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ItemNo Preview AvailableStructural evolution and hydrocarbon play fairways of the Gippsland basin(University of Melbourne, 2003)
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ItemRelationships among plant communities and underlying soil and water conditions in the Alcoa Lease area, Anglesea, Victoria(University of Melbourne, 2003)The Alcoa Lease Area (ALA) in Anglesea, Victoria comprises about 2250 hectares of indigenous heathy ecosystems with local, national and international significance. Open-cut mining operations within the ALA disturb approximately 7% of the total area. Ultimately, a large, man-made water body and reconstructed soil profiles will remain as the legacies of mining activities in the lease area. In accordance with the requirement of Alcoa of Australia to rehabilitate disturbed land, Alcoa in conjunction with Parks Victoria has developed a management plan for the lease area. Prior to this study there has been inadequate edaphic and hydrological data on these ecosystems to develop more detailed, site-specific strategies. Heathlands in Mediterranean-type ecosystems worldwide have relatively low nutrient status and are adapted to extreme seasonal fluctuations in water availability. In upland situations, heathy plant species survive dry conditions during summer and waterlogged conditions during wet seasons. In contrast, wetland-type heathy ecosystems grow in soils with high organic content, relatively greater ranges in nutrient concentrations and under saturated conditions throughout the year. Due to limited ranges in nutrient availability and the extremes of water availability tolerated by heathy species, site-specific strategies should be determined by the capacity to restore edaphic and hydrological conditions. Previous studies comparing environmental variation among community types across local landscapes have shown that no single variable controls distribution patterns. Rather, quantification of a range of edaphic, hydrological and climatic variables is required to predict distribution. The aim of this study was to assess the hypothesis that edaphic and hydrological parameters influence the discrete distribution of heathy ecosystems in the ALA. Results from this study show that even across the broad range of edaphic and hydrological parameters examined here, one variable alone does not determine the discrete distribution of the Bald Hills Heathland and Heathy Woodland. Soils supporting these communities had similar profile characteristics [Northcote, 1979 #938] and soil chemical properties (total N and P, C, C/N, CEC, major cations (Ca, Mg, K, Na) sum of exchangeable cations and soil pH) to 2 m in depth and had similar concentrations of NH4+ and NO3 in surface soils (0-5 cm). Soil moisture contents, water table fluctuations and the concentrations of major cations (Ca, Mg, K, Na) in groundwater were also similar. Heathland and woodland soils were similar to those supporting the Closed Shrubland in pH, concentrations of total P and of C/N ratios. In contrast to the duplex soils of upland communities, soil supporting the Closed Shrubland was organic and had significantly greater concentrations of nutrients. In addition, unlike the considerable seasonal variation in soil moisture contents in upland communities, sub-soils underlying the Closed Shrubland were permanently saturated and surface soils were often flooded during winter. The rate of N mineralised was the only ecological parameter examined that varied significantly among all three heathy communities. Rates of N mineralisation were greatest in the Closed Shrubland (69 ?g g-1), followed by the Heathy Woodland (34 ?g g-1) and least in the Bald Hills Heathland (17 ?g g-1). These community differences most likely reflected differences in species demand for available N and rates of N turnover. Differences in N isotope signatures among genera from heathy communities suggests that mycorrhizal associations and internal recycling of N within plants can have a strong influence on N cycling. For example, mycorrhizal symbiosis is most likely responsible for the 15N-depleted foliage of the genera Eucalyptus and of Leptospermum from upland communities. In contrast, 15N-enriched foliage of non-mycorrhizal Gahnia suggests a strong influence of internal recycling. In the Closed Shrubland, mycorrhizal fungi are largely inactive due to waterlogged soil conditions. In this light 15N-enriched foliage of genera from the Closed Shrubland further support the suggestion the influence of internal recycling. A range of methodologies was used to elucidate patterns and process of nutrient-use efficiency for a range of genera from