The Evolution of Flight in Insects: Reconstruction and Biomechanical Analysis of a Protopterygote Insect Ancestor

Abstract

Powered flight in insects has allowed them to become one of the most successful groups of organisms on the planet. How they evolved to become flyers from non-flyers over 400 mya remains a mystery. Few published works have experimentally attempted to explore how flight may have arisen in insects and as such, the objective of this thesis is to attempt to define a possible protopterygote insect and its pathway to selection for powered flight. Here, I have employed a combination of behavioural analysis on an extant basal group insects and allometric scaling of morphology to define and construct a likely protopterygote insect. I have also enacted biomechanical methods such as force measurement and flow visualization on a physical wingless, static winged and a mechatronic (dynamic) flapping protopterygote model to explore potential elements for the selection of flight in insects. I have found that body shape (posture) is important to increasing drag as evidenced by the decreasing descent velocity and self righting ability of the Archaeognatha (Chapter 2), while their unique jumping behaviour can be useful to escape from the confines of standing water, likely present during the time of the protopterygote insect (Chapter 3). Biomechanical testing has revealed the presence of a low pressure zone behind the dorsum of a protopterygote model emulating the posture of falling Archaeognatha (Chapter 5) and that flapping can increase drag within the Reynolds regime of the putative protopterygote (Chapter 6) potentially setting the stage for thoracic wing selection. My thesis undertakes a novel approach, contributes empirical data and new insights to an emerging theory of the evolution of flapping flight in insects. This theory draws on previously defined hypotheses and attempts to combine elements from each while also providing support for the likelihood of a falling, flapping protopterygote insect contributing to selection for powered flight in insects.