Structure and physiology of the ant ocelli

Most flying insects possess single lens eyes known as ocelli that assist in flight, navigation and also have an indirect role in foraging. In this thesis, I studied the ocelli of pedestrian ants by characterising the anatomy of the ocelli in three species of desert ants and physiologically measuring the visual properties of the ocelli in day- and night-active Myrmecia ants. I found that the Saharan desert ants had a fused rhabdom and anatomical features that would make them polarisation sensitive. The Australian desert ant, M. bagoti had an unusual ocellar retina with open rhabdoms wherein each retinula cell contributed microvilli in more than one orientation, making them unlikely to bepolarisation detectors. In Myrmecia, I measured the contrast sensitivity and spatial resolving power of the ocellar second order neurons. I found that in all species when both the compound eyes and ocelli were exposed to the visual stimuli, the compound eye contributed significantly to the ocellar second order neurons. However, when the compound eyes were occluded the response from the ocellar second order neurons was not quantifiable, which made it difficult to measure the visual properties of the ocelli. I discuss these anatomical and physiological findings in the ecologically relevant conditions that each species encounters.