Zoology - Theses

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    Thermal advantages of colour change in bearded dragon lizards, Pogona vitticeps
    SMITH, KATHLEEN ROSE ( 2014)
    Many animals possess the remarkable ability to change colour, and this ability has several potential functions, including communication, social signalling, and camouflage. However, the functional significance and drivers of colour change are still poorly understood in many taxa. In this study, I applied laboratory and field approaches to examine an important, but understudied potential function of colour change in terrestrial ectotherms: thermoregulation. I quantified colour change in response to temperature in wild-caught bearded dragon lizards (Pogona vitticeps), which are known for their marked individual colour change and geographic colour variation. For comparison, I also quantified the extent of non temperature-dependent colour change from dark to light states elicited during social interactions and at different times of the day. I found that lizards showed substantial animal-visible (UV-Vis) and near infrared (NIR) skin reflectance change in response to temperature for dorsal but not ventral body regions. By contrast, lizards showed the greatest capacity for colour change on the ventral body regions under other (non temperature-dependent) circumstances. I then used biophysical models to predict the thermal benefit of colour change to a bearded dragon lizard, and found that in the morning, under environmental conditions characteristic of the field site during the breeding season, the maximum temperature-dependent change in dorsal reflectivity would result in a 9% increase in the rate of heating. Although this temperature-dependent colour change may therefore aid thermoregulation, colour change is likely to be less important as a mechanism for bearded dragons to thermoregulate than other mechanisms such as behavioural changes in posture and shuttling between sun and shade. Therefore, colour change may have primarily evolved to enhance social signalling or camouflage, but subsequently been co-opted for thermoregulation. To further understand the relative importance of the different functions of colour change to a bearded dragon in the wild, and how they accommodate these functions when they conflict, I quantified colour change in 11 free-ranging bearded dragons (Pogona vittceps) over an 8-week period during the breeding season (October 9th– November 28th, 2013). In addition to taking daily snapshots of multiple lizards over the entire field study, I followed a single lizard through an entire day (‘day in the life’), and modelled the effect of different thermoregulatory behaviours on core body temperature. From this, I found that lizards showed a significant and consistent relationship between their dorsal skin coloration and both background coloration and either core body temperature or skin temperature. However, background colour explained the most variation in lizard colour, and there was no evidence that these lizards exhibit temperature-dependent background choice. Furthermore, the focal lizard that was followed through the entire day behaved very similarly to a predicted modelled “thermoregulating” lizard, suggesting that in the wild, behavioural thermoregulation may be more important for regulating body temperature than colour change. Overall, the data presented in this thesis shows that colour change in bearded dragons functions in thermoregulation but that this is likely to be secondary to its use for communication and camouflage. These data contribute significantly to our understanding of the evolutionary drivers of colour change in terrestrial ectotherms.
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    The domestic cat as a model for endangered species: analysis of gamete maturation, cryopreservation and embryo development
    BARNES, SERENA ( 2014)
    The domestic cat represents an accepted model to develop assisted reproductive technologies for non-domestic cat gamete management. Despite technological advances in other animal models, application to the domestic cat has been limited. It is likely that current methods have not been properly optimised for cat gamete management. The purpose of this research is to determine if assisted reproduction can be further optimised for the cat model by investigating and validating modifications to both male and female focused techniques. Specifically, this included research on the abilities of two media systems to support oocyte maturation in the domestic cat, to compare of the abilities of two cryopreservation protocols to support survival of epididymal cat spermatozoa, and to describe the composition of follicular fluid from pre-ovulatory follicles to understand the nutritional requirements of domestic cat oocytes during maturation to improve current formulations of maturation medium and thus potentially generating higher blastocyst development rates from IVM oocytes. Overall, the findings of this thesis highlighted the insufficiencies of current embryo production methods from IVM cat oocytes, likely due to poor maturation conditions as opposed to inadequate embryo culture medium. This necessitated the analysis of metabolites in follicular fluid in order to identify components that can be used to develop a physiologically relevant maturation medium. While both cryopreservation protocols equally supported post-thaw survival of epididymal cat spermatozoa, findings from this thesis suggest a concentration of 8 × 106 mL-1 should be used for fertilisation and metabolic assays of post-thaw epididymal cat spermatozoa, as fertilisation and blastocyst development were not different between chilled and frozen-thawed treatments at this concentration and lower concentrations reduced the quality of post-thaw epididymal cat spermatozoa. Finally, the metabolic profiles of cat reproductive cells and fluids not only highlight the importance of metabolism as a parameter for cell quality in spermatozoa, but also the unique requirements of domestic cat oocytes and embryos.
