Visual navigation and physiology in Australian bull-ants and stingless bees

Australian bull-ants, from the genus Myrmecia and stingless bees, from the genus Tetragonula and Austroplebeia, are sympatric species that differ widely in their modes of locomotion. The visual ecology of a walking Myrmecia ant is drastically different from that of a flying stingless bee. In addition to differences in their modes of locomotion, their body size varies too (Myrmecia: 8-30mm in body length, stingless bees: ~4mm body length), which places constraints on the design of their visual systems. In both species foragers engage in a range of visually guided behaviours including navigating through their environment in search of food, locating their home, nest defence and avoiding predators. Both these bees and the ants possess compound eyes and ocelli that enable them to engage in visually guided behaviours.

In this thesis, I investigated the visual navigation and physiology of a diurnal-crepuscular ant Myrmecia tarsata and two Australian stingless bees: Austroplebeia australis and Tetragonula carbonaria. First, I studied the homing ability of M. tarsata released on an air-cushioned trackball in familiar locations around its nest and in an unfamiliar location. Second, I explored the physiological interactions between compound eyes and ocelli in Myrmecia ants. Finally, I physiologically measured the visual properties of the compound eyes of A. australis and T. carbonaria. In my behavioural investigations I found that ants adjusted their bearings as they travelled longer virtual path lengths until they were able to find a consistent bearing. I show and discuss that homing ants achieve this even when the visual scene does not get updated as expected. From my physiological investigations, I found that the compound eyes of Myrmecia ants significantly improve the spatial vision of the ocelli, which may provide a basis for efficient navigation. Finally, I found that the larger A. australis invests more in the contrast sensitivity of its compound eyes than the smaller T. carbonaria, although both bees maintain a similar capacity for spatial resolution. Overall, this thesis highlights the behavioural and physiological mechanisms necessary for Australian bull ants and stingless bees to navigate visually in their environment.