on ants? speed and movement decreases with increasing ant size; and (2) larger ants are assigned to foraging in windy conditions. We worked with Acromyrmex lobicornis, a leaf-cutting ant that inhabits windy regions of Patagonia. On the one hand, we generated artificial wind and measured ant speed, number of times that ants were blown off the trail, and the time spent by ants for getting used to a wind condition (hereafter, transition time). We obtained these measurements for large (5-7 mm) and small ants (2-4 mm), and before and after the wind treatment. On the other hand, to test whether colonies assign larger foragers in windy conditions, we measured the ants? size in 10 nests in natural windy and windless conditions. We found that the effect of wind was lower on large than on small ants. The difference in speed, number of times that ants were blown off the trail, and the transition time were lower for large ants. Accordingly, in windy conditions the mean ants? size was larger than in windless conditions (mean ± SE: 5.2 ± 0.06 and 4.2 ± 0.07 mm, respectively). Our results suggest that leaf-cutting ants can reduce the negative effect of wind by increasing the size of ants assigned to foraging. These results illustrate how social organisms can collectively mitigate the negative effect of environmental factors.