Zoology - Theses
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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.
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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.
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ItemLeadership behaviour in larval aggregations of the social sawfly Perga affinis( 2015)When animals group together, individuals can benefit through enhancement of thermoregulation, defence against predators, access to mates and foraging successes. However, sustaining group cohesion can be a challenging process. The emergence of individual leaders can help alleviate some of the difficulties involved in reaching group consensus and retaining group cohesion. In this thesis I explore the significance of leader and follower roles, focussing on how and why certain roles are maintained within the group. I do this by investigating the relationship between these behavioural roles and the growth, gender and knowledge of individuals, as well as the foraging timing of whole aggregations. Perga affinis larvae form dense aggregations wherein some larvae lead foraging movements more than expected by chance (leaders) and some larvae lead less (followers). To investigate the importance and influence of behavioural roles, I created larval aggregations that were comprised of all leaders, all followers or a mixture of the two. Individuals showed higher growth rates when in mixed aggregations than when in aggregations containing a single behavioural type. This finding highlights the importance of including the often-overlooked follower role when considering the benefits of leadership. In follower-only aggregations, some larvae became consistent leaders, suggesting a level of flexibility to the behavioural roles. Further, I propose that leadership in P. affinis may be correlated with gender, as males were predominantly found within follower aggregations whereas females emerged from leader aggregations. Theoretical models that consider leadership in animal societies emphasise the value of leading individuals possessing knowledge or experience to aid group decisionmaking. I empirically investigated the relevance of knowledge on leadership roles by establishing aggregations that contained leaders with and without knowledge of their environment (i.e. familiarity with their host tree). I found leaders resumed their role of initiating and leading group movements only when they were already familiar with the tree they were placed upon. However, knowledgeable followers never lead the aggregation, even when placed with conspecifics that have no knowledge of their environment. This suggests that both knowledge and prior experience are important aspects for an individual to maintain a leadership role. Finally, I examined whether the presence or absence of leaders influences the timing of the nightly aggregation foraging movement. Aggregations of only leaders or only followers did not significantly differ in their movement patterns. Instead, there was a strong link between temperature and the timing of movement: aggregations began foraging earlier and ceased foraging later on days when the ambient temperature was cooler. Thus, P. affinis aggregations appear to utilise the environmental cue of temperature in order to decide when to forage. The findings within this thesis highlight the significance of leadership and followership for various aspects of fitness and behavior within larval aggregations.Given the importance of leadership to even a very simple animal society, such as sawflies, the implications of this research could have far-reaching consequences for understanding how leadership influences and promotes collective decision-making.
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ItemSampling the social environment in an uncertain world( 2012)The world that we inhabit is characterised by variation in the environment over space and time. Subsequently, animals are faced by uncertainty regarding their current and future conditions. Thus, it is critical to understand the nature of responses to uncertainty. Theory suggests that animals incorporate information from their environment through natural selection or personal experience, and use this information to make decisions that anticipate environmental conditions. Animals also possess the ability to improve their estimation of current conditions by sampling for new information, and individuals that incorporate updated information can have an adaptive advantage over those that use older information. However, sampling can be costly and selected against. The use of sampling strategies can also depend on social interactions within a population, the structure of the landscape, and variation in spatial scale. This thesis considers the conditions in which it is adaptive for an individual to sample information from their social environment, and how this behaviour is affected by the landscape and the decisions being made by others. In particular, I explore the use of updated information from the social environment in three contexts in which fitness is dependent on the social environment and phenomena attached to the landscape. In Part I, I report the results of a field experiment on breeding site selection in the terrestrial toadlet Pseudophryne bibronii. I collected every calling male in a breeding population, released them into empty habitat patches, and observed the decisions that they made during re-settlement. I found that the decision to sample social cues when selecting breeding sites reflected a predicted relationship between the value of previously gathered information and spatial scale. In Part II, I conceptually explore the interaction between conspicuous features of the landscape, or landmarks, and the adaptive value of sampling the social environment by conducting a literature review on the adoption of landmarks for territorial boundaries. Additonally, I conducted a laboratory experiment on the ability for convict cichlids, Amatitlania nigrofasciata, to learn spatial associations between landmarks and contests. The results of these studies indicate that the effect of landmarks on sampling may depend on the process responsible for the adoption of a landmarked boundary and the landmark’s reliability for estimating location. Finally, in Part III, I consider the value of sampling during dyadic interactions between individuals. I measured how individual P. bibronii changed their calling behaviour in response to a persistent intruder simulated by a playback device, and reveal that males adjust their behaviour as they gather additional information. Additionally, I analyse a game-theoretic model that considers the functional significance of sampling during contests, which suggests individuals face a trade-off between improving their assessment of opponents and having the capacity to fight for access to fitness-enhancing resources. Furthermore, there can be conflicts over the transfer of information that affect the evolution of sampling. Overall, I conclude that the value of sampling information from the social environment can depend on spatial scale, landmarks and the social interactions within populations. These conclusions may help develop an ecological understanding of how individuals use information.