Acorn Ants May Create and Use Two Entrances to the Nest Cavity

Sexual Offspring Production by Acorn Ant Temnothorax crassispinus Colonies Is Associated with the Colony Size but Not with the Volume of the Nest Cavity

Nest sites are important for ants, as the nests provide refuge against enemies and ensure optimal conditions for the brood development. As the construction of a nest is a time and energy consuming activity, many ant species dwell in ready-for-use cavities. For them, choosing a good nest site is important, as the quality of nest site could affect factors such as the energy allocation and production of sexual individuals. Ants of genus Temnothorax inhabit cavities in, e.g., acorns and twigs, and these ant colonies prefer larger cavities as nest sites. It was previously shown that colonies inhabiting more durable nest sites invested more resources in sexual production. The aim of this study was to find out whether the volume of a nest cavity influences the sexual offspring production of acorn ant Temnothorax crassispinus colonies. For this purpose, a three-month long laboratory experiment was performed. Colonies of the Temnothorax ant were kept in artificial nest cavities differing in volume. It was found that there was no correlation between the productivity per capita and the colony size. More populous colonies produced more sexual individuals; however, we found no statistical difference in the production of sexual individuals between the colonies that inhabited cavities of different volumes.

Slit in a Nest Site Influences the Nest Site Selection in Cavity Nesting Ant Colonies

For ants, nests provide a refuge against predators and protection from environmental factors. Thus, choosing a good nest site is important for an ant colony, but nest sites are limited resources. Ants of the genus Temnothorax inhabit small cavities in, e.g., acorns, twigs and under rocks. Earlier, it was shown that the ants are able to choose a superior site. In this study, using binary choice tests, we studied the nest site selection by Temnothorax crassispinus ant colonies that typically inhabit empty acorns. For this purpose, we used artificial nest sites without and with an additional slit in the nest wall, mimicking the cracks in potential nest sites under natural conditions. We found that the ant colonies preferred artificial nest sites without these slits. However, no difference in the number of colonies inhabited nest sites with a slit vs. those without a slit was found when the slits were closed using transparent food foil, which prevented the air flow while keeping an inflow of light. What is more, additional light through the hole in the red filter covering the artificial nest sites had no influence on the nest site selection. The results of this study suggest that the air flow through a slit in the nest site wall, rather than additional light, influences the nest site selection. The absence of cracks, e.g., in acorns, could be an indication of the durability of potential nest sites. Thus, choosing a cavity without such damage could be beneficial for the ant colonies.

Emergent regulation of ant foraging frequency through a computationally inexpensive forager movement rule

Ant colonies regulate foraging in response to their collective hunger, yet the mechanism behind this distributed regulation remains unclear. Previously, by imaging food flow within ant colonies we showed that the frequency of foraging events declines linearly with colony satiation (Greenwald et al., 2018). Our analysis implied that as a forager distributes food in the nest, two factors affect her decision to exit for another foraging trip: her current food load and its rate of change. Sensing these variables can be attributed to the forager's individual cognitive ability. Here, new analyses of the foragers' trajectories within the nest imply a different way to achieve the observed regulation. Instead of an explicit decision to exit, foragers merely tend toward the depth of the nest when their food load is high and toward the nest exit when it is low. Thus, the colony shapes the forager's trajectory by controlling her unloading rate, while she senses only her current food load. Using an agent-based model and mathematical analysis, we show that this simple mechanism robustly yields emergent regulation of foraging frequency. These findings demonstrate how the embedding of individuals in physical space can reduce their cognitive demands without compromising their computational role in the group.