School of BioSciences - Theses
Permanent URI for this collection
Search Results
1 - 4 of 4
-
ItemBreeding biology of the platypus (Ornithorhynchus anatinus)( 2018)This thesis examines the different behavioural stages of the reproductive cycle in the platypus, Ornithorhynchus anatinus, the time and energy investment of the female in breeding, and use of burrows by wild juveniles during the period after they first emerge. Many aspects of platypus reproduction are poorly understood due to their cryptic, nocturnal, semi-fossorial and semi-aquatic behaviour, which makes studies in the wild difficult. I studied a group of captive platypuses at Healesville Sanctuary and newly emerged juveniles from the wild population within Badger Creek, Victoria. My aims were to examine prey selection and seasonal energy intake, quantify and describe courtship, mating, nesting behaviour and maternal care given to nestlings, and describe how juvenile platypuses use the habitat in their natal home range. In captivity, platypuses consumed the fewest kilojoules during the breeding season and most kilojoules during the post-breeding breeding season. They showed a preference for less-mobile prey (mealworms, earthworms and fly pupae). Crayfish formed the largest quantity of food in the diet and was highly nutritious for energy (kJ), vitamins and minerals. The platypus diet was influenced by nutritional content, the stage of the breeding season and the behaviour of the prey species. Female platypuses controlled breeding encounters with males via three strategies; avoidance, by having lower activity levels and changing their activity pattern to partially diurnal; flight, by leaving the area immediately upon encountering the male; and resistance, terminating breeding encounters with the male and using a non-contact courtship behaviour prior to contact courtship behaviours. These strategies are likely to protect females from injury and coercion. After mating, females invested 8 ± 1.5 hours over 3 nights collecting wet vegetation for their nesting burrow. The morphology of burrows varied each year, but contained the same structural features: narrow tunnels, dead ends, ‘pugs’ of backfilled earth and multiple entrances that lead to a nesting chamber containing a spherical vegetation nest. The female’s energy intake increased to twice that of a non-lactating female in the final month of lactation, indicating the high cost of milk production. The length of lactation dependence for platypus nestlings was 128 ± 1 days. Females spent less time in the nest with twins compared with a single nestling. I developed an infra-red camera technique which allowed platypus nestling behaviour, growth and development to be observed in their burrow. Weaning occurred as an instantaneous event when the nestlings emerged into the water. Newly emerged wild juvenile platypuses each used multiple burrows for single or multiple nights within their natal home range. There was no significant correlation with vegetation communities along the bank at burrow sites, indicating burrow site selection was not driven by vegetation structure. No juveniles dispersed, suggesting they persist in the natal home range until the sub-adult stage which may assist their survival as they develop their skills and complete their growth in high quality habitat. My study demonstrates that female platypuses invest a high amount of time and energy in breeding, from avoiding the male platypus, through courtship and mating, creating the nesting burrow, maternal care during lactation, and while juveniles persist in her home range after weaning. I have provided captive management recommendations based on my research to advance the animal welfare and captive breeding success of the platypus.
-
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.
-
ItemThe temperature and water dynamics of reptiles in changing climates( 2017)The dynamics of heat and water flux through the biosphere are fundamentally interconnected and together determine environmental and biological processes across vast scales. However, despite the physical ties between heat and water dynamics, the biological implications of temperature change are most often considered independently of precipitation change. Thermal stress is predicted to drive global extinctions of ectothermic species as high as a 20% species loss. Yet these predictions disregard the potential for simultaneous changes in precipitation and aridity to cause additional stress for ectotherms. With few exceptions, water loss rates of ectothermic species are positively correlated with temperature and can be substantial, meaning hydric stress is expected to increase with thermal stress. My goal was to determine how species might respond to hydric stress brought on by changing climates. Using a combination of empirical and modelling approaches, I investigated the influence of water budgets on the physiology and behaviour of ectothermic species. I begin by describing a mechanistic model of evaporative water loss rates, an important part of an ectotherm’s water budget, which can be parametrized with species specific physiological data. I validated the model’s predictions of evaporative water loss rates against a database of experimentally collected data for 39 species of squamate reptiles. I also compiled existing data which can be used to fit water budget models for an additional 103 reptile species. Next, I applied an integrated heat and water budget model to predict the influence of several physiological and behavioural hydroregulatory mechanisms on the water budgets of two closely related yet ecologically disparate Australian skinks, Liopholis striata and Egernia cunninghami. My results suggest that behavioural mechanisms can be equally important to regulating water balance as physiological mechanisms. Moreover, I found substantial variation in the amount of water conserved via each hydroregulatory mechanism between the two species, suggesting that a species’ vulnerability to climate change will also show strong variation across habitat and lifestyle. The water budget model’s predictions hint to the potentially strong influence of an often disregarded avenue of water loss on reptilian water budgets: the wet surface of the eye. I measured ocular water loss rates for the arid zone Australian skink, Liopholis inornata and found that ocular evaporation can instantaneously surpass both cutaneous and respiratory evaporation, reaching up to 65.8% of total evaporative water loss. I also found evidence that two species of Australian arid zone skink regulate their ocular water loss by manipulating eye closure while basking in response to aridity, and estimated that this hydroregulatory behaviour reduced their overall evaporative water loss rates by almost 20%. The water budget model also predicts that activity patterns and retreat selection can strongly influence reptilian water budgets. I looked for experimental evidence of three hydroregulatory behaviours - retreat site selection, retreat patterns, and diel preference – being used by arid zone skinks Liopholis striata and Liopholis inornata, under different environmental conditions and hydration states. Both these species were previously thought to be primarily nocturnal, a relatively rare lifestyle for lizards other than geckos. I found that both species are neither primarily diurnal nor primarily nocturnal, and would be better described as crepuscular. Moreover, I found that both species reacted behaviourally to changes in humidity or hydration state. The behavioural responses were not consistent across species, but were always in directions consistent with the regulation of water budgets. Moreover, both species were always highly selective of hides that provide the most humid conditions. Ultimately, the application of the water budget model predicted that reptilian water budgets should be very influential to the behaviours, activity patterns and distributions of reptile species, and my experimental investigations have supported this prediction. However, we still know comparatively little about reptilian hydroregulation. Before we can predict the effects of changing climates on reptilian species, we must understand how animals regulate both their heat and water budgets, as both these aspects of their physiology have been shown to influence activity, and thereby ultimately influence the present and future distribution of reptiles.
