School of BioSciences - Theses
Permanent URI for this collection
Search Results
1 - 10 of 35
-
ItemLocation-specific cuticular hydrocarbon signals in social insects( 2016)Cuticular hydrocarbons (CHCs) are the most important chemical signals in ants, and convey several vitally important social signals. The exact mechanism of how different signals can be conveyed and perceived simultaneously is largely unknown. The common procedure for studying the chemistry of these signals usually involves extracting the CHCs from the whole insect, which may confound the results by mixing several signals that co-exist on the ant cuticle. To address this problem, this thesis takes a novel approach by distinguishing the CHCs on different body parts of Australian meat ants Iridomyrmex purpureus using chemical analysis and behaviour assays. I revealed the CHC profiles of both workers and alates varied between different body parts, and workers paid more attention to the antennae of non-nestmate and to the legs of nestmate workers. Workers responded less aggressively to non-nestmate workers if the CHCs on the antennae of their opponents were removed with a solvent. These data indicate that CHCs located on the antennae reveal nestmate identity and, remarkably, that antennae both convey and receive social signals. My approach and findings could be valuably applied to chemical signalling in other behavioural contexts, and provide insights that were otherwise obscured by including chemicals that either have no signal function or may be used in other contexts. Workers adjust their behaviour according to their interactions with other workers, who reveal their task assignment through CHC signals. I analysed the CHC profile on the antennae, legs and abdomens of workers, and showed that the leg profile is the best indicator of task identification. Behavioural assays confirmed this finding: workers typically reacted differently to non-nestmate workers engaged in different tasks, but not if the CHCs on the legs of their opponents were removed by washing with a solvent. Lasso and Elastic-Net Regularized Generalized Linear Modelling (GLMNET) revealed which CHC components contribute the most in task and nestmate recognition, indicating that social insects can simultaneously convey functionally different CHC signals on different body parts, thereby allowing more efficient signalling and signal perception. I further examine the taxonomic generality of body-part specific CHC profiles to convey different signals. I compared the body-part CHC profile of seven Australian ants from seven different ant subfamilies, reporting the type, relative concentration and numbers of the CHCs for each species. I found body-part specific CHC profiles in all species, with the variation between species greater than that between colonies of the same species. There is a correlation between the difference of the CHC profile between different body parts and the social complexity of each species, but not with the age of each species. These data indicate that body-part specific CHCs are conserved in phylogenetically different clades of ants, and suggest that this pattern very likely reflects a general and precise mechanism of conveying different social signals in social insects. Finally, I describe the changes, over a 36 hour period, in the CHC profile of workers of I. purpureus, and the behavioural response of their opponents, following removal of the antennal CHCs and experimental manipulation of their grooming behaviour. I found that workers of I. purpureus constantly groom their antennae, regardless of their social encounters, and the behavioural assays and chemical analysis showed that grooming recovers the removed nestmate recognition signals on the antennae. I also noticed CHCs can change over time without grooming behaviour, indicating factors other than grooming can influence the CHC profile on antennae. This study demonstrates the importance of grooming in forming nestmate recognition signals, and explains how different CHC profiles are maintained on different body parts.
