School of BioSciences - Theses
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ItemMolecular ecology of Aedes aegypti and Aedes albopictus following Wolbachia releases( 2017)Control strategies involving Wolbachia transinfections have recently been developed for the dengue vectors Aedes aegypti (yellow fever mosquito) and Ae. albopictus (Asian tiger mosquito), and localised field trials have indicated their potential for wide-scale implementation. This thesis uses molecular techniques to investigate ecological aspects of these two species, with an emphasis on their dispersal through anthropogenically-modified environments. I first analysed spatial spread of Wolbachia through Ae. aegypti in Cairns, Australia, following introductions into three non-isolated release zones of variable size and condition. In accordance with predictions, I observed successful establishment and spatial spread at the two release zones of area > 0.5 km², and erratic spatial dynamics at the smaller release zone (0.11 km2). However, reinvasion by uninfected Ae. aegypti threatened the stability of the invasion at the largest release location. Additionally, spread was heterogeneous in extent and slow, indicating possible restrictive effects caused by various potential processes. I performed double-digest RAD-sequencing and Wolbachia quantification assays on a sample of Cairns Ae. aegypti to investigate four potential causes of slow spread: i) barriers to Ae. aegypti dispersal; ii) dispersal distances being leptokurtically distributed; iii) imperfect transmission of Wolbachia from mother to offspring; and iv) spatially heterogeneous host densities. I detected a significant barrier effect of Cairns highways on Ae. aegypti dispersal using distance-based redundancy analysis, and quantified barrier strength using a patch-based simulation analysis. I detected putative full-siblings in a pair of ovitraps > 1.3 km apart, indicating long-distance movement most likely a result of accidental transportation by humans. I also detected a pair of full-siblings in which only one was Wolbachia-infected, indicating maternal transmission failure of Wolbachia in the field. I found no evidence for slow spread caused by heterogeneous host densities. I aimed to corroborate these findings of anthropogenically-influenced dispersal in an urban population of Ae. albopictus from Guangzhou, China, using similar molecular protocols but at a larger spatial scale. Although I found no evidence of dispersal barriers, I detected passive movement along human transportation networks. Specifically, multiple pairs of closely-related individuals were collected from two sampling locations > 3.5 km apart, suggestive of transportation along roads, and mosquitoes sampled further from ports had higher average genetic distances than those nearer to ports, implying higher-than-average gene flow between ports. These results highlight some of the difficulties in designing successful strategies of Wolbachia-based control, while also providing clear evidence for their potential to be implemented globally. My findings are informative for implementing such control methods, as well as designing strategies to prevent or limit biological invasions of either species.
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ItemCoping style and group dynamics in a cooperative breeder, the superb fairy-wren (Malurus cyaneus)( 2016)Group dynamics – the movements and interactions of individuals within and between groups – are known to play an important role in influencing key life history events such as dispersal and reproduction. Nevertheless, there is considerable variation in conspecific interactions and life history strategies that remains poorly understood. Over recent years, a growing number of studies have shown that individual animals consistently differ in their behaviour over time and across contexts. This phenomenon is typically referred to as ‘animal personality’ or ‘temperament’ and evidence is accumulating that these behavioural differences can help to explain the form and expression of life-history traits. However, currently most evidence for a relationship between personality and life-history traits comes from theoretical or captive studies. There is a need to verify these ideas under natural circumstances, to assess the true impact of personality on individual life-histories and fitness. In this thesis I investigated whether and how individual coping style (a narrow-sense proxy of personality) is related to the performance of different tasks during breeding and to individual natal dispersal strategies in a wild population of cooperatively breeding superb fairy-wrens (Malurus cyaneus). In this species, males can disperse at any point in their life and help their parents raise successive broods while still at home, while most females disperse in their first year. By conducting behavioural assays, of fairy-wren behaviours (boldness, exploration, aggression) under controlled conditions, I first established that individual fairy-wrens in my population indeed show distinct coping styles. I then tested whether individual differences in coping style where related to contributions to key tasks within social groups, specifically alloparental care (nestling feeding behaviour), territory defence (responses to simulated conspecific territorial intrusions) and nest defence (responses to a novel object at active nests). To test for relationships between coping style and dispersal outcomes, I experimentally created temporary breeding vacancies by removing male breeders from territories without helpers to prompt dispersal by a male helper from one of the neighbouring territories into the vacant breeding position. Finally, I used data on natural cases of male and female dispersal, collected over six consecutive years of population monitoring to test whether individual dispersal strategies were related to coping style. My findings suggest that coping style has much less influence on group dynamics than suggested by theoretical and captive studies. First, cooperative division of tasks such as offspring provisioning and nest defence did not occur during breeding, nor did individuals