School of BioSciences - Theses
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ItemAdaptations for temperature control in bird eggs: the role of reflectance( 2021)Early life stages are highly vulnerable in many animals. In birds, egg temperature must be maintained within an optimal range for successful development and survival. Chilling and especially overheating can lead to abnormal embryos and even be lethal. Bird embryos are effectively ectotherms because heat from incubation by parents is essential for embryo development. Therefore, parental behaviours are crucial for egg temperature regulation during the incubation period. Parents, however, face tradeoffs between incubation and self-maintenance. There are often periods of time when bird parents will leave the nest for foraging or territory defense etc., and eggs will be then left unattended. During this time, egg temperature will not be regulated by parents and will be affected by both extrinsic factors such as environmental conditions (air temperature, solar radiation and humidity) and the architecture of the nest; and intrinsic factors such as eggshell reflectivity and egg size. In this thesis I focused on studying the relationship between these factors and egg thermoregulation. Eggshell reflectivity is one of the most important intrinsic properties that may affect egg temperature. Wisocki et al. (2020) and Gomez et al. (2018) provided evidence that eggs tend to be darker in colder climates and higher latitudes. They suggested that darker colours are adaptive for eggs to retain heat in colder environments for thermoregulation. These studies, however, looked only at ultraviolet-visible wavelengths (300 – 700 nm). These wavelengths correspond to egg colour patterns and may play a role in camouflage, egg recognition, protection from DNA damaging light, in addition to temperature regulation. Due to the multiple potential functions of egg coloration, it can be difficult to isolate the role of specific selective pressures. By contrast, reflectance of near infrared (NIR) wavelengths (700 – 2500 nm) primarily affects temperature. NIR wavelengths account for more than half of the solar energy. In 1978 Bakken et al. (1978) found a uniformly high near infrared reflectance among 25 species (19 of them are ground nesting birds with cryptic eggs) and pointed out the potential importance of NIR reflectance for egg thermoregulation. However, since then there have been no subsequent studies examining the importance of NIR reflectance on bird eggs on a broader scale. In this thesis, I first aimed to study the macro-evolutionary relationships between eggshell reflectivity, climate and nest type in birds. We predicted that eggs would have higher eggshell reflectivity in hot climates, and species with eggs that are exposed would have higher eggshell reflectivity. Using a phylogenetic comparative approach among 186 species of Australian birds we found that eggs tend to have higher total reflectivity in hotter climates with higher solar radiation. Moreover, species with open nests (i.e. with potentially higher exposure to direct sunlight) had higher NIR reflectivity than species with closed nests. This suggests that eggshell reflectivity, especially NIR reflectivity, may play an important role in egg thermoregulation. Second, we investigated how egg size, reflectivity and exposure interact to affect egg temperature. We predicted that high eggshell reflectivity and shade can protect eggs from reaching lethal temperature compared to eggs with low eggshell reflectivity and without shade. We used a biophysical model to predict egg temperatures in a hot environment (Kimberley, Western Australia). The results showed that eggs with higher reflectivity exceeded the critical thermal limit for less time and did not reach temperatures as high as eggs with lower reflectivity. The amount of sunlight eggs are exposed to (shade levels in the model) also strongly affected egg temperature. These results indicate that eggshell reflectivity and exposure to sunlight are likely to be important for egg temperature regulation during incubation, particularly in hot environments. Reflectivity had a greater effect on the temperature reached by large eggs than small eggs, even though small eggs had a higher heating rate. Together, this thesis highlights the importance of eggshell reflectivity on egg thermal control and contributes to our understanding of the macro-evolution of reflectivity in bird eggs.
