Zoology - 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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ItemEvolutionary ecology of multiple ornaments in the golden whistler( 2005-12)The function of multiple display signals in golden whistlers (Pachycephala pectoralis) was investigated over three field seasons (2001/02 – 2003/04) at Toolangi State Forest (Victoria, Australia). Male golden whistlers are highly ornamented and possess several elaborate plumage displays, including a yellow breast and a conspicuous white throat patch. In addition, they are highly vociferous and possess large song repertoires. (For complete abstract open document)
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ItemBehavioural ecology of the red-capped robin( 2004-12)In this thesis, I describe aspects of the behavioural ecology of the red-capped robin Petroica goodenovii (Petroicidae), relating to its mating system and breeding biology, based on field research during two breeding seasons (2000/01 and 2001/02) in Terrick Terrick National Park (northern Victoria, Australia). Breeding traits of the red-capped robin were typical of many other Australian passerines and included small clutches, long breeding seasons and multiple broods. A comparative analysis within the Petroicidae (members of which are distributed throughout Australasia) revealed that species endemic to Australia had shorter incubation periods, and species from semi-arid and dry woodlands had comparatively longer incubation periods. Red-capped robin abundances within white cypress-pine woodlands of Terrick Terrick National Park were higher than those of nearby eucalypt woodlands, suggesting such pine woodlands provide high quality habitat for red-capped robins. The study site was saturated with robin breeding territories and few territory vacancies were available at any given time. Nestlings that were relatively heavier were more likely to reach independence and disperse. However, rates of juvenile recruitment into the study population were low. Juveniles may be forced to disperse far from their natal territories to establish breeding territories. (For complete abstract open document)
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ItemSexual selection in cephalopods: multiple mating and sperm competition in dumpling squid (Euprymna tasmanica)( 2013)Sex differences in reproductive investment play a crucial role in sexual conflict. One intriguing aspect is conflict over mating frequency. In this regard, the evolution of female multiple mating (polyandry) has received particular attention, especially in systems where females receive no obvious direct benefits from males, and where mating is costly. Here, theory predicts that polyandrous females can increase their reproductive success by taking advantage of the genetic benefits of mating with multiple males. Cephalopods provide an interesting system for addressing this question because the great majority of species that have been studied mate multiply, with females storing sperm from multiple males, and sperm of many species have remarkable longevities. Mating is also likely to be costly in many species. Using the dumpling squid, Euprymna tasmanica, I examined differences in reproductive success between singly mated (monandrous), multiply mated (to the same male) and polyandrous (mated to two different males) females, controlling for recent male mating history and mating frequency. I found polyandrous females produced eggs faster and had larger hatchlings relative to egg mass than females mated once with a single male. These benefits are likely to outweigh the costs associated with mating and help to explain how multiple mating has evolved (or is maintained) in this group. In order to assess the natural level of multiple paternity and sperm use patterns in E. tasmanica, I developed five novel polymorphic microsatellites for this species, and measured the level of multiple paternity in clutches collected directly from the field, and from a series of clutches laid in the laboratory. All clutches measured had multiple paternity, with 2 – 4 sires per clutch, concordant with levels reported in other cephalopods. Clutches collected from the field had significantly higher levels of multiple paternity than those laid over an extended period in the laboratory, suggesting that females mate between laying bouts in the field. In order to understand sperm precedence patterns in this species I genotyped offspring produced from polyandrous females. Here I found that the last male to mate gains an advantage, siring up to 75 % of eggs at the beginning of the laying period. This level decreases to 54 % by the end of the laying period, suggesting that sperm are stratified within the female sperm storage organ at the beginning of the laying period and are more mixed by the end. Patterns of sperm precedence varied markedly among females and this variation was not correlated to any trait measured including male mass, copulation duration or the genetic relatedness of the mating pairs. The fact that all clutches had multiple sires might indicate that genetic diversity of offspring is an important driver of polyandry in this system. When examining mating behaviour in dumpling squid I found that male E. tasmanica perform more sperm displacement behaviour if the female has recently been mated, showing that they are able to determine the recent mating history of females. I found that sperm can be stored for a large proportion of their lifetime, up to 145 days. The data presented here represent a significant advancement in the knowledge of the evolution of polyandry and sperm use patterns in E. tasmanica and for cephalopods more generally.
