Dissertation

Locomotion Transitions and Sexual Dimorphism: Understanding the Causes of Phenotypic Integration Patterns

Hellert, Spencer M

2019

Overview

Natural selection has produced a spectacular array of anatomical forms that are adapted to a wide range of environments. However, genetic, developmental, and functional factors may integrate an organism’s traits so that selection cannot optimize them independently for a given environment. A tension therefore exists between processes that promote anatomical diversification and those that promote integration. Using geometric morphometric, I how patterns of integration translate to morphological diversity in two important evolutionary transitions: the limb bones involved in the origin of birds from theropod dinosaurs and the dorsal heads of scarab beetles. My results show that integration of the fore- and hind limbs in theropod dinosaurs changed in the transition to flight. The results also indicate that developmental changes were associated with the change in integration and have been inherited by all birds, regardless of whether they retain the ability to fly. This may explain why flightless birds, despite evolving flightlessness independently, have similar forelimb characteristics. Integration patterns in scarab beetle heads support the hypothesis that ancestrally hornless species had a different modular composition than species in which only one sex has horns. Furthermore, different male morphs have different integration patterns, which supports the hypothesis that an identical complement of genes can also produce different phenotypic integration patterns via different developmental processes. Finally, male and female sexually dimorphic beetles have different integration patterns, suggesting that the sexes have independent genetic and developmental control of their head horns. Overall, I found that specific drivers of evolutionary integration can be identified in both modern and fossil taxa using geometric morphometric methods, even when multiple factors contribute to the pattern of integration. I also found that essentially identical complements of genes can result in different integration patterns. Finally, I found that although evolutionary changes in morphology and function can be accompanied by changes in trait integration, shared, conserved, developmental processes can mask the effects of functional influences on integration resulting in shared patterns of integration.

• Publisher: ProQuest Dissertations & Theses
• Subject: Evolution & development / Evolution and Development / Paleontology
• ISBN: 9781392482209, 1392482208