School of BioSciences - Theses
Permanent URI for this collection
Search Results
1 - 2 of 2
-
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.
-
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.