#ANTS DIG DUG ARRANGEMENT SERIAL#

the arrangement of the nest chambers and their connections to the outside, evolved to facilitate the ventilatory air exchanges with the outside environment. īeyond the influence of the nest depth on the CO 2 levels inside the fungus chambers, it is an open question whether the underground nest architectures of the different leaf-cutting ant species, i.e. Besides nest depth, it is known that external architectural features, such as the mound shape or the construction of nest turrets might promote gas exchanges through passive, wind-induced nest ventilation mechanisms. Workers also use CO 2 as an orientation cue during nest excavation, avoiding levels of 4% and preferring places with 1% CO 2 for digging, which in the long term would result in the location of the colony at suitable CO 2 levels across the soil profile. As a short-term response, Acromyrmex lundii workers are known to relocate brood and fungus to nest chambers with CO 2 levels ranging from 1 to 3%. Since high CO 2 concentrations are known to negatively influence the respiration rate of the Atta symbiotic fungus at values near 5%, both short-term and long-term responses to avoid increased CO 2 levels are expected to occur. Thus, the concentration of CO 2 inside fungus chambers should be positively related to nest depth, as measured in field nests of Atta leaf-cutting ants. In the long term, it results in a dynamic equilibrium that equals the concentrations of CO 2 and O 2 inside a fungus chamber with those of the local surrounding soil, as far as no other ventilatory mechanisms driving the exchange of air between fungus chambers and the atmosphere are involved. When CO 2 levels in the soil are lower than inside chambers housing fungus gardens, CO 2 moves into the soil phase, yet diffusion would tend to be reversed at increasing nest depths, since levels of CO 2 in the soil phase increase with depth. The direction of such an exchange would depend on the concentration of CO 2 in the soil relative to the concentration inside the chambers.

All chambers of leaf-cutting ant nests exchange respiratory gases with the soil phase via diffusive flows, which strongly depend on the porosity of the soil. Due to the respiration of workers and fungus, considerable amounts of O 2 are consumed and CO 2 produced inside the nest chambers. Especially in colonies of leaf-cutting ants, which cultivate a symbiotic fungus within subterranean chambers using plant fragments harvested by workers. 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.Īnt nests offer protection against predators and climatic extremes, yet they can compromise the air exchanges between the nest inhabitants and the atmosphere.

#ANTS DIG DUG ARRANGEMENT SERIAL#

Serial nests may be constrained depending on the soil CO 2 levels. CO 2 concentrations were below the values known to affect the respiration of the symbiotic fungus, indicating that shallow and thatched nests are not constrained by harmful CO 2 levels. Ventilation in shallow and thatched nests, but not in serial nests, occurred via wind-induced flows and thermal convection. We recognized (i) serial nests, similar to the ancestral type of the sister genus Trachymyrmex, with chambers excavated along a vertical tunnel connecting to the outside via a single opening, (ii) shallow nests, with one/few chambers extending shallowly with multiple connections to the outside, and (iii) thatched nests, with an above-ground fungus garden covered with plant material. We have shown that in the Acromyrmex genus, three basic nest morphologies occur, and investigated the effects of architectural innovations on nest ventilation. Leaf-cutting ant colonies largely differ in size, yet all consume O 2 and produce CO 2 in large amounts because of their underground fungus gardens.

Ants dig dug arrangement