Desert ant (Melophorus bagoti) dumpers learn from experience to improve waste disposal and show spatial fidelity

Abstract

The Central Australian red honey-pot ant Melophorus bagoti maintains non-cryptic ground-nesting colonies in the semi-desert habitat, performing all the activities outside the nest during the hottest periods of summer days. These ants rely on path integration and view-based cues for navigation. They manage waste by taking out unwanted food, dead nestmates, and some other wastes, typically depositing such items at distances > 5 m from the nest entrance, a process called dumping. We found that over multiple runs, dumpers headed in the same general direction, showing sector fidelity. Experienced ants dumped waste more efficiently than naive ants. Naive individuals, lacking prior exposure to the outdoor environment around the nest, exhibited much scanning and meandering during waste disposal. In contrast, experienced ants dumped waste with straighter paths and a notable absence of scanning behaviour. Furthermore, experienced dumpers deposited waste at a greater distance from the nest compared to their naive counterparts. We also investigated the navigational knowledge of naive and experienced dumpers by displacing them 2 metres away from the nest. Naive dumpers were not oriented towards the nest in their initial trajectory at any of the 2m test locations, whereas experienced dumpers were oriented towards the nest at all test locations. Naive dumpers were nest-oriented as a group, however, at the test location nearest to where they dumped their waste. These differences suggest that in red honey ants, learning supports waste disposal, with dumping being refined through experience. Dumpers gain greater spatial knowledge through repeated runs outside the nest, contributing to successful homing behaviour. Simple SummaryEusocial insects maintain hygiene in their nests with cleaning behaviours. One such behaviour is the disposal of refuse material, food waste, dead nestmate bodies, and other waste, outside the nest. This study on the waste disposal behaviour of Central Australian red honey-pot ants, Melophorus bagoti, provides valuable insights into the significance of learning in waste disposal. Naive ants improved over five consecutive runs in waste dumping, running straighter paths with less scanning. The observed differences between experienced and naive ants in waste dumping imply that learning contributes to more streamlined and less time-consuming waste management. In addition, dumping ants established sector fidelity in the consecutive runs, heading mostly in the same general direction on each dumping trip. This behaviour reduces the amount of navigational expertise that the dumper has to acquire. Learning in individuals thus helps an ant colony to cope with not only navigational challenges in foraging, which have been well studied in this and other desert ant species, but also with other demands of living in a harsh desert habitat.