heathy communities. Foliar N:P ratios of all genera examined in this study were indicative of ecosystems for which plant growth is limited by P (Koerselman 1996). This proposition was also supported by data for resorption efficiency with between 78 to 95% of P withdrawn from green foliage prior to leaf senescence. The resorption efficiency of P was considerably greater than for other elements examined including N and K. Similarly, indices of P-use efficiency were between 40 to 350 times greater than for N and K. Differences in water-use efficiency, estimated as foliar-?13C, was related to plant life form, root architecture and access to water sources. Greater water-use efficiencies of shallow- rooted plants from the upland sites were indicative of a considerable reduction in available water sources during summer and are illustrated by seasonal differences in foliar-?13C values. In contrast, deep-rooted species and those from wetlands with permanently waterlogged soils were less efficient in their water-use and exhibited no seasonal variation in foliar-?13C values. Gahnia, which is shallow-rooted, was more responsive to seasonal changes in environmental conditions, including water availability, than were eucalypts and Leptospermum species. Redox potentials also reflected complex environmental conditions. Despite waterlogged conditions for at least part of the year, soil structural properties were able to maintain aerobic conditions in surface soil (0-5 cm) in all communities throughout the sampling period. Foliar ?15N for genera examined in the ALA indicate that mycorrhizal symbioses have a major influence on discrimination between N isotopes. This study supports the hypothesis that internal recycling is a further strong influence on ?15N in non-mycorrhizal species and in mycorrhizal species growing in conditions where mycorrhizal fungi are inactive. Whilst the distribution of heathy communities in the ALA was not delineated by soil P concentrations, soil P limited plant growth. Foliar N:P ratios of genera across community types were above the threshold indicating P limitation. This study add support to the use of N:P ratios of foliage as a useful indicator of P and N limitation in low-nutrient ecosystems. This study examined differences among heathy communities for a range of environmental properties to determine which factors influence the discrete distribution of communities. Geomorphology and hence nutrient and water availability strongly influence the distribution of upland communities compared with the Closed Shrubland. However, the distribution of the heathland and woodland was not related to the range of edaphic and hydrological parameters tested. In the absence of major edaphic and hydrological differences between the heathland and woodland, wildfire is the most likely factor controlling distribution of these communities.
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ItemThe Function of the apicoplast in the malaria parasite, plasmodium falciparum(University of Melbourne, 2003)Apicomplexan parasites such as Plasmodium falciparum and Toxoplasma gondii contain a relict plastid (the apicoplast) homologous to chloroplasts of plant and algal cells. The apicoplast is essential to parasite survival, but its function is unknown. Numerous nuclear-encoded proteins are translocated into the apicoplast courtesy of a bipartite N- terminal extension. This extension consists of a signal peptide and a transit peptide, but transit peptides are only poorly understood. I identified more than one hundred apicoplast proteins from Plasmodium falciparum and other apicomplexan parasites to learn more about their transit peptides. I found that although apicoplast transit peptides share some properties with plant chloroplast transit peptides, some features are distinctive to apicoplast proteins. I also extracted amino acid features from P. falciparum apicoplast transit peptides that distinguish them from other non-apicoplast P. falciparum proteins. This allowed the development of automated tools to recognise apicoplast proteins from raw sequence. I used a combination of pre-existing and custom designed bioinformatic tools to identify 545 putative apicoplast proteins from the Plasmodium falciparum genome. Expression of all genes that encoded predicted apicoplast proteins was analysed using oligonucleotide microarrays, revealing some groups of differentially expressed genes. The putative apicoplast proteome brings to light enzymes responsible for almost complete pathways for fatty acid, isoprenoid and haem biosynthesis. The apicoplast pathways, like those of chloroplasts, are bacterial in nature and offer excellent targets for antimalarials.