-
ItemThe function and evolution of colour polymorphism in the tawny dragon lizard( 2016)Colour polymorphic species are model systems to investigate the evolutionary processes that maintain intraspecific diversity within a population. Colour polymorphism occurs when two or more discrete, genetically inherited colour forms coexist within an interbreeding population. Almost ubiquitously, colour morphs differ in morphological, behavioural, ecological, life history and/or physiological traits in addition to colour that often form alternative strategies. Each strategy has optimal trait combinations that allow morphs to maximise fitness. Variation in the trait composition of morph-specific strategies has important implications for understanding life-history trade-offs and the maintenance of polymorphism within populations. Differences in morph composition and correlated traits between populations can also promote divergence and ultimately speciation. In this thesis, I investigate the evolutionary maintenance of colour polymorphism in the tawny dragon lizard, Ctenophorus decresii. I do so in two distinct ways; by assessing colour vision differences between genetically and geographically distinct monomorphic and polymorphic lineages, and by comparing a range of traits that could differentially affect the fitness of morphs within a colour polymorphic population. In the south of their range, male tawny dragons are monomorphic for throat coloration whereas in the north of their range, they are polymorphic. There are four discrete male colour morphs in polymorphic populations that vary in the presence/absence of yellow and orange coloration; the yellow morph, orange morph, grey morph and orange-yellow morph (a yellow background with a central orange patch). Throat colour is heritable, fixed for life, and is an important sexual signal. Males of the monomorphic southern lineage express ultraviolet (UV)-blue throat coloration, unlike males of the polymorphic northern lineage. Lineages meet at a narrow contact zone where genotypic admixture suggests potential barriers to gene flow and incipient speciation. I determined the cone photoreceptor spectral sensitivities using microspectrophotometry and opsin expression of the two lineages, to see if they differ, particularly in sensitivity to UV-blue wavelengths. I confirmed the presence of four single cone classes in both lineages and provide the first evidence of UV visual sensitivity in agamid lizards. However, whether the lineages differ in UV-blue sensitivity remains unresolved. Within a polymorphic northern population, I assessed a combination of traits associated with each colour morph. I found morph-specific alternative strategies differentiated by consistencies in behaviour and hormones. The orange morph has an aggressive strategy with high levels of androgens while the grey morph has a cautious strategy with low levels of baseline androgens. The yellow morph has a conditional strategy where its aggression depends on the colour of the intruder and exhibits a stress-induced androgen increase. The orange-yellow morph similarly shows aggression conditional on the colour of the intruder but it is the boldest with high levels of androgens. Morphs did not differ in performance (bite force) or space use, and there was no relationship between spatial arrangement and relatedness. However, genetic structure based on microsatellite markers indicated weak genetic differentiation between morphs. Therefore, there are minimal barriers to gene flow between morphs. Instead, frequency-dependent selection is likely to be maintaining polymorphism in the tawny dragon lizard.
-
ItemEndocrine regulation of maternal vascular adaptations to pregnancy( 2016)Pregnancy is a unique physiological condition, with profound renal and systemic vasodilation epitomising maternal cardiovascular adaptations. These adaptations include increases in cardiac output and blood volume, with reduced systemic vascular resistance, underpinned by changes in endothelial and smooth muscle function. Failure of the maternal vascular system to fully adapt to pregnancy gives rise to the serious disease known as pre-eclampsia. Characterised by hypertension and widespread maternal systemic vascular dysfunction, pre-eclampsia affects approximately 5% of pregnancies worldwide and is a leading cause of maternal and fetal death. The pregnancy hormone relaxin contributes to the regulation of the maternal renal vasculature during pregnancy and has recently gained attention as a new vasoactive molecule, largely due to its potential therapeutic effects in heart failure and diabetes. Therefore, the overall aim of my thesis was to examine the role of endogenous relaxin in mediating pregnancy-associated vascular changes more broadly and to investigate whether or not relaxin could be a potential therapeutic to treat the vascular dysfunction characteristic of pre-eclampsia. In women, relaxin concentrations peak by the end of the first trimester when many crucial vascular adaptations occur, including increased uterine angiogenesis. Exogenous relaxin treatment of non-human primates increases endometrial thickness and vascularisation. However, the role of endogenous relaxin in early pregnancy has not been investigated. Therefore, Chapter 