Vision and navigation in nocturnal ants

Abstract

The ability to navigate between places of importance is fundamental for all animals be it for foraging on a daily basis or for migrating seasonally from and to mating or feeding grounds. Central-place foragers, such as ants, have to regularly navigate between their nest and food sources every day, often covering 1000 times their body length. Ants have occupied almost every environment on earth, from barren deserts to the dense understory of rainforests and they are active during both day and night. The navigational cues available in these different environmental and temporal niches are radically different. This makes it possible to study the mechanisms underlying navigation in both closely and distantly related species by comparing (1) their reliance on different navigational cues between different niches, (2) how their sensory systems have adapted to perceive and capture the information they need and (3) how their brains process the information, which ultimately drives behaviour. This combination of the disciplines of ethology, evolutionary biology and neuroscience is commonly referred to as neuroethology and aims at studying the mechanisms underlying animal behaviour in the context in which they have evolved. Ants repeatedly return to places of interest by first memorising the visual scene around it. On their return trips they move and compare their current views to a stored memory image to pinpoint specific locations. For this, animals require a stable image. The robustness of visual information needed to compare memorised and current views is prone to degradation by both locomotion-induced blurring and also by environmental factors such as falling light levels. In the first part of my thesis, I address how nocturnal bull ants, Myrmecia pyriformis, stabilise their head to varying degrees of locomotion-induced body roll at a range of light intensities. I demonstrate through experiments in the animals' natural habitat and in laboratory conditions using highspeed videography that their ability to stabilise their head decreases as light levels drop. This clearly indicates that vision plays a role in head stabilisation in these ants. I discuss the consequences of imperfect head roll for visually guided navigation. In the second part of my thesis I describe techniques in histology, neuroanatomy and behavioural ecology that I learnt to understand the underlying mechanisms of navigation in nocturnal ants. Show more