A fully segmented body and jointed legs are defining characteristics of the Arthropoda (Insecta, Crustacea, Myriapoda, and Chelicerata). The underlying mechanisms involved in achieving these features are not well understood outside of the insect Drosophila melanogaster (fruit fly) – a long germ band organism where segmentation occurs all at once in a syncytial blastoderm. In the more common, ancestral mode of development, short germ band, new segments are added sequentially from the cellular environment of a posteriorly extending growth zone. Segmentation in these organisms may not always be comparable to the “Drosophila paradigm” and, therefore, require further analysis. My thesis will explore the conservation and divergence of the molecular mechanisms of segmentation in a phylogenetically basal, short germ band insect, Periplaneta americana (American cockroach). Presented over three results chapters, I will discuss aspects of cockroach segmentation processes, from the establishment of a posterior organiser and growth zone, to subsequent posterior growth and the formation of new segments. In particular, Chapter III describes how interactions between the Cad/Wnt-dependent posterior organiser and the Notch-segmentation clock control posterior growth and segmentation. Chapter IV encompasses the expression patterns and potential roles for Periplaneta homologues of the pair-rule genes: even-skipped, runt, pairberry, and sloppy-paired throughout embryogenesis, identifying deviations in function between anterior and posterior segmentation processes. New functions for the non-canonical, polycistronic small Open Reading Frame (smORF) gene tarsal-less in body patterning are discussed in Chapter V, along with the conserved roles for tarsal-less, nubbin, Notch, and Delta in leg and development. Elucidation of the networks involved in these processes will help establish putative ancestral gene functions allowing us to gain further insights into the evolution of insect (and arthropod) body segmentation and leg joint formation.

Visually guided navigation presents the perfect arena for studying the relationship between brain, body and environment and the behaviour which emerges from their interaction. It is a behaviour seen across the animal kingdom, from desert ants to humans, offering the possibility of common underlying computational principles. In addition, it represents an important applied problem: how to get robots to navigate reliably in situations where other kinds of information are lacking or absent. This thesis examines the problem of visual navigation in insects at different levels of abstraction using computational modelling, showing the power of this approach in describing and explaining insect behaviour, with a focus on image-based homing methods. It begins with an examination of an exploratory behaviour performed by naive foraging ants, known as ‘learning walks', and how the relationship between the shape of the learning walk and the visual form of the environment together determine homing success. I then proceed to look at the information carried by the visual receptive fields associated with a small number of neurons (of two classes) in Drosophila, showing that this corresponds to behavioural performance, without requiring any additional black boxes. Finally, I show that simple insect-inspired algorithms also perform well in different applied contexts, such as a flying agent and as a real-world visual compass. The contribution of this thesis is to show the value of computational modelling both in gaining an understanding of complex behaviours, particularly where many variables make more conventional analysis impossible, and in designing real-world applications.

This thesis initially focuses on the chemical ecology of two species of ant which are common in the United Kingdom; Lasius flavus, the yellow meadow ant and Lasius niger, the common black ant. The first data chapter explores the constituent chemicals present in 3 major exocrine glands located in the gaster of L. flavus and discusses their potential functions. The work presented here also highlights the need for the comparative study of the chemical composition of glands. The second data chapter investigates how chemicals present in hindgut extractions of Lasius niger vary with the temporal caste they belong to (nurse or forager), and subsequently looks at how those chemicals may be suited to the tasks performed by that caste. The third data chapter describes the development of a highly sensitive methodology to identify low-concentration pheromones that uses a combination of analytical chemistry and behavioural bioassays. This methodology was used to identify two attractive pheromones of L. flavus, one is a trail pheromone used during foraging while the other is an alarm pheromone used to warn nest-mates of danger. The trail pheromone is the lowest concentration pheromone to be successfully identified in ants to date. This chapter also highlights the need to perform comparative behavioural bioassays to demonstrate the true function of putative pheromones. The final data chapter then investigates the source of alarm signals in Nasutitermes corniger termites and assesses the differential responses of workers and soldiers. This chapter then goes on to elucidate the colony-level effects of alarm on the regularity of repairs made to experimentally manipulated foraging galleries.

The morphogenesis of tissues in animal development is orchestrated by intercellular signalling and executed by cell behaviours such as changes to shape. Understanding the link between signalling and cell shape changes is a key task of developmental biology. This work addresses this problem using the development of the pupal wing of Drosophila melanogaster. The pupal wing is a bilayered epithelium which is patterned into vein and intervein domains, and which secretes the cuticle of the adult wing. I first address the cellular basis of pupal wing development, and show that the process comprises a series of dynamic cell shape changes involving alterations to the apical and basolateral surfaces of the cells. Using temporally controlled mis-expression, I then investigate the role of intercellular signalling in these shape changes, and define the competence of cells in the wing to respond to ectopic signals. The dimensions of signalling in the pupal wing are then investigated, and I show that while BMP ligands can travel between the layers to promote vein development, such signalling is not a prerequisite for cellular differentiation. Within the plane of the epithelium, the BMP ligand Dpp can only induce signalling at a short range, potentially due to the upregulation of receptor levels in receiving cells. Finally, attention is turned to the means by which cell signalling controls cell shape changes, specifically in the crossveins. I identify the RhoGAP Cv-c as a downstream target of BMP signalling which acts to inhibit a novel RhoGTPase function in intervein development. This provides an example of how signalling pathways can enact cell shape changes, via the transcriptional regulation of RhoGAPs.

Thesis (Ph. D.)--University of Wyoming, 2006. / Title from PDF title page (viewed on Dec. 15, 2007). Includes bibliographical references.

Bibliography: leaves 109-126.

Thesis (Ph. D.)--University of Rhode Island, 2005. / Typescript. Includes bibliographical references (leaves 97-106).

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1982. / Vita. Abstract. Includes bibliographical references (leaves 95-101). Also available via the Internet.

Thèse de doctorat : Sciences naturelles : Faculté des sciences de Paris : 1853. / Titre provenant de l'écran-titre. Références bibliogr.

Thèse : Zoologie : Faculté des sciences de Paris : 1859. / Titre provenant de l'écran-titre.