Miniaturisation of sensory systems in ants

The main focus of this thesis is the study of sensory systems in the context of changing body-size. In particular the study of ant sensory systems and how these are shaped by miniaturisation. The study of insect visual ecology and physiology is used as a basis to develop a framework for the study of ant antennal sensilla and chemosensation, to interpret anatomical variation from a functional and organ design perspective. This thesis reviews the anatomy and nomenclature of antennal sensilla through two case studies on an extremely large species Myrmecia pyriformis and a small species Temnothorax rugatulus. These two studies additionally quantify intraspecific variation and discuss the potential functional consequences of this variation for self-organising insect societies and task allocation. A large scale comparative study takes the tools developed in previous chapters to focus in on how chemosensilla vary in their numbers, size and distribution through the Fomicid phylogeny. The gross anatomy of the antenna and changes in shape from club to filiform antennae are described in detail. Anatomical data are analysed to identify scaling trends and potential adaptations driven by miniaturisation. Ecological and phylogenetic considerations are discussed wherever relevant. The wide ranging impacts of body size changes are reviewed, incorporated into the interpretation of results and used to propose promising avenues for future research. Finally, ant body size and some of the different methods used in the literature to measure size and size variability are critically analysed. The functional implications of body size variability within species are discussed using Iridomyrmex purpureus as an example. This thesis makes use of a variety of microscopy techniques. In addition to the methods sections of each chapter a dedicated methods chapter is included. This chapter reviews some of the techniques used in the main data chapters and in the additional publications produced over the course of this thesis

From Large to Small, from Day to Night: The Sensory Costs of Miniaturisation in Ants

This Honours thesis examines sensory adaptations of the compound eyes and antennal sensilla in response to diminishing body size and photic niche. It examines four different ant species using scanning electron microscopy and histological techniques

Techniques for investigating the anatomy of the ant visual system

This article outlines a suite of techniques in light microscopy (LM) and electron microscopy (EM) which can be used to study the internal and external eye anatomy of insects. These include traditional histological techniques optimized for work on ant eyes and adapted to work in concert with other techniques such as transmission electron microscopy (TEM) and scanning electron microscopy (SEM). These techniques, although vastly useful, can be difficult for the novice microscopist, so great emphasis has been placed in this article on troubleshooting and optimization for different specimens. We provide information on imaging techniques for the entire specimen (photo-microscopy and SEM) and discuss their advantages and disadvantages. We highlight the technique used in determining lens diameters for the entire eye and discuss new techniques for improvement. Lastly, we discuss techniques involved in preparing samples for LM and TEM, sectioning, staining, and imaging these samples. We discuss the hurdles that one might come across when preparing samples and how best to navigate around them.This work was supported by a graduate scholarship to FRE and grants from the Australian Research Council (DE120100019, FT140100221, DP150101172)

Functional anatomy of the worker honeybee stinger (Apis mellifera)

Summary: The honeybee stinger is a powerful defense mechanism that combines painful venom, a subcutaneous delivery system, and the ability to autotomize. It is a complex organ and to function autonomously it must carry with it all the anatomical components required to operate. In this study, we combined high-speed filming, SEM imagery, and micro-CT for volumetric rendering of the stinger with a synthesis of existing literature. We present a comprehensive description of all components, including cuticular elements, musculature, nervous and glandular tissue using updated imagery. We draw from the Hymenoptera literature to make interspecific comparisons where relevant. The use of 3D reconstruction allows us to separate stinger components and present the first 3D renders of the bee stinger including the terminal abdominal ganglion and its projections. It also clarifies the in-situ geometry of the valves within the bulb and the spatial relationships among the accessory plates and accompanying musculature

Subtle changes in the landmark panorama disrupt visual navigation in a nocturnal bull ant