2 investigated the effects of relaxin deficiency on endometrial angiogenesis prior to implantation in relaxin gene knockout mice. Overall, the data demonstrated that despite accelerated uterine angiogenesis-related gene expression in relaxin-deficient mice, there was no impact on endometrial angiogenesis. However, there was an increase in progesterone receptor expression so I concluded that increased sensitivity to progesterone is likely to compensate for the lack of relaxin and regulate angiogenesis in pregnant relaxin-deficient mice. In Chapters 3 and 4, I focused my investigation on late pregnancy, a time when circulating relaxin levels are highest in rodents. I chose to investigate the effects of relaxin deficiency on the pregnancy-associated changes to vascular reactivity in resistance vessels, other than the renal vasculature, in mice. In wildtype mice there was a diminished response of the mesenteric artery to angiotensin II. This did not occur in relaxin-deficient mice but could be induced with five days continuous relaxin treatment. Relaxin’s ability to attenuate responses of the mesenteric artery to angiotensin II was independent of the endothelium, and likely associated with an increased contribution of the vasodilator prostacyclin. As our relaxin-deficient mice are not animal models of pre-eclampsia, in the second half of Chapter 4 I took a different approach to test the hypothesis that relaxin could protect the maternal vasculature from developing endothelial dysfunction associated with pre-eclampsia. Relaxin is capable of protecting the aorta from endothelial dysfunction ex vivo. Therefore, I assessed relaxin’s ability to protect the mesenteric arteries from developing endothelial dysfunction ex vivo by incubating them in trophoblast conditioned media containing high levels of the circulating anti-angiogenic factors sFlt-1/sEng for 24 hours. Interestingly, co-treatment of vessels with relaxin prevented the development of endothelial dysfunction that occurred after incubation in the trophoblast media alone. The recombinant form of human relaxin is costly and difficult to synthesise. Therefore, a relaxin mimetic, known as B7-33, was synthesised to overcome these problems. B7-33 successfully binds to the relaxin receptor (RXFP1), with equivalent efficacy to relaxin in several functional assays. While promising as a more affordable alternative to relaxin, no assessment of the vascular effects of B7-33, relative to relaxin, has been completed. Therefore, I designed Chapter 5 to investigate whether or not B7-33 would replicate relaxin’s acute effects on key vascular beds, including the mesenteric artery, small renal artery and abdominal aorta. B7-33 and relaxin selectively enhanced bradykinin-mediated endothelium-dependent relaxation in the mesenteric artery by increasing endothelium-derived hyperpolarisation, but had no effects on relaxation in the small renal artery or aorta. Ex vivo B7-33 also protected the mesenteric artery of mice against sFlt-1 and sEng-induced endothelial dysfunction. I concluded that B7-33 is likely to replicate relaxin’s beneficial vascular actions after acute exposure. Overall, my data suggest that endogenous relaxin plays a minimal role in uterine angiogenesis prior to implantation in mice. However, relaxin plays an important role in mediating vascular adaptations of the mesenteric artery to pregnancy. Exogenous relaxin treatment protected the vasculature of mice from developing endothelial dysfunction characteristic of pre-eclampsia. These data suggest that relaxin is a potential therapeutic to alleviate the maternal systemic vascular dysfunction associated with pre-eclampsia.
-
ItemResolving the evolutionary history of the Australian grass trees, Xanthorrhoea (Xanthorrhoeaceae), using multiple high-throughput sequencing techniques( 2016)Xanthorrhoea (Xanthorrhoeaceae subfamily Xanthorrhoeoideae) is an iconic component of the Australian flora, occurring in heathlands, woodlands and dry sclerophyll forests in eastern and south-western Australia. The last revision of the genus in 1986 recognised 28 species and five segregate subspecies. However, Xanthorrhoea taxonomy can be challenging due to limited variation in vegetative morphology; identification relies primarily on continuous characters which vary within and between species. Geographical information is often heavily relied upon for identifications, yet some species have overlapping distributions. A comprehensive molecular phylogeny incorporating all currently described species and infraspecific variants is required to understand relationships between species, biogeographical patterns, and to resolve taxonomic issues in Xanthorrhoea. High throughput sequencing is significantly changing the way plant systematics research is done; the sheer volume of genetic data obtainable at a low cost per base pair allows for greater sample numbers and more thorough investigation of evolutionary relationships. In this thesis, I use multiple high-throughput sequencing methods to generate nuclear and plastid datasets for resolving evolutionary relationships in Xanthorrhoea. Targeted amplicon sequencing was performed on over 150 samples of Xanthorrhoea for eight plastid loci, forming a detailed phylogeographic