The evolution and development of the insect egg and ovary

Abstract

Life comes in many shapes and sizes, and efforts to describe, categorize, and understand this diversity have been a driving force behind biological discovery. Evolutionary developmental biology, or evo-devo, seeks to understand the origins of diversity by investigating evolutionary changes to the developmental process, that in turn lead to novel and complex traits. But the field of evo-devo is at an inflection point. In recent decades, rich and complex datasets have become much more accessible and inexpensive to generate from a wide variety of organisms. The outcome is that we have unprecedented opportunities to investigate the developmental basis of diversity. However, our ability to make robust inferences about developmental evolution will require us to compare data across taxa using statistical methods based in evolutionary theory. In this thesis I investigate the origins of shape and size diversity through the application of evolutionary inference methods to large datasets of morphological and developmental traits. In Chapter 1, I describe the state of the field of evo-devo, and advocate for a shift in the framework often used in analyses, toward one rooted in evolutionary tree-based thinking. Chapter 2 presents a dataset of 10,000 descriptions of insect egg size and shape, assembled using custom software tools to extract descriptions from the published literature. Chapter 3 analyzes this dataset on a phylogenetic tree of insects to test hypotheses about size and shape evolution in relation to ecological and developmental features. Chapter 4 combines egg size data with a dataset of more than 3,000 ovary descriptions to test a longstanding hypothesis about the size and number of offspring. Chapter 5 investigates the evolutionary relationships of a specific lineage of Hawaiian flies in the family Drosophilidae, identifying specific evolutionary shifts in egg and ovary diversification.