Nest architecture in polydomous grass-cutting ants (Acromyrmex balzani)

Abstract

Acromyrmex balzani is a grass-cutting ant species frequently found in Cerrado areas. However, little is known about the architecture of the polydomous nests of this ant. Fifteen A. balzani nests located in a cerrado region in Botucatu, São Paulo, Brazil, were studied. The polydomous nests were studied in three ways. First, we investigated the architecture in nests moulded with cement and without moulding. Second, we performed an aggressiveness test among workers in different subnests and nests. Third, we excavated the nest and collected the colony to measure the population, verifying the existence or not of a queen in all nests. A cement mould was made of seven nests to permit better visualization of internal structures such as chambers and tunnels. Eight nests were excavated without moulding and white neutral talc was used to highlight the parts of the nests. After excavation, the depth and dimensions (length, width and height) of the chambers were measured. The results showed that the nests had a single entrance hole whose structure consisted of straw and other plant residues in winter. Mounds of loose soil, if present, were found 6-48 cm from the hole. The number of chambers containing fungus ranged from one to five, with the first being found a few centimetres beneath the ground surface (4 cm) and the last up to a maximum depth of 160 cm. The length of the tunnels ranged from 12 to 28 cm. These tunnels were built in a vertical or inclined position, leading to the chambers. No waste chambers were found, with the waste being deposited externally. Additionally, the polydomous nests contained one to eight subnests. In the aggressiveness test, when concolonial workers were confronted, no aggressiveness was observed. In contrast, when allocolonial workers were confronted, there was a high incidence of aggression among them. Excavation of polydomous nests showed only one queen for each polydomous nest, i.e. subnests with a single queen. Our study contributes to a better understanding of the so far unknown nest architecture of the polydomous grass-cutting ant A. balzani.

Ant nesting ecology of leaf-cutter ants in altitude natural fields, southern Brazil

“…These results are in line with the results observed in this study (Table 2). In a study by Caldato et al (2016) in anthills of the species Acromyrmex balzani, they presented an irregular shape, thus differing from the results found in our study. These observations demonstrate the particularities between the genera of leaf-cutting ants and within the species themselves in relation to the architecture of their anthills.…”

“…These observations demonstrate the particularities between the genera of leaf-cutting ants and within the species themselves in relation to the architecture of their anthills. According to Caldato et al (2016), these differences in the architecture of the anthills are closely related to the edaphoclimatic conditions of a given region. In this way, the observations made in this work on architecture of the anthills of both genera Atta and Acromyrmex can be particularized due to the unique conditions of climate, relief and vegetation existing in the region comprised by the altitude fields.…”

Nest Architecture and Animals Associated with Neoponera verenae (Forel) (Formicidae, Ponerinae)

“…Dusters are commonly used to pump poison powder into the nests of Atta and Acromyrmex species and the same dusters were also effective for pumping neutral talc into the nests of N. verenae. This strategy facilitated the visualization of tunnels and how they are connected to the chambers (Caldato et al, 2016).…”

“…The excavation was completed when it was noted that there were no more deep chambers or tunnels. During the excavation process, we measured the height, width and length of the chambers as well as the diameter of the inlet and/or outlet (Antonialli-Junior & Giannotti, 1997;2001;Caldato et al, 2016) and we made a sketch, in scale, considering the shape and arrangement of the chambers and tunnels of each nest.…”

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

“…We suggest that in Acromyrmex, selective pressures acting on temperature and humidity control led to nesting habits closer to or above the soil surface and to the evolution of architectural innovations that improved gas exchanges. occurs in all species of the genera Amoimyrmex [15], Atta [3], and at least seven Acromyrmex species [25,[28][29][30]. In these groups, colonies grow by extending both deeper and laterally from the location of the founding chamber, and the excavated chambers always branch off the connecting tunnel via a single peduncle (figure 1).…”