investigation of a widespread genus across the Australian mesic zone. Three distinct haplotype groups were identified: one mostly in Western Australia; one in south eastern Australia; and one in north eastern Australia. The divergence between eastern and western populations is suggested to be caused by vicariance events associated with the formation of the arid zone. The approximate geographic location of the genetic border between north eastern and south eastern Australian haplotype groups is near the Southern Transition Zone in eastern New South Wales, which has been identified as a region of genetic distinction in several plant and animal lineages. Several Queensland samples had haplotype sequence related to Western Australian samples, which is likely caused by failure of widespread ancestral plastid variation to coalesce within a species or geographical region. Targeted amplicon sequencing of four low copy nuclear genes displayed the feasibility of this method for separating allelic variants in heterozygous samples. Phylogenies based on alignments of the individual phased loci (i.e., including all allelic variants for an individual) indicated incomplete lineage sorting, with allelic variation within species, widespread sharing of alleles between species, and a lack of geographic structure. However, phylogenetic analysis methods that utilised both the allelic variation within a locus and combined data from all four loci resolved phylogenies showing some taxonomic and geographic structure. Analysis of unphased loci (i.e., alleles within an individual not distinguished) showed a complete lack of resolution, with most of the species resolved as a polytomy. While a fully resolved phylogeny of Xanthorrhoea was not obtained, results from this study show the value of considering the allelic variation of nuclear loci, and indicate that incomplete lineage sorting is a major factor affecting accurate resolution of a phylogeny for the genus. Restriction associated DNA sequencing, (RADseq) is a powerful method for obtaining thousands of loci from throughout the genome of an organism. A modified double-digest RADseq method was used to explore relationships among the Western Australian species. Three clades of WA taxa were identified, and relationships between taxa were well-resolved, except for X. preissii and X. brunonis; these two species together formed a well-supported clade, but genetic variation within the clade did not correlate with current species limits as defined by morphological characters. Scanning electron microscope images of leaf micromorphology indicated some morphological variation useful to distinguish clades and some species. The phrase name entity X. sp. Lesueur was supported as a distinct genetic lineage worthy of recognition, and will be published as Xanthorrhoea lateritica1. A PCR based reduced representation library method, using random primer sequence to amplify multiple loci from the genome was developed to resolve the phylogeny of Xanthorrhoea. Over 3000 loci were sequenced and used to resolve the phylogeny of Xanthorrhoea. Rogue samples that occupy multiple positions within a set of bootstrap trees caused a significant reduction in phylogenetic resolution. Removing rogue samples increased phylogenetic resolution, identified seven clades of taxa, and clarified relationships among species. Rogue samples were not related to sequencing or locus filtering issues, and may be due to incomplete lineage sorting or hybridisation. Three clades of eastern Australian species were identified; these clades were supported by leaf surface micromorphology and geography. In all datasets, determining genetic relationships between species or geographical regions was difficult in Xanthorrhoea: this is attributed to evolutionary factors such as incomplete lineage sorting and hybridisation, or low sequence variation, as opposed to methodological issues. Explanations for the effect of these factors in Xanthorrhoea were related to life history traits, including a long generation time, fire stimulated flowering, large population sizes, and recent speciation events associated with environmental changes during the Quaternary. Several taxonomic issues arising from the results of this research are discussed, including taxa requiring new circumscriptions or reappraisal.
-
ItemThe vasoprotective properties of relaxin in the peripheral vasculature of males( 2016)As our population continues to age, cardiovascular disease is becoming increasingly prevalent and is the primary cause of morbidity and death in Western Society. Vascular dysfunction is a hallmark of cardiovascular disease. Research into potential therapeutics with vasoprotective properties is a current priority in order to reduce the burden of cardiovascular disease in society. The peptide hormone relaxin is recognised for its connective tissue remodelling actions in the reproductive tract during pregnancy and parturition, but it also has vascular actions independent of pregnancy. Relaxin treatment in male and non-pregnant female rodents enhances vasodilation and passive arterial compliance in the renal vasculature. These vasoprotective actions of relaxin may be beneficial in reducing vascular dysfunction and the changes associated with vascular ageing