The ability of ants to navigate when the visual landmark information is altered has often been tested by creating large and artificial discrepancies in their visual environment. Here, we had an opportunity to slightly modify the natural visual environment around the nest of the nocturnal bull ant Myrmecia pyriformis. We achieved this by felling three dead trees, two located along the typical route followed by the foragers of that particular nest and one in a direction perpendicular to their foraging direction. An image difference analysis showed that the change in the overall panorama following the removal of these trees was relatively little. We filmed the behaviour of ants close to the nest and tracked their entire paths, both before and after the trees were removed. We found that immediately after the trees were removed, ants walked slower and were less directed. Their foraging success decreased and they looked around more, including turning back to look towards the nest. We document how their behaviour changed over subsequent nights and discuss how the ants may detect and respond to a modified visual environment in the evening twilight period.10 page(s

The antennal sensory array of the nocturnal bull ant Myrmecia pyriformis

Insects use antennal sensilla to not only detect chemical and mechanical cues but also to sense changes in temperature, humidity and CO2 levels. Very little is known about the variation in numbers, size and structure of sensilla in ants. Here we describ

View from a fish eye lens (a) before and (b) after tree removal. from Subtle changes in the landmark panorama disrupt visual navigation in a nocturnal bull ant

Figure S1. View from a fish eye lens (a) before and (b) after tree removal. (a) Three trees (T2, T3, T4) marked with an ‘X’ were removed. A hypothetical path (in green) from the nest (yellow circle) to the main foraging tree T1 is shown

Compound eye and ocellar structure for walking and flying modes of locomotion in the Australian ant, Camponotus consobrinus

Ants are unusual among insects in that individuals of the same species within a single colony have different modes of locomotion and tasks. We know from walking ants that vision plays a significant role in guiding this behaviour, but we know surprisingly little about the potential contribution of visual sensory structures for a flying mode of locomotion. Here we investigate the structure of the compound eye and ocelli in pedestrian workers, alate females and alate males of an Australian ant, Camponotus consobrinus, and discuss the trade-offs involved in optical sensitivity and spatial resolution. Male ants have more but smaller ommatidia and the smallest interommatidial angles, which is most likely an adaptation to visually track individual flying females. Both walking and flying forms of ants have a similar proportion of specialized receptors sensitive to polarized skylight, but the absolute number of these receptors varies, being greatest in males. Ocelli are present only in the flying forms. Each ocellus consists of a bipartite retina with a horizon-facing dorsal retina, which contains retinula cells with long rhabdoms, and a sky-facing ventral retina with shorter rhabdoms. We discuss the implications of these and their potential for sensing the pattern of polarized skylight.10 page(s

The sensory arrays of the ant, Temnothorax rugatulus

Individual differences in response thresholds to task-related stimuli may be one mechanism driving task allocation among social insect workers. These differences may arise at various stages in the nervous system. We investigate variability in the peripheral nervous system as a simple mechanism that can introduce inter-individual differences in sensory information. In this study we describe size-dependent variation of the compound eyes and the antennae in the ant Temnothorax rugatulus. Head width in T. rugatulus varies between 0.4 and 0.7 mm (2.6-3.8 mm body length). But despite this limited range of worker sizes we find sensory array variability. We find that the number of ommatidia and of some, but not all, antennal sensilla types vary with head width. The antennal array of T. rugatulus displays the full complement of sensillum types observed in other species of ants, although at much lower quantities than other, larger, studied species. In addition, we describe what we believe to be a new type of sensillum in hymenoptera that occurs on the antennae and on all body segments. T. rugatulus has apposition compound eyes with 45-76 facets per eye, depending on head width, with average lens diameters of 16.5 μm, rhabdom diameters of 5.7 μm and inter-ommatidial angles of 16.8°. The optical system of T. rugatulus ommatidia is severely under focussed, but the absolute sensitivity of the eyes is unusually high. We discuss the functional significance of these findings and the extent to which the variability of sensory arrays may correlate with task allocation.We acknowledge funding support for a PhD scholarship (FRE) from The Australian National University, from the Australian Research Council's (ARC) Centres of Excellence Scheme (CEO561903, JZ & AN), from the Go8 Australia Germany Joint Research Cooperation Scheme (AN & JZ), ARC DECRA and Future Fellowship Grants to AN (DE120100019, FT140100221) and from the National Science Foundation for NEL's PhD stipend (NSF DGE-1143953)