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ItemMaking decisions on genetically modified crops using quantitative risk assessments and benefit cost analysis(University of Melbourne, 2003)In Australia the Gene Technology Act, through the Gene Technology Regulator, governs research, development, and commercialisation of all transgenic organisms including genetically modified (GM) crops. The Gene Technology Regulator makes decisions regarding the environmental release of GM organisms after consultation with the Gene Technology Technical Advisory Committee (GTTAC). The Regulator is also responsible for preparing risk assessment and management plans. From a risk analysis point of view there are three fundamental problems with the current approach to decision-making: (1) Regulations to the Act specify that GTTAC decisions use majority voting; (2) the Regulator uses subjective risk assessments because the Regulator views quantitative approaches as having limited value due to a lack of direct ecological data; and (3) the Regulator does not consider the potential benefits of GMO releases. In other words, the underlying philosophy of the Act appears to be one of containment of risk rather than the more comprehensive philosophy of balancing the overall social costs and benefits of licensing a particular GM organism. In addressing (1) extensive use is made of social choice theory, providing a framework for analysing the consequences of majority voting - which fails to report uncertainty within the expert committee and may lead to unsatisfactory outcomes. An alternative approach is suggested, based on elicitation of expert opinions and reporting of uncertainty. In addressing (2) a statistical approach is developed that deals with the problem of setting assumptions where there is a lack of direct ecological information. A modelling approach is also developed for calculating gene flow and invasion that may form the basis of quantitative risk assessments for GM crops. In addressing (3) the importance of including benefits is illustrated by using benefit-cost analysis to evaluate the likely behavioral response of individuals to regulations promulgated by the regulator.
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ItemThe functional relationships between temperate fishes and the associated seagrass landscapes(University of Melbourne, 2003)Seagrass occurs commonly in both the intertidal (Zostera mulleri) and subtidal (Heterozostera tasmanica) regions of Port Phillip Bay, Victoria, and may form the primary structural habitat for benthic fish assemblages. Beds of seagrass do not exist as homogenous meadows, but rather are spatially complex, forming patches at a range of scales interspersed within an unvegetated sand matrix. In addition, these beds are temporally variable and susceptible to seasonal reductions and anthropogenic disturbances. The functional relationship between fish assemblages and seagrass areas is also likely to be spatially complex, and will to some degree reflect the underlying spatial structure of the system. In this thesis I took a multi-scaled observational and experimental approach to quantify the functional relationship between demersal fishes and shallow seagrass areas. I first used a spatially explicit approach to quantify which scales appeared to be important in explaining fish-habitat association. I established 185 geo-referenced sampling stations within a 2 x 1 km spatial array, and seined fish and measured depth and habitat variables at each station. To identify the relative importance of habitat (physical and biotic) given the spatial structure of the system, I sequentially modelled the main and interactive effects of spatial location, physical habitat structure, and biotic habitat structure for each species using a combination of regression, autocovariance modelling, and kriging techniques. Depth, seagrass density and seagrass length varied spatially across the array. Both large-scale spatial gradients (alongshore and offshore trends) and short-order spatial autocorrelation were identified. Fishes were generally associated with habitat variables that were intrinsically spatially structured. In addition, one species of pipefish and juvenile King George whiting displayed additional spatial patterns independent of habitat. This initial study descriptively modelled the relationships between fish and seagrass at scales of 0.3 to 2 km, and also identified that the fish-habitat relationship involved a large-scale (>2 km) component, in addition to finer scale (<0.3 km) autocorrelative components. Understanding how and at what scales organisms respond to their environment can provide substantial insight into how subsequent environment changes may alter the assemblage. To identify how larger scaled spatial and temporal trends and habitat parameters interacted to structure the fish assemblage, I undertook a multi-scaled spatio-temporal survey. In this study I sampled both cryptic and motile fishes and recorded the habitat both independent of the fish and directly beneath each fish (latter from diving samples only) from seine and diving samples at 12 sites situated at 2.5 km intervals alongshore, and 4 distance zones located every 250 m offshore. I sampled this array every season, for two years. Habitat, at large scales (km�s), was spatially structured both alongshore and offshore; there was also a small temporal pattern that operated independently of this spatial structure. The distribution and abundance of 90% of the fish species were explained either directly or indirectly by seagrass. A number of species were directly associated seagrass, for example long-dense seagrass. In contrast, other species were associated with the level of seagrass fragmentation rather than the direct presence of seagrass per se. While, habitat variables explained most of the fish assemblage structure, the presence of seagrass alone was not a sufficient