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    Activity of insectivorous bats at gold mining water bodies: risks associated with consumption of cyanide-bearing waste solutions
    Griffiths, Stephen R. ( 2013)
    Insectivorous bats (microbats) are commonly recorded in large numbers in the airspace above water bodies from dusk to early evening when they emerge from daytime roosts to forage and drink by swooping down to lap at the water’s surface while in flight (i.e. drinking on the wing). Microbats are known to visit and interact with wastewater impoundments at gold mines, which contain cyanide. When cyanide concentrations exceed a critical toxicity threshold significant mortality events can occur in microbats. Despite this evident risk, monitoring of microbats at the majority of gold mines in Australia is either inadequate or non-existent. In this thesis I address the lack of prescriptive methods for monitoring microbat interactions with water bodies at gold mines by firstly investigating the level to which microbats produce echolocation calls associated with drinking. Through the development of a novel monitoring technique, I recorded the first empirical evidence that microbats produce terminal buzz calls while drinking on the wing. These findings indicate that the occurrence of both foraging and drinking buzzes should be considered in the design of future ecological research comparing microbat foraging rates in the airspace above different water bodies. I investigated activity of bats in the airspace above two water bodies at Cowal Gold Mine, western New South Wales, Australia. Microbat activity was highly variable across nights and months, however overall activity was similar at both the cyanidebearing tailings dam and a rainwater-derived farm dam. The regular presence and highly variable activity of microbats in the airspace above water bodies at this gold mine are consistent with the findings of previous studies investigating wildlife cyanide toxicosis risks at gold mines. During this study, tailings slurry and supernatant pooling within the tailings dam were consistently well below the industry protective concentration limit of 50 mg/L weak acid dissociable (WAD) cyanide. Therefore, wastewater solutions stored within this open impoundment posed an extremely low risk of wildlife cyanide toxicosis, including to microbats. Several studies have shown that elevated levels of salinity in mine waste solutions stored in open impoundments prevent wildlife cyanide toxicosis by eliminating drinking and reducing foraging. This appears to be consistent for diurnal wildlife interacting with open impoundments, however the risks to nocturnal wildlife of cyanide exposure are unclear. I investigated the activity of microbats in the airspace above hypersaline cyanide-bearing tailings dams, other saline water bodies and fresh (potable to wildlife) water bodies at two gold mines in the Goldfields of Western Australian: Sunrise Dam Gold Mine (SDGM) and Kanowna Belle Gold Mine (KBGM). Microbats were recorded in the airspace above each water body, but were more active at fresh than saline water bodies. While considerably more terminal echolocation buzz calls were recorded in the airspace above fresh than saline water bodies at both mine sites, it was not possible to determine whether these buzz calls corresponded to foraging or drinking bouts. However, at SDGM no drinking bouts were observed in 33 h of thermal video footage recorded at one hypersaline tailings dam, suggesting that this water is not used for drinking, and is only used in a very limited way for foraging. As there is no information on salinity tolerances of microbats, it is not possible to quantify the concentration range (likely between brackish and saline) where salinity becomes a physiological stressor to microbats, thereby precluding drinking. It could be assumed that microbats would not be able to tolerate salinity in drinking water at concentrations greater than those documented as toxic for saline-adapted Australian terrestrial wildlife. Therefore when managing sites to avoid wildlife mortalities, adopting the precautionary principle, microbats are unlikely to drink hypersaline solutions (≥50,000 mg/L total dissolved solids). At mining operations that produce potable wastewater solutions, the most effective mechanism for preventing cyanide toxicosis to wildlife, including microbats, is reducing the concentration of cyanide in tailings discharged to open impoundments to below 50 mg/L WAD. Capping spigot discharge concentration at this level will result in habitats downstream of the spigot (i.e. fast-flowing tailings streams and ponding supernatant) being consistently well below 50 mg/L WAD cyanide.
