Ecological immunology and genetic diversity of the endangered Mauritius parakeet

Studies of avian ecological immunology attempt to describe the biotic and abiotic factors which explain natural variation in immune function within and among free-living bird species. Understanding this variation and the trade-offs associated with maintaining appropriate immune defences and individual life history variables has important implications for the conservation of endangered species, many of which are characterised by small population size and reduced genetic diversity. Such species often display increased susceptibility to infectious diseases as a result of inbreeding depression and are prone to the effects of novel parasites and pathogens.

This thesis aims to explain the variation in immune function in the endangered, island-endemic Mauritius parakeet (Psittacula echo), a species which has passed through a considerable population bottleneck but now thrives by virtue of ongoing conservation management despite the presence of a highly infectious disease. Identifying the ecological, environmental and genetic elements which define individual immunity offers the potential to predict the survival probability of juvenile individuals in a disease landscape thereby representing an exciting prospect for the field of conservation reintroduction biology.

Interactions among indices of immune function are investigated at the individual level for Mauritius parakeets and also at the species level with the sympatrically occurring and non-native Indian ringneck parakeet (Psittacula krameri). Patterns of species-level genetic diversity of the Mauritius parakeet spanning two decades are examined and interspecies variation in immune function and genetic diversity is explored. Productivity and survival of Mauritius parakeets is summarised during and after a disease outbreak and an in depth analysis of the predictors of infection status and immunocompetence in this species is offered.

This study highlights the complexity of the immune system and the challenges faced when trying to characterise it among individuals in an ecological context. I reveal a declining trend in species-level genetic diversity among Mauritius parakeets due to low natural dispersal demonstrating the importance of adaptively managing endangered species. I illustrate how, as a result of population bottlenecks or contrasting evolutionary histories that the Mauritius parakeet displays an attenuated immune function when compared to the Indian ringneck parakeet. I find no evidence to suggest that genetic diversity or inbreeding predicts disease infection in Mauritius parakeet nestlings and finally I use long-term monitoring data to cherry pick suitable individuals for reintroduction.