Vol. 53, 2014

The effect of increase in the temperature on the foraging of Acromyrmex lobicornis (Hymenoptera: Formicidae)

Rodrigo Tizón¹*, Juan Pedro Wulff² and Daniel Valerio Peláez³

¹CERZOS-CONICET, CCT-Bahía Blanca, San Andrés 850, Bahía Blanca 8000, Argentina
²Departamento de Biología, Bioq. Y Farm, UNS; CERZOS-CONICET, CCT-Bahía Blanca, San Andrés 850, Bahía Blanca 8000, Argentina
³CIC; CERZOS-CONICET, CCT-Bahía Blanca, San Andrés 850, Bahía Blanca 8000, Argentina

Abstract
Background: The leaf-cutting ants appear to be a suitable group for studying the effect of global warming on ectothermic animals. These ants of the Atta and Acromyrmex genera are considered to be the main herbivores in the Neotropics. They have patterns of harvesting associated with ranges of temperature. Acromyrmex lobicornis has the widest geographical distribution in Argentina. Peak activity has always been recorded in spring and at the beginning of autumn, being slightly lower in summer when they forage at night, and activity ceases almost completely in winter. In order to evaluate how an increase in temperature affects the activity of A. lobicornis, we studied the amount of foraging and the trophic preferences in two treatments under controlled humidity and temperature conditions (Δ4.5°C) and we also measured the walking speed of the workers as a function of an increase in temperature (6°C to 32°C).
Results: The rate of harvesting was 33% higher in the warmer treatment. There was a tendency for the ten forage items evaluated to be harvested at the higher temperature. The trophic preference, with or without heat, showed some variation for different items: the shoots of Olea europaea and the dry Schinus molle were the most harvested with heat and without heat, respectively.
Conclusions: Our results support the hypothesis that the ants’ activity changes at higher temperature, with higher rates of harvesting and a change in walking speed is observed. There is also variation in the trophic preference, selecting plant items with a higher composition of elements that are degradable by symbiotic fungi. The average walking speed of the workers increased gradually as a function of an increase of temperature up to a maximum speed of 2.85 cm/s. Our results suggest that small variations in ambient temperature significantly affect certain behavior patterns in the leaf-cutting ants.

Key words: Acromyrmex lobicornis; Global warming; Locomotor activity; Foraging preferences.

*Correspondence: E-mail: frtizon@criba.edu.ar