Navigation, recruitment, foraging ecology and visual systems of the banded sugar ant, camponotus consobrinus

Abstract

Each species inhabits a unique niche. These niches can be defined by biotic or abiotic factors and animals evolve adaptations and behaviours to successfully exploit their niche. In this study I explore the niche of the Banded Sugar Ant, Camponotus consobrinus. I characterise the daily activity of this species that forages along the branches of Eucalyptus trees, a complex 3D environment. This species is crepuscular/nocturnal thus exposed to both dim and bright ambient light conditions, and appears to time outbound foraging activity to sunset throughout the year, although much less rigidly coupled compared to previously studied sympatric Myrmecia pyriformis. Activity onset occurs as a burst in outbound foragers during sunset and twilight periods, with few individuals returning to and leaving the nest during the night. Most individuals return to the nest in the morning, as sunrise approaches. I conducted temperature tolerance experiments with the aim of testing whether temperature might be an additional factor affecting the activity onset in this species. Through displacement experiments I show that both inbound and outbound foragers exclusively attend to landmark information for navigation and my experiments demonstrate for the first time a species of ant that does not rely on path integration for navigation or a celestial compass. Interestingly, however, the search patterns of displaced foragers do clearly involve path integration. Camponotus consobrinus recruits by tandem running where a recruit closely follows a leader. I characterise this behaviour and show by displacing recruits that they attend to landmark information for navigation, as well as that recruited individuals can also be experienced foragers. Further, I document dynamically changing tandem pairs, that is, apparently solitary foragers joining a tandem leader if her previous recruit has lost contact. Lastly, I examine the functional anatomy of the apposition compound eyes of C. consobrinus with the aim of identifying adaptations that allow these ants to operate at extremely varying light levels. C. consobrinus possess large diameter rhabdoms (7.32um) typical of night-active hymenoptera, but comparatively small facet lenses (20.81 - 25.56um). Light flux to the rhabdom is controlled by a variable primary pigment cell pupil that narrows the light path to less than 1um diameter at high light intensities. I further present initial findings of newly emerged ants that show an almost complete lack of screening pigment granules in both pigment and retinular cells C. consobrinus possess an unusually prominent dorsal rim area (DRA) with very large modified, non-twisting rhabdoms that are very likely to be polarization sensitive. However, I could not find evidence for the use of a polarization compass in this species. The results of experiments in which I occluded the DRA or the rest of the compound eye indicate that the DRA may mediate canopy orientation. I discuss C. consobrinus activity patterns, navigational mechanisms, compound eye adaptations and their recruitment strategy in the light of their association with foraging trees, the navigational information content of their environment and possible reasons for the particular temporal niche in which these ants are active.