How environments shape ornament morphological evolution: bringing perspective to a century of inconsistent sexual allometry analysis
The diversity of complex morphologies species use for social communication is reflected by their wide range of functions. Many operate as part of either threat displays or facilitate mate choice, while others may perform dual roles. Measuring the extent species disproportionately invest in these sexual morphologies is a primary means of assessing their various adaptive functions. However, this analysis (i.e., allometry) often produces inconsistent outcomes that undermine its effectiveness. To this end, I investigated whether different sexual structures always evolve similar allometric patterns, and how the environment might prevent this from happening. The second chapter evaluates how locomotion in different environments cause related species to evolve variable sexual allometries. Among a highly social group of intertidal Blenniid fish, underwater species were found to invest in markedly smaller ornament allometries compared to their terrestrial relatives, demonstrating inconsistent sexual allometries can be caused by biomechanical restrictions unique to a species environment. For my third Chapter I used a meta-analysis to reveal female preference experiments generally failed to present females with male display structure sizes informed by allometric data. This implies questions central to sexual allometry theory – that female preferences drive the evolution of disproportionately larger male sexual structures – are yet to be formally tested in an experimental setting. I designed such an experiment using realistic models of a terrestrial Blenniid fish species from Chapter two. Its findings indicate, in the absence of environmental constraints, female preferences can support the evolution of disproportionate scaling among sexual allometries. Finally, in Chapter four I expand upon my findings in Chapter two and explore additional ways the environment might restrict sexual allometric relationships. Specifically, its influence upon the visual efficacy of these structures and how this affects allometry patterns. Among Anolis and Draco lizards, light and display distances were found to prevent their ornamental dewlaps from evolving disproportionately large allometric patterns, despite being a known sexually selected structure. Not only do these allometries suggest dewlap size is determined by its surrounding environment, it is also new evidence the dewlap actually functions to improve detection of the overall lizard display. Collectively, it appears attributes of the environment play a long-overlooked role in contributing to problematic inconsistency among sexual allometries. My thesis, however, promotes the utility of allometry to adequately measure the influence of sexual selection acting on display structures, provided they are explained in the context of these environmental limitations.
Summers, Thomas ; https://orcid.org/0000-0002-8743-1545
sexual selection, allometry, mate choice, female assessment, ornaments, animal communication, anzsrc-for: 31 BIOLOGICAL SCIENCES, anzsrc-for: 310405 Evolutionary ecology, anzsrc-for: 310301 Behavioural ecology
Networked Digital Library of Theses and Dissertations