predictor of fish, nor was there a typical �seagrass-fish� response. Instead, fish responded to specific habitat classes (e.g., seagrass, patchy seagrass, mixed habitats, or sand areas), but these habitats were often found in specific alongshore and offshore locations, consequently restricting the distributions of the associated fish species. In addition some fish species were also spatially distributed alongshore and/or offshore independent of habitat (e.g., some pipefishes). Temporal patterns were also important, but operated independently of both habitat and space at this scale (km�s). By studying fish-habitat associations at intermediate and fine-scales, I began to identify the specific habitat parameters that fish were actually associated with. At intermediate-scales, I more clearly identified the degree of habitat patchiness fish species were associated with, and the level of habitat selectivity. While, at a fine-scales I identified that the use of microhabitat parameters (patch-interior, edge, gap) by fish species varied. The information of fish-habitat associations at each scale added novel and valuable information, and when combined provided a much greater understanding of how each fish species and the assemblage as a whole responded to the underlying complexity of the habitat. Fish species utilized seagrass areas during different stages of their life history. To identify the population dynamics and possible ontogenetic shifts in habitat use, I measured the size of fish during the spatio-temporal survey. Species abundances varied dramatically between seasons, but were driven by different demographic characteristics. Some species recruited to seagrass areas, but later emigrated to other habitats. Other species recruited to, bred and then senesced in seagrass, while others species (e.g., pipefishes) spent their entire life cycle in seagrass areas. Ontogenetic shifts in habitat use occurred for several species. Fish species utilized different parameters of the seagrass habitat over different stages of their life. For example newly settled seagrass odacids N. balteatus (<2.5 cm) were found in dense seagrass or algae microhabitats, while large individuals were more frequently clumped within edge and gap microhabitats. Similarly, newly settled King George whiting (<3 cm) were associated with seagrass and gaps, 5-9 cm fish were almost only found in gaps within seagrass beds, while larger individuals (> 9 cm) aggregated together in motile schools and were associated with a range of habitats, although gap use was still high. These shifts in habitat association identified that both seagrass cover and habitat fragmentation were important to many fishes but that this importance varied over different phases of their life history. To determine how fish abundance and species richness change in relation to seagrass cover and the level of fragmentation, I experimentally removed different amounts of seagrass (reduced by 16% and 32%) in different spatial configurations (high and low fragmentation) from within four clusters of five 10 x 10 m permanent quadrats. This factorial design enabled disturbance area to be examined independently and interactively with disturbance patch size. Motile fishes were sampled using visual counts while cryptic fishes were non-destructively sampled using a small underwater seine. All fishes were sampled before and three times post-disturbance. Species responded in characteristic ways to experimental disturbance. Seagrass associates (leatherjackets and pipefishes) were either restricted to or more abundant in seagrass microhabitats and consequently abundance decreased with the loss of seagrass. This was contrasted by increased abundance and diversity of edge and gap associates, such as the odacid N. balteatus and King George whiting S. punctata. Gap size was also important. Several species responded to small gaps sizes (4 m2) and the edges of the larger gaps (16 m2) while subadult King George whiting (> 9 cm fishes) exhibited a threshold response, using only large gaps. In additionally, these responses changed with ontogenetic changes. Newly settled N balteatus were found predominantly within the seagrass matrix while larger individuals were found in all microhabitats, commonly focused within and around the edges of gaps, and in contrast to newly settled N. balteatus the abundance of larger individuals increased linearly as seagrass was removed. Despite some assertions, seagrass beds are not homogenous entities. Instead, they form a mosaic that is structured at many different scales. This has important implications for fish communities. In this study I identified changes in the strength and form of fish-habitat associations at scales ranging from meters to kilometers. The observed distribution of fishes in space is a complex array of different habitat elements. There is a deterministic element in which fishes respond to particular biotic habitat components such as seagrass cover or bed patchiness. However, these associations may be modified by the physical structure and the location along the shore of that biotic habitat. Additionally, there is a large-scale temporal dynamic that operates across all scales examined. In other words, the association of a fish with its �preferred� habitat is conditional on a suite of different landscape elements, which may operate additively, or synergistically. This study highlights that measuring the association between organisms and their habitat requires many levels of information, ranging from an understanding of the individual habitat preferences at the fine-scale, to understanding the spatially- explicit structure of fish and habitat at landscape levels. Understanding and predicting fish assemblage structure in the face of habitat change is no simple task, and relies heavily on the integration of fine scale empirical and landscape level studies, but this study demonstrates it is achievable.
