Abstract
The Chaco leaf-cutting ant Atta vollenweideri (Forel) inhabits large and deep subterranean nests composed of a large number of fungus and refuse chambers. The ants dispose of the excavated soil by forming small pellets that are carried to the surface. For ants in general, the organisation of underground soil transport during nest building remains completely unknown. In the laboratory, we investigated how soil pellets are formed and transported, and whether their occurrence influences the spatial organisation of collective digging. Similar to leaf transport, we discovered size matching between soil pellet mass and carrier mass. Workers observed while digging excavated pellets at a rate of 26 per hour. Each excavator deposited its pellets in an individual cluster, independently of the preferred deposition sites of other excavators. Soil pellets were transported sequentially over 2 m, and the transport involved up to 12 workers belonging to three functionally distinct groups: excavators, several short-distance carriers that dropped the collected pellets after a few centimetres, and long-distance, last carriers that reached the final deposition site. When initiating a new excavation, the proportion of long-distance carriers increased from 18% to 45% within the first five hours, and remained unchanged over more than 20 hours. Accumulated, freshly-excavated pellets significantly influenced the workers' decision where to start digging in a choice experiment. Thus, pellets temporarily accumulated as a result of their sequential transport provide cues that spatially organise collective nest excavation.
Highlights
Animals have to dispose of the removed soil by transporting it from the underground to the surface [1]
The aim of this study was to characterise the transport of soil pellets in the leaf-cutting ant A. vollenweideri, and to investigate whether soil pellets are temporarily deposited inside the nest and influence the excavation behaviour of nearby workers
Animals and material A. vollenweideri is a widespread species in the Gran Chaco
Summary
Animals have to dispose of the removed soil by transporting it from the underground to the surface [1]. One ant species that has been studied intensely in terms of construction and functionality of external nest architecture is the leaf-cutting ant Atta vollenweideri (Forel) from the Gran Chaco region in South America. Workers of this species usually build turrets on top of the nest openings in the centre of their nest mound. These turrets, which enhance wind-induced nest ventilation [11,12], are mainly built with materials collected from the soil deposits around the nest openings, i.e. materials previously transported to the surface from the underground or collected from adjacent areas [9,13]. The sheer amount of soil colonies of this species move from deeper layers to the surface makes them a major factor shaping the composition of the vegetation in the Gran Chaco region [16,17,18,19]
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