and disease, with the added potential to prolong vascular health in our ageing population. The overall aim of my thesis was to investigate if relaxin (both exogenous and endogenous) protects against the development of vascular stiffness and increased tone, both of which occur with ageing and disease. The vascular effects of relaxin are region-specific, and are thought to occur via relaxin-family peptide receptor 1 (RXFP1). No studies to date have examined RXFP1 expression in different vessel beds or veins. Chapter 3 of this thesis describes the characterisation of RXFP1 expression throughout the vasculature using immunohistochemistry to better understand the vascular targets of relaxin. RXFP1 was localised in both the endothelium and vascular smooth muscle cells in a variety of conduit and resistance-sized arteries and veins. These data provided new evidence of the potential widespread vascular effects of relaxin. I confirmed this in further experiments in Chapter 3 and demonstrated that subcutaneous relaxin infusion (5 days) targeted the mesenteric arteries, promoting geometric remodelling to reduce passive wall stiffness and enhancing nitric oxide bioavailability to increase bradykinin-mediated relaxation. However, relaxin had no effects in mesenteric veins and the femoral circulation. I concluded that in healthy rats, mesenteric arteries exhibit the greatest functional response to exogenous relaxin, and therefore used this vessel bed for much of the remainder of my thesis. The studies from Chapter 3, and the majority of the literature to date examined the effects of prolonged (> 3 days) subcutaneous relaxin treatment. However, clinical trials in acute heart failure patients use only 48 hours of intravenous relaxin treatment. To understand if and how this relatively short duration of relaxin treatment might improve vascular function, in Chapter 4 I assessed the effects of continuous intravenous relaxin infusion on myogenic reactivity, agonist-induced vasoconstriction and passive mechanical wall properties in mesenteric arteries. I also explored potential underlying mechanisms of relaxin action through a screening approach using a multi-gene quantitative polymerase chain reaction array. This short-term intravenous infusion of relaxin had no effect on passive mechanical wall properties or myogenic tone, although it enhanced the underlying contribution of nitric oxide to myogenic tone. My qPCR analysis also identified some novel components of vasodilator and vasoconstrictor pathways that were modulated by relaxin. In Chapter 5, I moved to an animal model of disease because I argued in my previous chapter that investigating the effects of relaxin in healthy animals was not conducive to understanding how it might be a therapeutic in cardiovascular disease. I used spontaneously hypertensive rats to determine whether or not relaxin treatment was capable of reducing the vascular dysfunction and arterial stiffness that are characteristic in these rats. Surprisingly, I found that subcutaneous relaxin treatment for 10 days in the control rats, which were a different strain than those used in Chapter 3 (Wistar-Kyoto rats) had no effect on vascular remodelling or myogenic tone. In contrast, relaxin reversed inward remodelling to reduce circumferential arterial stiffness in spontaneously hypertensive rats although it did not alter myogenic tone. Chapters 3 – 5 investigated the vascular effects of exogenous relaxin, whereas the final study in my thesis investigated the potential vasoprotective effects of endogenous relaxin. Chapter 6 used relaxin gene knockout mice to determine if endogenous relaxin has a vasoprotective role to minimise vascular wall stiffness, and maintain passive compliance and arterial lengthening of mesenteric and femoral arteries in male mice as they age. I first characterised the effects of ageing on the passive mechanical wall properties of mesenteric and femoral arteries in both wild-type and relaxin gene knockout mice, and found that mesenteric arteries stiffened circumferentially with aging, whereas femoral arteries stiffened longitudinally. Surprisingly relaxin deficiency did not exacerbate vasculature stiffening, suggesting that a lack of endogenous relaxin has a minor consequence on vascular aging. Overall, my findings suggest that relaxin has a minimal role in modulating myogenic tone and passive mechanical wall properties of the mesenteric artery, particularly in healthy animals, and that endogenous relaxin does not protect the vasculature against ageing. However, numerous studies to date have demonstrated relaxin’s ability to reduce vascular stiffness in cardiovascular disease and enhance vasodilation, but this is mostly only agonist-induced vasodilation. These studies are referred to in depth throughout this thesis. My thesis also highlighted variable vascular responses to relaxin in different rat strains, and showed that longer durations of relaxin treatment in diseased animals appear to be more effective. The mechanisms of relaxin’s actions (when present) on passive mechanical wall properties in the mesenteric artery remain largely undefined in both healthy and disease models, but most likely occur through activation of RXFP1 receptors localised within the vessel wall.