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ItemEcological effects of offspring size in marine invertebrates(University of Melbourne, 2003)In attempting to understand variation in the distribution and abundance of marine populations, over 2 decades of research has focused on the effects of variation in the supply of new individuals into those populations. �Supply-side� ecology has explained much of the variation observed in many natural systems. Although the contribution of supply-side ecology is clear, explaining variation in the supply of recruits has been less successful. Variation in larval quality is one relatively unexplored source of variation in the supply of recruits. To date, the principal recognised source of variation in larval quality has been delayed metamorphosis. Another recently identified source of variation in larval quality is larval size. It appears that variation in the size of larvae can have profound effects on the subsequent performance of adults although data are extremely scarce. I investigated sources of variation in larval size and the consequences of this variation in a number of marine invertebrates. I examined the effects of larval size on each life-history stage for a number of sessile species that typically inhabit man-made structures in bays and sheltered ports. The majority were colonial species and all had non-feeding larvae. To examine the effects of larval size on post-metamorphic performance, I measured larvae in the laboratory and then transplanted the metamorphosing juveniles into the field where I assessed their performance, in some cases through to reproduction. I examined sources of variation in larval size for 6 species of marine invertebrate from 3 phyla. For these 6 broadcasting spawning species, I found that there was substantial intraspecific variation in offspring size and this came from 2 sources. For the ascidians Pyura gibbosa, Styela plicata and Ciona intestinalis, and for the asteroid Uniophora granifera I found that egg size was correlated with maternal body size. For the ascidian C. intestinalis, the echinoid Arbacia punctulata and the polychaete Galeolaria caespitosa I also found that the size of larvae that are produced was strongly dependent on the sperm concentration in which they were fertilised. At low sperm concentrations, larger eggs were more likely to be contacted by sperm and so the larvae that were produced were, on average, larger. At high sperm concentrations, larger eggs were more likely to become polyspermic whereas smaller eggs were more likely to be successfully fertilised and so, on average, smaller larvae were produced. From these results, I concluded that for marine invertebrates that reproduce by free spawning, larval size is likely to be highly variable and influenced by local population density and the size distribution of reproductive adults. I examined the consequences of variation in larval size for 4 other species covering 2 phyla, 3 were brooders and 1 was a broadcast spawner. I found variation in larval size had strong effects on the subsequent performance of juvenile and adult marine invertebrates. For the bryozoan Bugula neritina I found that colonies that came from larger larvae survived better, grew more and had higher reproductive outputs than colonies that came from smaller larvae. Interestingly, these effects crossed generations, larger larvae became larger colonies that in turn produced larger larvae. I found these effects in 2 very different habitats (temperate Australia and sub-tropical U.S.A.) although the strength and consistency of these effects varied between the 2 habitats. I found similar effects of larval size for the bryozoan Watersipora subtorquata and the ascidian Diplosoma listerianum, with colonies originating from larger larvae generally having higher survivorship and growth although again, these effects were strongly mitigated by the habitat. On artificial settlement plates, larval size had persistent effects on mortality but not growth in W subtorquata. On pier pilings the following year, larval size affected growth but not the mortality of W subtorquata colonies. I also compared the magnitude of the effect of delayed metamorphosis and larval size on subsequent colony performance in W. subtorquata and found that larval size had stronger effects than delaying metamorphosis for 6 hours. For the solitary ascidian Ciona intestinalis, I found that settler size (which reflected larval size) strongly affected the post-metamorphic survival of juveniles in the field. Larger settlers were much more likely to survive than smaller settlers. This effect was exacerbated by increases in the density of conspecific competitors. When densities were high, the survival advantage of larger settlers was increased. It seems that in this species, increased per offspring investment results in greater competitive ability. Larval size also affected the duration of the larval period in the bryozoans B. neritina and W. subtorquata and the ascidian D. listerianum. Larger larvae took longer than smaller larvae to attach and metamorphose in the laboratory in the absence of any known settlement cues. In the presence of simple settlement cues, larger larvae could settle sooner but still took longer to settle than smaller larvae. These results were reflected in the field for W. subtorquata, where larger larvae settled later than smaller larvae and were more discriminating than smaller larvae, with a greater proportion of larger larvae settling on preferred settlement surfaces. Increased discrimination of larger larvae may have the effect of increasing their dispersal potential. I had found that larger B. neritina larvae become larger colonies that in turn produce larger larvae themselves. This �grandparent effect� could be due to anatomical or physiological constraints, genetic or early maternal effects or could be a plastic trait. To determine if larval size was a plastic trait, I manipulated colony size independently of larval size and genetics using 2 techniques and then compared the size of the resultant offspring to controls. First, I manipulated colony size immediately prior to reproduction by halving the colonies in a way that left the ratio of feeding zooids to reproductive structures unaltered. The second technique involved artificially delaying the metamorphosis of some larvae, thus reducing post-metamorphic growth. Using both techniques I found that larval size was strongly dependent on current colony size and appeared to be a plastic trait. It seemed that maternal colonies were reducing their investment in offspring in order to increase their own size and thus fitness. In B. neritina, it appears that larval size is plastic trait that can be manipulated by the maternal colony and consequently, maternal influences in this species can be remarkably pervasive. I found that larval size can be highly variable, due to a range of different factors. This variation has important consequences for the species examined here and has the potential to explain much of the variability in recruitment of marine invertebrates.
