Student Theses and Dissertations

Waring Trible

Date of Award

2020

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

RU Laboratory

Kronauer Laboratory

Abstract

Ants are social organisms that live in groups and depend intimately on their nestmates for growth and survival. Ants have evolved a number of highly sophisticated, social phenotypes that allow them to form coherent colonies. This thesis explores two particularly derived features of ant biology: complex chemical communication and caste plasticity. To study these features, I had a particular focus on generating and characterizing germ-line mutants. I believe that the study of mutants, and applying molecular biology methods more generally, can lead to insights in ant biology that would not be possible with more traditional methods. I first describe my efforts to develop a CRISPR protocol to make the first germ-line mutant ant lines. I conducted this work using a unique, clonal ant species, Ooceraea biroi, that has many properties making it favorable for laboratory genetics studies. Establishing this protocol required a multi-year optimization process to account for many of the particular features of ant biology, such as egg production and incubation, growing and maintaining lines, and optimizing experimental treatments to produce high mutagenesis rates. I next describe the mutants I generated using these methods, null mutants of a highly conserved insect protein called orco. Orco, or olfactory receptor co-receptor, is required for the function of an important class of chemosensory proteins, the odorant receptors, in insects. I created orco mutant ants and found that they have striking deficiencies in their social behavior and fitness, including an inability to nest with other ants or follow chemical pheromone trails and severely reduced life span and fecundity. These results supported the growing consensus that odorant receptors are key chemosensory proteins for pheromone perception in ants, and provided a new window into ant social behavior and collective organization. Unexpectedly, and unlike orco mutants in other types of insects, I also found that orco mutant ants have severe neuro-anatomical deficiencies, including a loss of most antennal lobe glomeruli and sensory neurons in the antenna. This surprising result implies that orco may play an important role in antennal lobe morphology in ants, and could provide insights into the development and evolution of complex olfactory systems. The following chapter is a critical literature review of the development and evolution of morphological castes, such as workers and queens, in ants. I describe a stereotyped and previously overlooked pattern of morphological variation in ants, and illustrate how this pattern may provide some early insights into the molecular mechanisms of caste plasticity. This chapter provides a falsifiable, mechanistic framework for caste development and suggests a route to start looking for the actual molecules that regulate this interesting process. Finally, I start to realize this promise by characterizing a caste mutant in the laboratory. I discovered a spontaneous ‘winged mutant’ that belongs to one of the known clonal lineages of O. biroi and aberrantly expresses queen-like morphology and behavior at worker-like body sizes. These mutants bear a striking resemblance to one class of ant species with derived caste systems, the recurrently evolved workerless social parasites. They could thus provide a window into the mutations that give rise to these unique ants. Overall, this thesis represents the first characterization of mutant lines in ants, and I hope it demonstrates how this approach can be used to generate robust conclusions about ant biology.

Comments

A Thesis Presented to the Faculty of The Rockefeller University in Partial Fulfillment of the Requirements for the degree of Doctor of Philosophy

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