-
ItemBiodiversity, distribution and evolution of endolithic microorganisms in coral skeletons( 2016)Prokaryotic and eukaryotic microbes regulate key processes in reef ecosystems but very little is known about the biodiversity of microorganisms living inside coral skeletons (i.e. endolithic). Endolithic microalgae, for example, are among the main contributors of reef bioerosion and can facilitate coral survival during bleaching events, but their phylogenetic diversity, distribution and evolutionary origins are largely unknown. We developed a high-throughput sequencing procedure to assess the biodiversity of prokaryotic and eukaryotic microbes in coral skeletons. A surprisingly high biodiversity of green algae was found, including entirely new lineages that are distantly related to known genera. This technique was then applied to study the relative effects of niche specialisation and neutral processes on the spatial distribution of endolithic communities. The results indicated that stochastic processes and dispersal limitation create a high rate of bacterial species turnover within colonies, while niche specialisation explains most of the distribution of endolithic microbes at larger spatial scales. Finally, we studied whether signatures of an endolithic lifestyle could be observed in the chloroplast genome of a common endolithic alga. The results suggested that chloroplast genome streamlining and slow rates of molecular evolution are associated with the low light inherent of endolithic lifestyles.
-
ItemMolecular control of embryonic diapause in the tammar wallaby( 2016)The marsupial tammar wallaby has the longest period of embryonic diapause of any mammal, up to 11 months, during which there is no cell division or blastocyst growth. Since the blastocyst in diapause is surrounded by acellular coats, the signals that maintain or terminate diapause involve factors which reside in uterine secretions. The molecular communication that occurs between the endometrium and the embryo is essential to control the events of embryonic diapause downstream of the uterine endocrine signals. However, it is still unclear how factors secreted from the endometrium affect the blastocyst to control embryonic diapause. Entry into diapause may be caused by a decrease in secretory growth factors and their receptors from or within the endometrium, while their increase may induce reactivation by removal of cell cycle inhibition in the endometrium. In addition, it is known that metabolic quiescence occurs during diapause, for an extended period when the uterus itself is quiescent. It is possible that the embryo survives on factors secreted by the endometrium during this period. This study aimed to profile and quantitate the essential factors in both the endometrium and the uterine flushing, to further our understanding of the molecular control of embryonic diapause. In this study, uterine flushings (UF) and endometrium were used to assess changes in uterine secretions of tammars using liquid chromatography-mass spectrometry (LC-MS/MS) during diapause (day 0 & 3) and reactivation days 4, 5, 6, 8, 9, 11 and 24 after removal of pouch young (RPY), which initiates embryonic development. This study supports earlier suggestions that the presence of specific factors stimulate reactivation, early embryonic growth and cell proliferation. Mitogen related proteins like hepatoma-derived growth factor(HDGF), soluble epidermal growth factor receptors (sEDGFR) and few others regulated by progesterone and oestrogen were present after d3 concomitant with the start of blastocyst mitoses at d4. Proteins involved in p53(tumour protein p53)/CDKN1A (Cyclin dependent kinase inhibitor 1 or p21) cell cycle inhibition pathway were observed in the uterine flushings and endometrium from animals in diapause. We propose that once the p21 inhibition of the cell cycle is lost, growth factors including HDGF and EGFR are responsible for reactivation of the diapausing blastocyst via the uterine secretions.