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ItemThe harpacticoid copepod fauna of Port Phillip Bay (Victoria, Australia) and their contribution to the diet of juvenile King George whiting (Sillaginodes punctata: Sillaginidae)(University of Melbourne, 2003)Harpacticoid copepods are minute crustaceans that are found in virtually all marine environments. In Port Phillip Bay (Victoria, Australia) they are abundant and diverse, forming a large proportion of the meiofaunal community that lives in the seagrass beds and adjacent unvegetated habitat. Meiofauna is the term given to invertebrates in the size class of 45 ?m to 500 ?m. In spite of then- abundance, little is known of the harpacticoid fauna of Australia. World-wide there are over 3000 species of Harpacticoida, but prior to this study only 94 species had been documented as occurring in Australia, including three species from Port Phillip Bay. The crustacean fauna of southern Australia (e.g. isopods and amphipods) is speciose and highly endemic (Gray et al., 1997) and if the same is true for the harpacticoids, it can be anticipated that there remains a large number of species to describe. In Port Phillip Bay, among seagrass and on unvegetated sediments 59 species from 33 genera and 16 families were recorded and many of these are new to science. Harpacticoid copepods form the major component of the diet of juvenile King George whiting (Sillaginodes punctata) during the first few months after the fish settle out of the plankton. The harpacticoid literature is vast and not easily understood by the non-specialist and with so few Australian species described, fisheries scientists have been limited in their exploration of the diet of S. punctata as they are rarely able to identify the copepods beyond the taxonomic level of order. This thesis provides a preliminary guide to the harpacticoids of Port Phillip Bay�s shallow subtidal seagrass beds (Heterozostera tasmanica) and associated unvegetated habitats. It includes brief diagnoses of 16 common species with many illustrations and an illustrated glossary of terms. In addition, a detailed description of a new species of Parastenhelia and a redescription of Parastenhelia spinosa is included with a review of the family Parastenheliidae. Phylogenetic analyses showed that if the family was to be monophyletic, Karllangia had to be synonymised with Parastenhelia. Description of Porcellidium poorei is included with a new review of the family Porcellidiidae. Two new species from the genus Scutellidium (Tisbidae) are described and the genus is reviewed. The new knowledge of the harpacticoid fauna of Port Phillip Bay was used to examine harpacticoid assemblages in the environment and in the diet of S. punctata in more detail than previous studies. The combined effects of habitat, location and month on a) epifaunal harpacticoid assemblages in the environment and b) harpacticoid assemblages in diet of juvenile S. punctata collected over shallow, subtidal seagrass and unvegetated sediments at six sites in Port Phillip Bay between September and November 1997 were examined. Harpacticoid assemblages sampled from seagrass and unvegetated habitats were compositionally (taxonomically) distinct, but could not be consistently distinguished in terms of species richness or abundance. In September the diet of juvenile S. punctata was dominated by calanoid copepods, but by October the diet consisted almost entirely of harpacticoids. The gut contents of juvenile S. punctata collected from seagrass and unvegetated habitats were indistinguishable in terms of taxonomic composition and abundance and resembled harpacticoid assemblages found among seagrass to a greater degree than those collected over unvegetated sediments. This indicated juvenile S. punctata fed primarily among seagrass, regardless of what habitat they were caught in. Further analysis of the gut contents indicated S. punctata fed selectively, sometimes targeting rarer species, while ignoring more common ones. Thus counts of harpacticoids at the taxonomic level of order may provide inaccurate measures of food availability, particularly if species abundant in the environment are rarely eaten by S. punctata.