consistently differ in the amount of help provided. Coping style did not affect feeding rate or response to a simulated conspecific intruder, and only played a role during inspection of a novel object near the nest when more than one bird was present: birds with relatively fast coping styles (exploratory, active and bold in the artificial environment) responded more strongly to the object than group members with slower coping styles. In general, the social context had the strongest effect on behaviour. Individuals responded much more strongly to the novel object and the simulated conspecific intruder when in the company of other group members than when alone. Second, coping style only played a role in dispersal among young males. Males that dispersed during their first year of life on average had a faster coping style than those that delayed dispersal. Among males that dispersed after their first year, dispersal timing was not related to coping style, but rather to the likelihood of inheriting the natal territory. In females, dispersal timing was not related to coping style, but rather to hatch timing. In superb fairy-wrens the social and physical environment seem to play a larger role than personality in how individuals behave within their group and in the dispersal decisions they make. Task division did not occur and individuals instead seemed to be flexible and responsive to environmental stimuli in relation to offspring care and defence. Investment in cooperation is therefore not a good predictor of life-history strategies in this species. With regard to dispersal strategies, males with faster coping styles indeed disperse or die young, as predicted by the pace-of-life syndrome hypothesis. Due to the reduced variance in coping styles among males that disperse later, variation in dispersal timing among these males is rather due to external factors such as stochasticity of dispersal opportunities and dispersal motivation based on conditions in the natal territory. For females dispersal is a prerequisite for reproduction, which leads to higher dispersal motivation compared to males. The importance of hatch date for dispersal timing indicates that environmental conditions outweigh coping style as a predictor of dispersal strategies. Together, these results show that theoretical and captive studies may overestimate the role of personality in life-history strategies in the wild by oversimplifying the environment. Captive studies may teach us about underlying mechanisms, but only by testing predictions in the field will we truly know their significance in individual life- histories and their consequences for evolution.
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ItemEarly life-history drivers of connectivity in a temperate marine fish metapopulation( 2016)Metapopulations are connected by the movement of individuals between local populations. For marine organisms that are benthic or demersal as adults, this movement occurs entirely in the earliest life stage, as pelagic eggs or hatched larvae, dispersing through the plankton for days to months before settling to a new population. This dispersal phase, and the carry-over effects from dispersal into subsequent life-stages, has fundamental implications for population dynamics and metapopulation persistence, yet for most marine organisms very little is known about what drives dispersal, settlement, and recruitment within individual species. This thesis investigates early life-history drivers of population connectivity in a temperate marine fish metapopulation, by picking apart, and then putting back together, the complex and interacting processes acting on each stage of the early life-history – dispersal, settlement, and survival – of the southern hulafish (Trachinops caudimaculatus). In the dispersal phase, it is well recognized that the environment encountered by dispersing larvae can contribute to differences in the quality of dispersers (disperser phenotype), however, very little is known about how the disperser phenotype directly influences the dispersal process. Findings from CHAPTER TWO show how phenotypic variability influences dispersal outcomes through the influence of disperser phenotype on relative vertical distribution throughout the water column. Using otolith elemental signatures from the dispersal period of recruit T. caudimaculatus collected from 13 populations around Port Phillip Bay (the study system), CHAPTER THREE provides evidence that dispersal pathways are not independent, and explores the implications of shared dispersal histories for patterns of recruitment and population connectivity. At the end of the dispersal period, larvae must locate suitable habitat for settlement, and making the right choice at this transitional stage can be critical for successful recruitment into the population. Through a series of manipulative laboratory and field experiments designed to untangle key extrinsic (habitat-associated) drivers of settlement and survival, findings from CHAPTER FOUR demonstrate a link between sensory information, habitat selection at settlement, and survival in the post-settlement environment, CHAPTER FIVE investigates the implications of these habitat selection decisions at settlement on post-settlement performance, and illustrates how habitat quality and social context can influence shoaling behaviour. The combined results from these studies provide evidence that larval phenotype is a critical factor influencing the likelihood of individual success at every stage of its early life, through direct effects on fitness, and carry-over effects that determine fitness and survival at each subsequent stage. At the metapopulation level, phenotypic variation can indirectly but significantly alter patterns of recruitment and connectivity of local populations. Since the stages across early life history of marine organisms are ecologically linked, this research thesis spanning the early life stages of one temperate reef fish species makes considerable strides towards our understanding of both individual performance in this vulnerable early stage, and how this variation can scale up to influence the dynamics of marine metapopulations.