Emergence, prevalence and consequences of parasites in a songbird

Abstract

Parasites are abundant in nature and known to alter the behaviour of animals. These changes can be directly selected for by the parasite or result from host responses to infection. Nonetheless, these changes can have important consequences for the fitness and survival of animal host species. There is empirical evidence on how parasites can alter host behaviours across diverse animal taxa, ranging from subtle to very striking and apparent changes. However, many of these studies lack the use of robust techniques and methods, and are often conducted within controlled environments potentially minimizing or missing some effects. In this thesis, I worked with a common garden passerine, the great tit Parus major as my model species. I conducted experiments using robust sample sizes and across several behavioural domains in captivity and the wild. This involved the use of laboratory and field techniques, conducting behavioural observations and utilizing a field tracking system. Firstly, I found that pooling samples over a 24hr period per bird greatly improved the detection of parasites within the faeces. In addition, I highlighted the need to choose appropriate laboratory techniques, as the sensitivity may be parasite-specific. Secondly, I discovered and reported new avian host species infected with an air sac nematode Serratospiculoides amaculata. This suggests that this parasite and potentially several others are seeking and colonizing new host species. Thirdly, I observed that personality traits such as boldness may be predicted by Isospora sp. infection load, with bolder birds detected with higher number of Isospora oocysts. Fourthly, I show that parasites can impact social learning, where infected birds were observed to reduce their latency to learn a novel foraging behaviour and were also more frequently engaged in the task. Lastly, I detected changes in social behaviours associated with parasitic infection. Here, I found weak evidence on how infected birds often moved in slightly larger flocks and were more likely to be central within the group i.e. infected birds interacted more frequently with well-connected members of the group. This thesis provides strong evidence on how parasites can alter individual-level behaviours across several domains and how this can translate to changes in social behaviours. These findings are opening up further questions and are pushing the need to explore how parasites can potentially shape important ecological and evolutionary processes.