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ItemParallel algorithms for lattice enumeration problems(University of Melbourne, 2003)
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ItemMutual ornamentation and the behavioural ecology of black swans(University of Melbourne, 2003)This thesis describes the behavioural ecology of a native waterbird of Australia, the Black Swan, Cygnus atratus. Both sexes of this species possess ornamental wing feathers, and a central aim of my work has been to identify potential selection pressures that may have contributed to the evolution and maintenance of such mutual ornamentation. In the wild population I studied, Black Swans typically formed socially monogamous pair bonds, 94% of which persisted between breeding seasons. Breeding attempts by single males or single females and polygamous and homosexual associations (which occurred regularly in a captive population studied previously by Braithwaite 1981b), were rarely observed in my study population. The curled wing feathers found in both male and female Black Swan have no obvious survival benefit and are therefore considered as �ornaments�. These ornamental feathers become most conspicuous when the wings are lifted during display, in particular agonistic displays and the triumph ceremony. While the purpose of agonistic displays is clear, the function of triumph ceremonies remains controversial. I conducted detailed behavioural observations of both naturally occurring and experimentally induced triumph ceremonies. These observations suggested that triumph ceremonies function primarily as a cooperative threat signal in the Black Swan. I found that agonistic interactions between birds of the same sex and reproductive status were most frequently won by more ornamented individuals. Furthermore, �residency� status (a measure of the ability of breeding pairs accompanied by cygnets to monopolise feeding areas), was associated with significantly enhanced offspring survival. Resident pairs had more curled feathers than itinerant pairs, so the curled feather ornament appears to have an indirect effect on reproductive success. Furthermore, the ornament seems to be involved in mutual mate choice, because paired birds had more curled feathers than unpaired birds and individuals paired assortatively with respect to the number of curled feathers. This ornament thus appears to fulfil a dual function in signalling social dominance and attractiveness, because dominant birds are preferred as social partner. If males vary in quality and individual quality is heritable, females may benefit from engaging in extra-pair fertilisations with males of higher quality than their social partner. Using DNA micro satellite markers to assign parentage to cygnets, I found that up to 18% of offspring in the study population were not sired by the social father and 40% of broods contained at least one extra-pair cygnet. However, there was no evidence that females were seeking extra-pair fertilisations from males of higher quality than their social partner. Furthermore, levels of extra-pair paternity were not explained by ecological factors (breeding density or synchrony), or genetic factors (offspring viability or genetic relatedness between female and extra-pair/within-pair male). Therefore, there is as yet no compelling explanation for the high levels of extra-pair paternity in the Black Swan. Recent studies have shown that some bird species are able to bias the sex ratio of their offspring in relation to the relative fitness costs and benefits of sons and daughters. I sexed cygnets using a molecular technique and found that male and female cygnets had similar weights and sizes and that hence the relative costs of producing sons versus daughters are unlikely to differ. However, first-year survival was higher among males than females in one year of the study and males reached maturity in better body condition than females. Brood sex ratios did not correlate with the number of curled feathers of either parent. However, the proportion of sons was positively correlated with maternal condition. This finding is difficult to reconcile with our current understanding of Black Swan breeding biology. To investigate whether mutual mate choice may be a general explanation for mutual ornamentation in birds, I conducted a comparative analysis. The level of mutual ornamentation was found to be positively correlated to divorce rate. This supports the mutual sexual selection hypothesis, because high divorce rates are expected to lead to more frequent mate choice competition over mates. This result was robust to the removal of confounding effects of phylogeny, body size and life history variables. An investigation of the most likely scenario for the coupled evolution of mutual ornamentation and divorce indicated that from an ancestral state of high levels of both mutual ornamentation and divorce, mate fidelity evolved first, followed by the loss of mutual ornamentation.
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