-
ItemCoping style and group dynamics in a cooperative breeder, the superb fairy-wren (Malurus cyaneus)( 2016)Group dynamics – the movements and interactions of individuals within and between groups – are known to play an important role in influencing key life history events such as dispersal and reproduction. Nevertheless, there is considerable variation in conspecific interactions and life history strategies that remains poorly understood. Over recent years, a growing number of studies have shown that individual animals consistently differ in their behaviour over time and across contexts. This phenomenon is typically referred to as ‘animal personality’ or ‘temperament’ and evidence is accumulating that these behavioural differences can help to explain the form and expression of life-history traits. However, currently most evidence for a relationship between personality and life-history traits comes from theoretical or captive studies. There is a need to verify these ideas under natural circumstances, to assess the true impact of personality on individual life-histories and fitness. In this thesis I investigated whether and how individual coping style (a narrow-sense proxy of personality) is related to the performance of different tasks during breeding and to individual natal dispersal strategies in a wild population of cooperatively breeding superb fairy-wrens (Malurus cyaneus). In this species, males can disperse at any point in their life and help their parents raise successive broods while still at home, while most females disperse in their first year. By conducting behavioural assays, of fairy-wren behaviours (boldness, exploration, aggression) under controlled conditions, I first established that individual fairy-wrens in my population indeed show distinct coping styles. I then tested whether individual differences in coping style where related to contributions to key tasks within social groups, specifically alloparental care (nestling feeding behaviour), territory defence (responses to simulated conspecific territorial intrusions) and nest defence (responses to a novel object at active nests). To test for relationships between coping style and dispersal outcomes, I experimentally created temporary breeding vacancies by removing male breeders from territories without helpers to prompt dispersal by a male helper from one of the neighbouring territories into the vacant breeding position. Finally, I used data on natural cases of male and female dispersal, collected over six consecutive years of population monitoring to test whether individual dispersal strategies were related to coping style. My findings suggest that coping style has much less influence on group dynamics than suggested by theoretical and captive studies. First, cooperative division of tasks such as offspring provisioning and nest defence did not occur during breeding, nor did individuals consistently differ in the amount of help provided. Coping style did not affect feeding rate or response to a simulated conspecific intruder, and only played a role during inspection of a novel object near the nest when more than one bird was present: birds with relatively fast coping styles (exploratory, active and bold in the artificial environment) responded more strongly to the object than group members with slower coping styles. In general, the social context had the strongest effect on behaviour. Individuals responded much more strongly to the novel object and the simulated conspecific intruder when in the company of other group members than when alone. Second, coping style only played a role in dispersal among young males. Males that dispersed during their first year of life on average had a faster coping style than those that delayed dispersal. Among males that dispersed after their first year, dispersal timing was not related to coping style, but rather to the likelihood of inheriting the natal territory. In females, dispersal timing was not related to coping style, but rather to hatch timing. In superb fairy-wrens the social and physical environment seem to play a larger role than personality in how individuals behave within their group and in the dispersal decisions they make. Task division did not occur and individuals instead seemed to be flexible and responsive to environmental stimuli in relation to offspring care and defence. Investment in cooperation is therefore not a good predictor of life-history strategies in this species. With regard to dispersal strategies, males with faster coping styles indeed disperse or die young, as predicted by the pace-of-life syndrome hypothesis. Due to the reduced variance in coping styles among males that disperse later, variation in dispersal timing among these males is rather due to external factors such as stochasticity of dispersal opportunities and dispersal motivation based on conditions in the natal territory. For females dispersal is a prerequisite for reproduction, which leads to higher dispersal motivation compared to males. The importance of hatch date for dispersal timing indicates that environmental conditions outweigh coping style as a predictor of dispersal strategies. Together, these results show that theoretical and captive studies may overestimate the role of personality in life-history strategies in the wild by oversimplifying the environment. Captive studies may teach us about underlying mechanisms, but only by testing predictions in the field will we truly know their significance in individual life- histories and their consequences for evolution.