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    Effect of vegetation diversity on natural enemy abundance in two agricultural contexts
    Ghosh, Purabi R. ( 2012)
    Vegetation diversity has long been known to enhance natural pest control at both the local and landscape level. However little is known about the characteristics of this vegetation that promote/shelter more natural enemies and suppress pests. The main aim of this thesis was to examine how characteristics of common non-crop vegetation influence the abundance, diversity and association of natural enemies residing in two different agricultural systems (canola fields and vineyards). These crops were chosen to contrast annual and perennial cropping systems. Canola, grown directly after a pasture phase of a field, is Australia’s most important oilseed crop. Pressure on invertebrates may be greater due to level of disturbance; in contrast, vineyards are often surrounded with various types of vegetation which may enhance invertebrate abundance. To explore this aim, the effect of within crop, non-crop vegetation (grass strips within canola crop) on abundance of pests and natural enemies in the crop was examined. Invertebrates were collected across grass-canola transects in two fields planted to canola with unsown grass strips at intervals. Sampling with pitfall traps and vacuum sampling was completed to collect ground dwelling fauna during two sampling periods: post sowing and post emergence of canola seeds. Invertebrates collected were categorized mainly into two groups: pests and natural enemies. Abundant pests in the canola fields were red legged earth mite, Halotydeus destructor; blue oat mites, Penthaleus spp. and lucerne flea, Sminthurus viridis. Natural enemies considered were spiders (Araneae), predatory mites (Acari), predatory beetles (Coleoptera) and parasitoids (Hymenoptera). In general more predators and parasitoids were found in the unmown grasses of grass strips and more pests in mown sections of the grass strips and overall pests were more abundant in the crops than in grass strips. Vegetation types may have different influences on the biota that reside within them. Thus the effectiveness of different vegetation types in promoting conservation biological control was assessed at vineyards with two types of non-crop habitat: adjacent- grass with and without trees. Invertebrates were sampled in the canopy with sticky traps and on the ground with pitfall traps at 40 sites from six different vineyards at Yarra Valley (Victoria) for five consecutive months from bud burst to harvest (October through February). Collected invertebrates were classified as natural enemies and other invertebrates since none of the invertebrates collected are considered as pests in vineyards. The most abundant natural enemies were generalist predators (spiders and predatory beetles Coleoptera: Carabidae and Staphylinidae) and parasitoids (Hymenoptera), lacewings (Neuroptera), hover flies (Diptera: Syrphidae) and other predatory Diptera (Asilidae, Empididae and Tachinidae), predatory thrips (Thysanoptera), predatory Hemiptera, and ladybird beetles (Coleoptera: Coccinellidae). Other invertebrates analyzed included several other beetle families, thrips (Thysanoptera) and several herbivore families of Hemiptera. Overall no effect of vegetation diversity was identified in this study though a significant vineyard effect was revealed for most of the natural enemies and other invertebrates.
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    Plumage pattern function and evolution: a phylogenetic and comparative approach
    GLUCKMAN, THANH-LAN ( 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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    Colour pattern evolution in Australian dragon lizards (Agamidae)
    CHEN, I-PING ( 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.
