School of BioSciences - Theses
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ItemThe function of female and male ornaments in the lovely fairy-wren( 2019)Ornaments like plumage colours or complex song are generally regarded as male traits that are shaped by sexual selection. By contrast, the factors that shape female elaborate traits have often been overlooked, though they are expressed in females across many taxa. Understanding how trade-offs and selective pressures shape female ornamentation is crucial for advancing our understanding of trait evolution. In this thesis, I investigate the form and function of female and male plumage colour and song in the Lovely fairy-wren (Malurus amabilis), a tropical species in which females and males are both highly colourful and vocal. This was investigated over three consecutive years and field seasons in Far North Queensland, Australia. My thesis research employed field observations, behavioural experiments, and genetic analysis, to test the adaptive function(s) and mechanisms for the evolution of female and male ornamental traits. I explicitly contrast females and males so that we can address, in the light of the abundant work done on males, how females may or may not differ from males. To provide context for the ornamental traits that are exhibited by this species, I first provide a comprehensive overview of the ecology and breeding biology of the Lovely fairy-wren, since a detailed description on the species natural history prior to this work was lacking. To understand the function of plumage colouration, I studied whether plumage colour in females and males is a signal and experimentally tested if it functions in a competitive context. Additionally, I assessed whether plumage colour is sexually selected, by examining its signalling content, costs (survival), and its relationship with reproductive and paternity success. Lastly, I investigated the song function, by describing female and male song structure and examining sex-specific variation in song rate across different contexts. I also used experimental data to examine female and male responses to simulated territorial intrusion. Overall this thesis provides insight into the form and function of both female and male plumage colours and song. First, it shows that visual and acoustic ornaments are important signalling components in different contexts, suggesting that female ornaments are not just a correlated genetic by-product of traits in males, and that selection favours female (and male) expression of traits. Second, the information conveyed by plumage colouration seems to be context-dependent in relation to the sex of the bearer: in males, it may follow the classical pattern of sexual selection, functioning in mate choice and male-male competition, while in females, plumage colours do not seem to be influenced by male choice, but function in same-sex competitive contexts. Third, it highlights that song has convergent functions in both sexes, as females and males have similar song structure and used song year-round in identical contexts for within-pair communication and joint territorial defence. The fact that females and males sing and have bright colours year-round in parallel with their territorial and breeding behaviour, suggests that individuals use their traits to maintain (sexual and non-sexual) resources. This work highlights the importance of studying and considering the fundamental differences in females and males, a necessary step for a realistic understanding of ornament expression, and contributes to the ongoing discussion on the evolution of elaborate female signal traits.
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ItemEvolution of cooperative behaviour in Australian lycaenid butterflies and ants( 2017)Mutualistic associations between butterflies of the family Lycaenidae and ants are common, and the costs and benefits for both partners have been clearly documented. Ant colonies and territories are well defended against intruders of all kinds, thereby providing an ‘enemy-free’ space for the vulnerable caterpillars. In return, tending ants receive a nutritious droplet of food secretions, released by the Dorsal Nectary Organ (DNO). Optimizing ant attendance may be achieved by tailoring the composition and quantity of food rewards to the needs and feeding preferences of the ant colony. Although DNO secretions play a central role in the exchange of benefits within lycaenid-ant mutualisms, cooperation also requires some degree of communication. A critical, unresolved issue in this mutualistic association is how these partners communicate, and in particular how the butterfly larvae are initially accepted by the tending ants. Nestmate recognition in ants is mediated through chemical-based signals, cuticular hydrocarbons (CHCs), and CHC resemblance with the host ant facilitates ant-association across a variety of taxa. Therefore, CHCs are assumed to play a central role in associations of lycaenid butterflies and ants. My thesis research explores the nature of the DNO secretions in three species of the Australian lycaenid genus Jalmenus, J. evagoras, J. icilius and J. ictinus, by investigating the chemical composition of the food rewards and the macronutrient preferences of the workers of ants associated with J. evagoras and J.ictinus. I further investigate how Jalmenus larvae establish ant attendance by examining the CHC composition of J. evagoras larvae and the associated Iridomyrmex mayri ants across a broad and fine geographic scale, and explore the nature and potential resemblance of CHCs between both partners. All three species of Jalmenus provide large quantities of carbohydrates in their DNO secretions, and the tending Iridomyrmex ants show a strong preference for sugar over all single amino acids and amines, except histidine, highlighting a strong concordance between the abundance of different macronutrients synthesised by lycaenid butterfly larvae and the preference of their attendant ants. However, Iridomyrmex ants prefer amino acids other than the most abundant in the larval DNO secretions, suggesting that the larvae may optimise the costs and benefits of amino acid production. Remarkably, lycaenid DNO secretions contain an astonishing number of compounds, some of which may be key nutrients and thus play a significant role in lycaenid-ant associations. This thesis reveals significant and unexpected compositional differences of CHCs between I. mayri colonies. Remarkably, host tree-specific CHC profiles are also found in the associated butterfly J. evagoras. Although resemblance of the overall CHC composition between the two partners was not detected, the great variation of CHC profiles suggests that CHCs serve a function other than purely physiological, possibly as communication signals. This is supported by my findings that workers of I. mayri react significantly less aggressively towards the extracts of larvae that had been tended by nestmate workers compared with larvae that had been tended by non-nestmates. These data are consistent with the variation in cuticular compounds: ants and larvae from the same host tree generally share a number of cuticular compounds that distinguish them from that of other trees. However, host colony-specific compounds may be acquired by J. evagoras larvae through contact with the I. mayri colony. My field experiments show that ant attendance clearly modifies the cuticular blend of J. evagoras larvae, but this was not the simple addition of ‘new’ compounds. When presented with a living early instar larvae, unlike extracts, the frequency of ant aggression was negligible, suggesting that workers of I. mayri use cues other than or in addition to cuticular compounds to recognise lycaenid caterpillars as mutualistic partners. Overall, the findings of this thesis offer new insights into the evolution of cooperative behaviour in lycaenid-ant associations, and provide a valuable addition to the current state of knowledge on chemically-mediated signalling in a mutualistic system.