Maior demanda do fungo, maior atividade: testando o modelo de limiar de resposta na atividade de forrageamento de Acromyrmex subterraneus (Hymenoptera, Formicidae)

Abstract

Task allocation is a classic example of decentralized organization, where workers make individual decisions about task adherence based on environmental clues and internal responsiveness thresholds. According to the Response Threshold (RT) model, ant workers differ in their sensitivity to task-related stimuli, resulting in an unequal involvement between individuals. This behavioral plasticity can be tested in leafcutter ants, for example Acromyrmex subterraneus, to investigate how the intensity of a stimuli, like the reduction of the fungus garden, affect the recruitment of additional workers, supposedly those with higher thresholds, to the affected task, ensuring that essential tasks such as foraging and the cultivation of the fungus occur uninterruptedly. Our study investigated how the reduction in fungus garden volume impacted the foraging dynamics and the efficiency in A. subterraneus. The study was conducted with six colonies maintained in the myrmecology laboratory at UFJF. Experimental tests were conducted before and after standardized manipulation where 50% of the fungus garden was removed, maintaining a constant population size. Each colony was connected to a foraging arena supplied with 10 g of fresh leaves. We registered the flow of workers inbound and outbound (with and without leaf fragments), the foraging latency (delay) and the individual efficiency of transport. Our results were significant, with a decrease in delay accompanied by an increase in foraging flow following the reduction of the fungus, when compared to control conditions. Additionally, individual foraging efficiency also increased significantly, with workers being faster in the reduction treatment, suggesting that colonies not only intensified foraging activity but also improved transport performance per worker. These findings highlight that the colony is prepared to respond to changes in fungus demand, ensuring a continuous supply of substrate to the fungus garden while maintaining the task execution chain. Our results are consistent with the predictions of response threshold theory and stimulus-driven task allocation models.