Abstract
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). 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. 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.
Highlights
The leaf-cutting ants appear to be a suitable group for studying the effect of global warming on ectothermic animals
The climate change concept refers to a modification in the state of the climate that is identifiable by an alteration in the mean and/or in the variability of its properties that persists for a prolonged period of time, measured in hundreds of years (IPCC 2007)
All ten forage items used in the study were harvested in greater proportion under heat treatment (Figure 4A,B,C, D,E,F,G,H,I,J), and significant differences between treatments were found in four of them: Diplotaxis tenuifolia (W = 95, p = 0.0026) (Figure 4B); Olea europaea shoot (W = 99, p = 0.0003) (Figure 4D); Rhynchosia senna (W = 90, p = 0.0207) (Figure 4G); Schinus molle mature (W = 87, p = 0.0457) (Figure 4H)
Summary
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. Under scenario A2, the temperature shows a positive tendency for all geographic areas ( there is seasonal variation); a marked N-S (north-south) gradient is seen with an increase in mean annual temperature of between 4°C and 4.5°C for the N of Argentina and between 2.5°C to 3°C and 2°C to 2.5°C for the center and S respectively, whereas for the Andes, there is a N-S gradient between 4.5° and 2°C. A common approach, seen in work on insects of the effects of temperature on their behavioral habits and physiological processes, is the study of functions such as locomotion (flight) and reproduction or growth rate (May 1979; Bale et al 2002). Habits that are linked to variation in temperature are the way they search for food and other forms of locomotion, e.g., walking over the ground (Vogt et al 2003; Angilletta et al 2008; Jumbam et al 2008)
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