-
ItemThe behavioural resistance and response of Atlantic salmon to the ectoparasite Lepeophtheirus salmonis( 2016)Behavioural responses of hosts to parasites or risk of infection can drive the success of parasites. Behaviour is a form of resistance or defence that is prevalent in many host-parasite systems, and can occur over fine- or broad-scales. With the meteoric rise of aquaculture and the associated proliferation of parasites with intensive farming systems, the behaviour of the fish being farmed has not been investigated in relation to infection avoidance. Epidemics and outbreaks of parasites are prevalent in every aquaculture system, and behaviour could be harnessed in concert with current methods to prevent and control parasites. But this requires a systematic understanding of the behaviours of the host, their capacity for resistance, and their interaction with the environment and the parasite. This thesis aims to provide knowledge on how host behaviour changes in response to a parasite, in an aquaculture context. I use the model system of Atlantic salmon (Salmo salar) and the ectoparasitic salmon louse, Lepeophtheirus salmonis, which is a heavily researched host-parasite interaction whereby extensive information on both the host and parasite is available. However, even with the global focus on these species, anti-parasite behaviour has not been a primary objective. Over 4 data chapters, I characterise the behaviour and performance of salmon after lice infestation, and describe fine-scale behaviours of the host at the point of infestation. I also compare the behaviour and susceptibility of wild and farmed salmon to lice, to describe the effect of domestication the host-parasite relationship. In these studies, I found that there is a cost of infestation on the swimming performance of salmon carrying high lice loads. Salmon with infestations also changed their depth preferences in sea cages, whereby individuals with higher lice loads swam deeper in the cage, which would have reduced exposure to new infestation. In the tank environment, I also describe the suite of behaviours that confer protection against successful louse attachment, and further showed that these behavioural profiles were slightly different among wild and farmed salmon. Coupled with their behaviour, susceptibility to infestation was higher in farmed strains compared to two types of wild strains. Yet over time, farmed strains had a greater loss of lice compared to the retention rate in wild individuals. This has implications for management and prevention of infections in farmed salmon, and the survival and fitness of wild salmon populations. By providing basic understanding of the ability of salmon to prevent infestation, I found that Atlantic salmon have a fine-scale behaviour defence against salmon lice. The cost of infestation can be high as their swimming performance suffers with high lice loads. With the potential drive to prevent further infestation, they exhibited avoidance of the parasite-risky surface waters in sea cages when carrying a high lice load. While their behaviours can deter successful parasite attachment, farmed salmon are more susceptible to infestation when compared directly to wild salmon. There is the possibility that the salmon louse has co-adapted to the domestic strain of salmon, or alternatively, that selective breeding over generations of salmon farming has produced a phenotype that is physiologically vulnerable to infestation. From these results, I have shown that behaviour provides a means of protection against infestation in an intensively farmed fish, which opens the potential for behaviour to be incorporated into aquaculture management practices. The aquaculture industry, of Atlantic salmon but also other finfish species, provides a substantial proportion of the global demand for animal protein. Aquaculture’s use of and effect on natural resources is at a much more sustainable level compared to terrestrial agriculture, and managing parasites with alternative methods than medicinal compounds will keep the industry’s trajectory aimed at minimal environment impacts and positive animal welfare.
-
ItemConservation genetics of the Growling Grass Frog, Litoria raniformis, in urbanising landscapes( 2016)The proportion of the world’s human population living in cities and towns (urban areas) grew rapidly over the 20th century. Indeed, the global urban population grew by an order of magnitude during this period, from 220 million to 2.8 billion. By 2030, the global urban population is expected to swell to almost 5 billion. Urbanisation is a key threatening process for amphibians, with the global amphibian assessment listing greater than one-third of the world’s known amphibian species as currently threatened by urbanisation. As is the case for biodiversity more generally, habitat loss and fragmentation represent pervasive impacts of urbanisation for amphibians. The International Union for Conservation of Nature (IUCN) recognises genetic diversity as one of three forms of biodiversity requiring conservation. However, surprisingly few studies have focused on the genetic consequences of urbanisation for amphibians. With the global rate of urbanisation set to steadily increase, and its recognition as a key threatening process to amphibians, the application of genetic techniques will be an important component of conservation planning for these animals. This thesis investigates the conservation genetics of the Growling Grass Frog, Litoria raniformis, around Melbourne, Australia. This species has declined significantly since the late 1970s, largely due to habitat loss and fragmentation, drought and disease. Remnant populations around Melbourne occur in four main regions, three of which are marked for urban growth, causing further loss, degradation and fragmentation of habitat for L. raniformis. The aim of this thesis was to assess the genetic structure and diversity of remnant populations of L. raniformis across Melbourne. There were four main objectives: 1. Assess four different genetic sampling techniques for amphibians, using a multi-criteria decision framework and L. raniformis as a case study. 2. Document the genetic structure and diversity of L. raniformis across Melbourne’s urban fringe, using mitochondrial DNA (mtDNA) and microsatellites. 3. Investigate the population genetic structure of L. raniformis in the northern region of urbanising Melbourne and develop a model of the landscape determinants of gene flow for the species. 4. Undertake a Bayesian metapopulation viability analysis for L. raniformis, incorporating estimates of gene flow to define population connectivity. The thesis concludes by outlining directions for further research on the conservation genetics of the Growling Grass Frog and its management.
