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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ItemPredicting ectotherm life cycles under a variable climate: physiological diversity of matchstick grasshopper eggs and their ecological and evolutionary implications( 2019)Understanding the processes underlying the phenology and distribution of species is a key problem in ecology. These relationships are important for predicting the responses to species to environmental change. Phenology and distribution are closely linked to climate and weather through the thermal dependence of life cycles. However, for many biodiverse taxa, like insects, we have a poor understanding of the mechanistic links between adaptive traits and how life cycles are adapted to seasonal and variable temperature patterns. Insect life cycles are synchronised with suitable climatic conditions at critical life stages, such as the egg stage. Variation in thermal sensitivity of development and dormancy are two mechanisms by which insects can generate adaptive life cycle phenotypes. Eggs, therefore, present a unique opportunity to link adaptive variation in traits with corresponding variation in life cycles and thermal environments to examine how life cycles are adapted to variable climates. To understand the adaptation of insect life cycles to variable climates, we require a mechanistic understanding of the interactions between adaptive developmental traits of eggs and variation in the thermal environment on adaptations. Our ability to test thermal adaptation in ectotherms is also limited by our ability to efficiently characterise thermal responses. In this thesis, I described how thermocyclers are an efficient means of characterising the thermal response of small ectotherms with enough precision and sample size. I then used the widely distributed, endemic and flightless Australian matchstick grasshopper genera Warramaba (Orthoptera: Morabidae) as a model system to examine the significance of variation in thermal responses at the egg stage for life cycles under a variable climate. I used a mechanistic modelling framework to tease apart developmental and environmental sources of variation in life cycles at the egg stage and simulate their consequences for phenology and distribution in the field. Matchstick grasshoppers showed remarkable diversity in developmental responses to temperature at the egg stage, primarily in the expression of dormancy. I found that diverse Warramaba life cycles are shaped by the interactions between such developmental variation and local environmental temperatures. I demonstrated that we can achieve a mechanistic understanding of life cycle adaptation by considering the evolution of temperature-dependent traits and the evolution of life history within the context of seasonal temperature cycles. Mechanistic models are powerful tools to investigate the sources of life cycle variation and their consequences for insect distribution and phenology. Such frameworks are directly transferrable to other socio-economically important or threatened species to understand how insects are adapted to local climatic conditions and predict responses to a changing climate.
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ItemTesting the decline of the threatened New Holland Mouse (Pseudomys novaehollandiae)( 2019)Delineating the distribution of a threatened species is critical for identifying threats and guiding conservation management. The process is challenging, however, especially when a species is rapidly declining, and so changing its distribution. In this context, species distribution modelling (SDM) often lacks the precision needed to inform fine-scale management decisions, but on-ground surveys to test species’ distributions are time and resource intensive. The dilemma can be mitigated to some extent by careful examination of historical data, and optimal monitoring. The New Holland Mouse (NHM; Pseudomys novaehollandiae) is one of many Australian rodent species to have undergone drastic distributional declines since European invasion. Initially recorded in Victoria in 1970, by 2015 NHMs were thought to occur in only 3 of 12 historically occupied regions. I tested this decline with statistical rigour, using extensive Elliott and camera trapping surveys at >500 sites across Victoria. Combining my survey data with 48 years of others’ efforts, I evaluated the utility of standard Elliott trapping surveys and the efficacy of camera trapping for NHMs. I tested whether NHMs were where we would expect based on state-government threatened fauna SDMs, and whether the species’ purported early-successional fire association explained occurrence or abundance. I confirmed the species’ persistence in 5 of 12 historical regions – including regions where NHMs had not been detected in 5-21 years – and expanded the species’ known distribution in two regions. However, these finds can be attributed to a paucity of prior survey effort and were partnered with greater declines elsewhere. Elliott trapping surveys were often inadequate to provide statistical confidence in the species’ absence; camera trap surveys provide a viable alternative for distribution assessments. Standard state-government SDMs provided limited guidance as to the true distribution of NHMs and SDMs for declining species should be interpreted with caution. Time-since-fire did not explain the species’ occurrence and poorly explains abundance, though in certain locations inappropriate fire regimes are a threatening process. Predator control, habitat management, and careful reintroductions are key priorities for conservation of NHMs in Victoria.