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ItemSeasonality and community composition of parasitoid wasps of four agromyzid leafminer species (Diptera: Agromyzidae) in Victoria( 2020)The vegetable leafminer, Liriomyza sativae Blanchard (Diptera: Agromyzidae), was first detected in the Torres Straits in 2008, crossed over to the tip of Cape York in 2015 and now poses a threat to Australian crops. This species is an economically important secondary pest in many parts of the world; populations readily evolve resistance to insecticides and benefit from the use of chemical controls against other pests, which kill their natural enemies. Liriomyza sativae is expected to spread into Australia’s agricultural production areas and it is therefore valuable to investigate the local biological agents that could contribute to future integrated pest management (IPM). I assessed the abundance and diversity of the hymenopteran parasitoid wasps of four common agromyzid flies in southern Victoria (Liriomyza brassicae (Riley), Liriomyza chenopodii (Watt), Phytomyza plantaginis Goureau, and Phytomyza syngenesiae (Hardy)) to evaluate their potential as candidates for control of L. sativae. I monitored six sites in Melbourne over a period of 18 months by collecting mined leaves from a range of plant species and rearing adult flies and their parasitoids. Additional sites around Victoria were also sampled to offer a snapshot of the agromyzid presence across the state. Eleven wasp species were identified in total, two of which were only classified to morphospecies level, including known parasitoids of L. sativae overseas and species reared from L. sativae populations from far north Queensland. Ninety percent of the parasitoids were eulophids (Hymenoptera: Eulophidae), with the rest consisting of opiines (Braconidae) and Pteromalinae (Pteromalidae). The adventive Chrysocharis pubicornis (Zetterstedt) was the most abundant parasitoid, reared almost entirely from Phytomyza hosts, followed by an Asecodes sp. and the introduced Diglyphus isaea (Walker). We recorded the first male Ph. plantaginis for Australia. Males were only found at Melbourne locations and these populations tended to have a female-biased sex ratio. Variation in sex ratio may be host plant dependent, as the female:male ratio was 4:1 from the host Plantago lanceolata L. while it was 1:1 in more limited samples from Plantago major L. The four common local agromyzids reached peak abundance at different times of the year and together supported a stable community of both adventive and native parasitoids. Of the species reared, several are known to attack L. sativae including D. isaea, Hemiptarsenus varicornis (Girault) and Neochrysocharis formosa (Westwood). The wasps reared include candidates for augmentative or conservation biological control that should be further considered in the event that L. sativae becomes a widespread pest of Australian crops.
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ItemModeling the Distribution of a Widely Distributed butVulnerable Marsupial: Where and How to Fit Useful Models?( 2020)The greater glider (Petauroides volans) is the largest of the Australian gliding marsupials. Once abundant, it is now nationally listed as vulnerable because evidence of population decline exists across its distributional range. This decline and its likely relation with wildfire and logging, has prompted focus on conservation of this species. Species Distribution Models (SDMs) relate species occurrences to environmental variables at observation sites to predict distributions or make inferences about their key drivers. Conservation planning and land management use SDMs to deliver predictions of species distributions across landscapes. When modelling a broadly distributed species like the greater glider, data are often gathered from sources that vary in quality. In such cases, accounting for sampling biases and selection of geographic extent for model fitting are two key methodological steps that can largely influence models results. In this thesis I tested the effect of taking alternative decisions regarding occurrence data processing, modelling method and geographic extent on models’ predictive performance and how different decisions might (or not) provide different information for conservation and land management actions in a region subject to commercial logging. In the first research chapter, I tested different methods for dealing with sampling biases when modelling the distribution of the greater glider across its entire range. I compiled a dataset of occurrence data of the greater glider and other arboreal marsupials and tested alternative ways to use this large but biased dataset. I used modelling methods that utilize different types of occurrence data, namely, presence-background and presence-absence methods. I found that using presence-absence models fitted to an expanded presence-absence dataset in which some data were inferred provided the best performing models. In the second research chapter, I compared range-wide and local SDMs to predict the distribution of the greater glider in East Gippsland, Victoria. I found that two models: a range-wide one, and a local model fitted with higher quality variables, were the best performing. Models delivered somewhat different spatial predictions but broadly agreed on the largest patches of high predicted probability and gave similar estimates of the proportion of habitat across different land uses in the East Gippsland Regional Forest Agreement. I also completed a preliminary assessment of the extent of greater glider habitat burnt during the 2019-2020 wildfires that affected eastern Australia. I found that a large proportion of habitat was affected, including recently established protected areas. Throughout this thesis I show that decisions regarding data processing, selection of modelling method and geographic extent can lead to substantially different distribution predictions. In a context of local conservation planning such as the East Gippsland Regional Forest Agreement, different models, nevertheless, provided similar information on the implications that forest management and logging restrictions may have on the conservation of greater glider habitat in this region. Although the solutions we implemented relied on the broad availability of biodiversity data in Australia, we advocate for modellers and users to undertake thorough assessments of the data available in their regions and think carefully on how to make the best use of it.