-
ItemA genetic approach to the conservation of holly leaf grevilleas (Proteaceae)( 2016)The holly leaf grevilleas consist of an informal aggregate of 15 species found in south-eastern Australia. The group exhibits high levels of morphological variation and the most widespread species, Grevillea aquifoilum Lindl., is also the most variable. Most species are restricted endemics and their geographic limits make them vulnerable to the effects of fragmentation and environmental change. In some species, production of viable seed is unknown or has not been confirmed. Identifying factors that contribute to the persistence of species when fecundity is low is of critical importance to their conservation. Here, a phylogenetic analysis is used to clarify the evolutionary relationships among lineages within the holly leaf grevilleas. The lineages identified are then the basis of chapters 4 – 6 that address questions of what constitutes the units of conservation and how clonal plants should be assessed. Analysis of 12 cpDNA regions strongly supported the more southerly distributed holly leaf grevilleas as a monophyletic group comprising four clades (‘G. aquifolium’, ‘G. dryophylla’, ‘G. repens’, ‘G. ilicifolia’). The two northern holly leaf grevillea species, G. renwickiana and G. scortechinii, found in New South Wales and southern Queensland, were not positioned with the southern species but their relationship with outgroup species G. willisii from northeastern Victoria and G. acanthifolia and G. laurifolia from New South Wales could not be ascertained with confidence. Two nuclear regions, PHYA and waxy1, were less variable and not analysed in combination with cpDNA. PHYA was largely uninformative with most species forming a polytomy. Two major variants were identified in waxy1 and consisted of one functional and one non-functional copy based on DNA translation. Minor alleles of functional and non-functional copies were present in some accessions. Using only the functional copy (including multiple alleles when present), the southern ‘G. ilicifolia’ clade, as identified from cpDNA, was clearly differentiated from the northern clade and the remaining species. Within the southern species, those not belonging to the ‘G. ilicifolia’ clade were grouped together but clades identified in the cpDNA phylogeny were not recovered in the waxy1 analysis. Incongruence between the phylogenetic placement of some taxa and current species assignment based on morphology, including apparent paraphyly of G. aquifolium, may indicate an evolutionary history of hybridisation, introgression and incomplete lineage sorting and/or the use of morphological characters that are not lineage-specific. For example, the two subspecies of G. montis-cole differentiated morphologically on the basis of style-length are positioned in different clades and warrant specific rank if supported with nuclear data, and G. steiglitziana is split between two lineages within the southern ‘G. dryophylla’ clade. The phylogenetic placement of G. ‘williamsonii’, a taxon no longer recognised, with sympatric G. aquifolium, coupled with microsatellite analysis supports the current taxonomic view of its synonymy with G. aquifolium. The cpDNA phylogeney also raises questions about the taxonomy of G. microstegia and G. bedggoodiana, taxa that are also positioned with G. aquifolium in the ‘G. aquifolium’ clade. Population genetic analyses of G. infecunda and G. renwickiana found both species to be comprised of a small number of clonal lineages with no evidence of contemporary sexual reproduction. Within species, no clones were found at multiple locations and cpDNA haplotypes were derived from single lineages. In G. infecunda, 38 clonal lineages were identified from a microsatellite analysis of 280 samples from 11 populations. The number of clones present per population ranged from 1 to 11 and clone size varied from a single stem to several hectares. In G. renwickiana, analysis of 197 samples revealed that all but one of seven populations were monoclonal. Clones were distributed over a minimum area of one hectare. Sequencing of microsatellite alleles showed that variation in allele size profiles among clonemates could be interpreted as somatic mutation. The genetic patterns evident in the two species are likely to be the result of a loss of sexual reproduction, due to pollen sterility in G. infecunda and the effects of triploidy in G. renwickiana. For the clonal taxa, G. infecunda and G. renwickiana, lack of sexual reproduction leaves little opportunity for adaptation or migration in response to changing conditions. However, to facilitate the adaptive responses of ecological communities rather than individual species, conservation should encompass obligately clonal species because of their role, albeit finite, in mitigating ecological instability as floras respond to rapidly changing environments.