The role of cuticular hydrocarbons in determining male reproductive success
Lane, Sarah Marie
Thesis or dissertation
University of Exeter
Reason for embargo
We wish to publish from this thesis.
Cuticular hydrocarbons (CHCs) are found on the outer cuticle of all terrestrial arthropods. Although their primary function is in desiccation prevention, these compounds have also been shown to play a variety of roles in insect chemical communication, from species and sex recognition to providing cues of dominance and attractiveness. However, despite growing evidence of their versatility as cues, our knowledge of how CHCs are used in mating interactions is limited to Drosophila and field crickets. In this thesis I investigate the roles CHCs play in interactions at each stage of the mating process in the broad-horned flour beetle Gnatocerus cornutus. I assess the relative importance of CHCs in influencing male reproductive success and examine the complex interplay between different episodes of selection and the mechanisms of sexual selection acting on males. I use a combination of behavioural assays, experimental manipulations and gas chromatography. First, I identify the role of CHCs as cues of sperm competition risk and intensity, demonstrating how the presence of male-derived CHCs on the cuticles of virgin females elicits males to adjust their pre- and post-copulatory investment (chapter 2), by providing information on the state of their competitive environment. I then go on to look at the stability of CHCs as cues of sperm competition over time, finding that they are highly sensitive to environmental degradation (chapter 3) and do not persist in the habitat substrate of this species. Next, I investigate how male CHCs determine fighting and mating success. By estimating and comparing the strength and form of sexual selection imposed by male-male competition and female mate choice, I show that male CHCs are subject to strong antagonistic sexual selection (chapter 4). By experimentally manipulating male CHC profile, I then attempt to verify the selection gradients estimated for female choice 3 (chapter 5). However, my experimental manipulation fails to verify the importance of male CHCs for female mate choice. Finally, I explore the role of same-sex sexual behaviour (SSB) in determining male reproductive success (chapter 6). I find evidence to suggest that SSB may in fact be a form of aggression in its own right, and demonstrate that SSB and fighting may provide equivalent means for males to overcome female choice and secure a mating advantage. My results indicate that CHCs play key roles as chemical cues throughout the mating process and significantly impact male reproductive success. My thesis reveals the intricate nature of the relationships between mechanisms of sexual selection, alongside highlighting the need to consider both the social and physical environment when investigating the importance of chemical cues. I discuss the implications of these results for the evolution of male CHCs and how my findings can be used to further our knowledge of this field.
Lane, S.M., Solino, J.H., Mitchell, C., Blount, J.D., Okada, K., Hunt, J. and House, C.M., 2015. Rival male chemical cues evoke changes in male pre-and post-copulatory investment in a flour beetle. Behavioral Ecology, 26(4), pp.1021-1029.
PhD in Biological Sciences