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ItemPlumage pattern function and evolution: a phylogenetic and comparative approach( 2011)Visual patterns, such as bars and spots, are common in the animal kingdom. In no other group are patterns so exquisite in their arrangement and coloration than in birds. Although bird plumage patterns appear to be visually diverse there are only four types of patterns, which can be broadly categorized into irregular and regular patterning. That these types of irregular and regular patterning are recursive is intriguing and speaks of an underlying shared mechanism on which selection can act. The prevailing assumption is that patterns predominantly function in camouflage, however evidence suggests that they also function in communication in a small number of birds. In particular it has been suggested that barred plumage patterns could be a signal of individual quality. In visual ecology, communication and camouflage seem to be in conflict with one another – visual signals are often conspicuous whereas camouflage has evolved to provide concealment. These ideas of pattern function need not be incongruous if patterns evolved a) for camouflage first and were subsequently co-opted by sexual selection for communication, and/or b) some patterns, specifically barred plumage, evolved for both camouflage and communication to overcome this functional compromise. To test these alternative ideas of pattern evolution I test whether a) patterns were co-opted for signaling in the model group waterfowl and gamebirds, and b) if the evolution of sexual dimorphism in barred plumage indicate camouflage and ⁄ or signaling functions across the class Aves. Additionally, I investigated whether development poses a constraint on pattern evolution in waterfowl and gamebirds. Tracing the most probable evolutionary pathway of plumage pattern evolution revealed that the ancestral state of plumage was uniform coloration. From uniform coloration, patterns initially evolved to be predominantly monomorphic, and subsequently evolved to be sexually dimorphic. In sexually dimorphic patterns, barred plumage frequently evolved in females and males, suggesting a role for both camouflage and communication. However, dimorphic spotted plumage only evolved in males suggesting it predominantly evolved for communication. Overall, it is likely Plumage pattern function and evolution: a phylogenetic and comparative approach ii that patterns originally evolved for camouflage and were subsequently co-opted for signaling. Focusing on the evolution of barred patterns by comparing their prevalence between the sexes I found a higher frequency of female- rather than male-biased sexual dimorphism, indicating that camouflage is its most common function. But I also found that, compared with other pigmentation patterns, barred plumage is more frequently biased towards males and its expression more frequently restricted to adulthood, suggesting that barred plumage often evolves or is maintained as a sexual communication signal. This illustrates how visual traits can accommodate the apparently incompatible functions of camouflage and communication. Lastly, I studied the recurrence of irregular and regular plumage patterns to explore why there are different kinds of patterns that are broadly recursive. By modeling pattern evolution I derived directionality and show that where species exhibit a single pattern, selection need not be constrained by development. However, instances of irregular and regular patterns in the same species are a result of selection on existing patterns. Together this demonstrates that the evolution of patterns is not difficult and that states of multiple pattern types are a result of selection.
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ItemColour pattern evolution in Australian dragon lizards (Agamidae)( 2011)Many animals communicate using elaborate visual signals such as conspicuous colours and patterns, which are influenced by numerous selective forces. However, the relative influences of natural and sexual selection on types of colour and pattern exhibited and the number and complexity of diverse colour pattern elements remain unclear for most taxa. In this study, I applied phylogenetic comparative approaches to examine the evolution of colour patterns in 69 Australian agamid lizard species, a morphologically and ecologically diverse group that relies primarily on visual communication. I examined colour patterns on nine body regions, which include dorsal, lateral, and ventral areas. I tested for associations with indices reflecting different selective pressures from both visual predators and conspecifics. Indices of natural selection included habitat openness, life style, substrate types, and ecological generalism, and my indices of sexual selection were the degree of sexual dichromatism and body and head size dimorphism (SSD). I found that both carotenoid/pteridine-based yellow-red colours and melanin-based black colour are likely to be used as sexual signals in male agamid lizards, as indicated by their association with two indices of sexual selection, the degree of sexual dichromatism and sexual size dimorphism. The use of both yellow-red and black sexual signals suggests that the costs associated with different colour production mechanisms do not limit the expression of sexual signals. Furthermore, the prevalence of different types of colour on different body regions potentially reflects different signalling strategies in this group. I then examined the evolution of colour pattern complexity in Australian agamid lizards. I developed a novel approach to quantify colour pattern complexity based on the Shannon-Wiener species diversity index. Sex differences in colour pattern complexity and the degree of complexity in males were associated with SSD and sexual dichromatism, respectively. These results suggest that the evolution of colour pattern complexity is driven primarily by sexual selection. Greater colour pattern complexity of males than females suggests that sexual selection has led to signal innovation in males, involving the use of additional and/or novel signal types, rather than elaboration of existing signals, which does not influence complexity. By contrast, I found no strong associations between any ecological factors and colour patterns or with the degree of colour pattern complexity, which suggests that the influence of natural selection on colour pattern evolution in this group is difficult to identify within a broad phylogenetic comparative study.