School of BioSciences - Theses
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ItemImpacts of streetlights on sleep in urban birds( 2019)Over the past century, artificial light has dramatically transformed our environment. Light at night is increasing globally, to the extent that in many places, true darkness no longer exists. As the timing of light can influence almost all aspects of biology, the alteration of natural light cycles could pose a severe threat to wildlife. One particularly harmful impact could be the disruption of sleep. In this dissertation, I investigate the impacts of artificial light at night on sleep. Despite the importance and prevalence of sleep across the animal kingdom, sleep is arguably underappreciated in studies of ecology and conservation. After providing a general introduction (Chapter 1), I begin by giving a broad perspective of sleep research, including current methods, opportunities, and the significance of sleep for issues such as artificial light at night (Chapter 2). I then provide a review of the evidence for impacts of artificial light at night, in both humans and wildlife (Chapter 3). Finally, I explore the effects of artificial light at night on two diurnal bird species: pigeons (Columba livia) and black swans (Cygnus atratus). I focus on the effects of one of the most common sources of outdoor lighting: streetlights. Light at night from LED streetlights caused pigeons to have less rapid eye movement (REM) sleep and non-REM sleep, have more fragmented sleep, and sleep less intensely than during darkness (Chapter 4). Some of these effects persisted for more than a day after exposure to light at night. In black swans, light at night in a naturalistic environment reduced night-time rest, which we demonstrate reflects reduced sleep (Chapter 5). This research provides the first direct evidence that exposure to environmentally-realistic artificial light at night can disrupt sleep in birds. One possible strategy for reducing disruption of sleep could be to alter the colour of lighting. To test this idea, I compare the effects of two different lighting colours: white (blue-rich) and amber (blue-reduced) light. Previous research has shown that blue wavelengths of light have the greatest effect on melatonin, a hormone important for sleep regulation. However, contrary to my predictions, amber and white light had very similar effects on sleep in both pigeons (Chapter 4) and swans (Chapter 5). Together, these findings will help councils and other land managers to make more informed decisions about lighting, particularly for areas that might offer important refuges for wildlife.
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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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ItemThe role of web-based chemical communication in the mating and foraging strategies of the orb web spider Argiope keyserlingi( 2017)Chemical communication is critical in shaping the interactions of individual animals, both within and between species. Pheromones (species-specific chemical signals) occur in all species and arguably contribute to more animal interactions than any other mode of communication. Nevertheless, our understanding of the role, nature and expression of chemical signals are mostly informed by studies of insects. This thesis investigates the role and expression of web-based chemical components in the orb web spider Argiope keyserlingi. Given female sexual cannibalism, Argiope males are under strong selection to exhibit mate choice and previous studies suggest that males in this genus fine tune their mating decision using contact pheromones (species-specific chemical signals that benefit both the signaller and the receiver) present on the female’s web. Previous studies suggest that males use these web-based contact pheromones to avoid previously mated females. I predict that these web-based pheromones may also provide males with reliable information about the quality of the female as a reproductive partner. Further, as a sit-and-wait predator, I predict that selection will favour strategies that increase encounters between web and prey, including the use of prey-attracting allomones (inter-specific chemical signals that benefit the signaller but are harmful to the receiver). The expression of chemical signals is ultimately determined by a combination of environmental and genetic effects. There is considerable evidence that diet is the most significant factor shaping pheromone expression. This can lead to considerable intraspecific variation in the signal for opportunistic foragers such as spiders, whose diet is influenced by their choice of web placement. This variation presents specific challenges to the receiver who must recognise and respond appropriately to a range of signals. In Chapter 1, I provide a comprehensive review of the literature and argue that diet-mediated pheromones (and signature mixtures) can enforce signal reliability by providing receivers with reliable information about the identity or quality of the signaller. In the context of mate choice in Argiope spiders, this should allow the male to choose a partner that will maximise his reproductive fitness (for example, by providing the receiver with offspring that have inherited good foraging genes). In Chapter 2, I use chemical analyses (gas-chromatograph flame ionisation detection) of silk extracts to demonstrate that there is considerable variation in the web-based chemical components of female A. keyserlingi. My results suggests that this variation is most likely due to changes in the availability of dietary nitrogen following the introduction of the laboratory diet. The maintenance of mate choice requires variation in the signal, so that the choosy sex can distinguish between signallers. Further, the variation in the signal should reflect reliable information. I suggest that variation in the nitrogen-containing components of the silk provides reliable information to searching males about the quality of the female as a reproductive partner. In Chapter 3 I examine how these web-based components vary on a broader scale between geographically distinct populations, as well as their underlying genetic and environmental influences. I found that nitrogen containing web-based chemicals are the most variable between populations, consistent with the view that arthropod predators are nitrogen limited. Furthermore, I suggest that variation in the nitrogen containing components of silk may provide males with reliable information about the nutritional health and foraging ability of the female. Interestingly, I also found that a single unidentified nitrogen containing silk component (unknown amide 3) and the total amount of all nitrogen containing silk components are strongly correlated with female condition, and may therefore provide males with reliable information about the female as a reproductive partner. In Chapters 2 and 3, I characterise a number of interesting web-based chemical components whose functional roles are also worthy of future studies. Of these components, I was particularly interested in putrescine, which is a nitrogen-containing compound and thus an expensive investment for a nitrogen-limited species. Importantly, putrescine also has a distinctive smell (of rotting matter) and is attractive to certain species of Diptera. In Chapter 4, I use field experiments that manipulated the amount of putrescine on female silk to demonstrate that web-based putrescine increases prey encounters for females and therefore acts as a prey-attracting allomone. Additionally, I found differences in prey capture rates between females collected from different populations, suggesting that there is population-level variation in the web-based foraging strategy of these spiders. Given the cost of putrescine and its role in foraging, I investigate whether web-based putrescine may provide males with a reliable signal of the nutritional health and foraging ability of potential mates in Chapter 5. As mating preference in this species changes with the reproductive experience of the male, I test the preference of males with 1 – 2 or 1 remaining mating opportunity to webs built by females given diets differing in protein content and also where I artificially manipulate the putrescine content of silk. My findings suggest that males with just 1 remaining mating opportunity but not males with 1 – 2 remaining mating opportunities use web-based putrescine to make mating decisions. Surprisingly, female diet did not influence male preference for web-based putrescine. In Chapter 6 (appendix), I discuss how anthropogenic changes to the environment (including but not limited to the nutritional environment) can shape the expression of pheromones in insects, and the consequences this may have for sexual selection. On a broader scale, diet-mediated signals employed in either inter- or intra-specific communication are vulnerable to anthropogenic influences, as changes to the environment can affect nutrient availability. Together, my results suggest that variation in the web-based chemical components of Argiope keyserlingi are driven by the availability of dietary nitrogen, and I argue that this variation will allow males to make accurate mating decisions about the nutritional health and foraging ability of the female. In particular, my research suggests an important role for putrescine in both the foraging and mating strategy of this species. Diet-mediated chemical signals such as these can provide reliable information about the signaller, but are vulnerable to environmental shifts (anthropogenic or otherwise) in nutrient availability.