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    Population assessments of ungulate prey and Komodo dragons across protected areas in eastern Indonesia
    Husen, Achmad Ariefiandy ( 2011)
    Prey species can influence the population dynamics of their predators. Therefore, to conserve and manage endangered or threatened species, it is crucial to understand predator-prey relationships and to monitor the abundance of predators and their prey. The Komodo dragon (Varanus komodoensis) is an apex predator endemic to Indonesia. It is considered a vulnerable species due to demographic decline and a limited distribution. However to date, little monitoring has been conducted to estimate the spatial and temporal variation in the abundances of the Komodo dragon and its ungulate prey species. This study evaluated the usefulness of faecal counts and distance sampling for monitoring the abundance of the three major prey species of Komodo dragons. This study also investigated site occupancy of Komodo dragons, and examined the influence of site-specific covariates (prey abundance, habitat type and level of protection) on site occupancy across 11 sites on five islands in and around Komodo National Park, eastern Indonesia. Faecal densities of three ungulate prey species: Timor deer (Cervus timorensis), feral pig (Sus scrofa) and water buffalo (Bubalus bubalis), were positively correlated with their population densities estimated from distance sampling. The abundance of Timor deer was negatively influenced by the abundance of water buffalo, possibly through competition for space and food. Whilst for feral pig and water buffalo all models give weak support (wi ≤ 0.37) to explain the variation in their abundances. Several competing models were evaluated to estimate their effects on the site occupancy of Komodo dragons. The two most parsimonious models indicated that ungulate prey, representing a deer density model (∆= 0.00; w= 0.68) and an additive model incorporating deer and buffalo density ((∆= 1.61; w= 0.30) were both positively correlated with site occupancy estimates for Komodo dragons and presumably the abundance of Komodo dragons. The site occupancy of Komodo dragons and the abundance of their prey on small islands and Wae Wuul Nature Reserve on Flores Island were lower than on the larger islands within Komodo National Park. This study concluded that faecal counts are more useful than distance sampling for population monitoring of the ungulate prey of komodo dragons, and recommends annual monitoring of ungulates in and around Komodo National Park to be undertaken using faecal counts. This study also recommends that continuous monitoring of Komodo dragon site occupancy and estimation of trends in prey densities should be implemented for detecting spatial and temporal changes across time. The implementation of long term population monitoring would ensure that robust data is available for managers to address population trends. I also propose conservation efforts essential to ensure the persistence of Komodo dragon populations: (i) increasing the level of protection to reduce the risk of deer hunting, (ii) translocating Timor deer to low abundance areas to recover their populations, (iii) excluding domesticated buffalo from Wae Wuul Nature Reserve, and (iv) investing in sustained annual monitoring program for the Komodo dragon and its ungulate prey populations, to be implemented across Komodo dragon distributions, and especially in small islands and the Wae Wuul Nature Reserve.
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    Sensory biology of aquatic Australian crustaceans
    PATULLO, BLAIR ( 2010)
    Sensory biology of animals is studied throughout the world for the insight it provides to understanding ecosystems and improving how we manage species. In this research, I designed experiments to investigate the sensory biology and behaviour of two Australian species of freshwater crayfish from the genus Cherax, the yabby (Cherax destructor) and redclaw crayfish (Cherax quadricarinatus). Experimental apparatus were constructed and tailored to test specific questions on physiology, tactile (touch) sensitivity, observation techniques, aggressive behaviour and responses to electrical fields. The outcomes were: • abdominal muscle mass was positively correlated to the size of the electrical fields produced by swimming crayfish, • behaviour changed in response to contact with different structures and textures of wall surfaces, • computer analysis of underwater behaviour was similar to that scored by a human observer, • the level of aggression in groups of crayfish changed as group size increased, and • two species of crayfish responded to electrical fields in the water by decreasing their locomotory movement. These results reveal a way in which physiology relates to behaviour, how crayfish and other crustaceans may sense the invisible and behave in aquaculture ponds, as well as documenting methodology to further investigate these areas in the future.